na
za
ud
y.
co
m
CCNA Semester 1 - Technical Diary............................................................................. 2
Part 1 [Chapters 1, 2 and 3] ....................................................................................... 2
1. Technical Content .......................................................................................... 2
2. References ...................................................................................................... 4
3. Straightforward and Difficulties .................................................................... 5
4. Strategies ........................................................................................................ 5
5. Reflections ..................................................................................................... 6
Part 2 [Chapters 4, 5 and 6] ....................................................................................... 7
1. Technical Content .......................................................................................... 7
2. References .................................................................................................... 13
3. Straightforward and Difficulties .................................................................. 14
4. Strategies ...................................................................................................... 14
5. Reflections ................................................................................................... 15
Part 3 [Chapters 7, 8 and 9] ..................................................................................... 16
1. Technical Content ........................................................................................ 16
2. References .................................................................................................... 27
3. Straightforward and Difficulties .................................................................. 28
4. Strategies ...................................................................................................... 29
5. Reflections ................................................................................................... 29
Part 4 [Chapters 10 and 11] ..................................................................................... 30
1. Technical Content ........................................................................................ 30
2. References .................................................................................................... 36
3. Straightforward and Difficulties .................................................................. 36
4. Strategies ...................................................................................................... 37
5. Reflections ................................................................................................... 37
Conclusion ............................................................................................................... 38
Technical Diary – Semester 1
Page 1 of 39
Manuel Munoz Soria – 21076464
CCNA Semester 1 - Technical Diary
m
The purpose of this diary is to reflect my learning experiences during the
lectures of the Cisco course, my own personal research about the technical contents of
the curriculum and how I implement what I have learnt in my daily life and job.
Please note that most of the graphics used in the technical diary have been
extracted form the corresponding chapter on the Cisco Online Resource. In the cases
where the graphics has been copied from an external source, I have acknowledged the
owner with a reference.
Part 1 [Chapters 1, 2 and 3]
na
za
ud
y.
co
1. Technical Content
The first chapter was an introduction to the Cisco course in general, where
we discuss what a converged network1 is and how the computers use a set of rules
called protocols2 to communicate to each other. We learnt that, on a packet switched
network, a message is broken into small blocks called packets 3 that are sent
individually to the network, could take different routes to arrive to their destination
and are reassemble to create the original message at the end device. We also learnt
about the main four block of any network architecture, and these are:
-Fault Tolerance4: There must be some kind of hardware or software
implementation that can allow a quick recovery in case of failures. And whenever
possible, there must other redundant links or paths for the network traffic to flow.
-Scalability5: This is the idea of using layers to design the way a network
works, creating the functionality of changing the contents of each layer without
affecting the design of the others, thus making feasible new upgrades or new
technologies implementations.
- Quality of Service6 (QoS): QoS are a set of mechanism that will prioritise the
packets of certain types of communication in order to avoid congestion of the
network, where the volume of packets could be greater than the devices can handle.
- Security: Privacy is a key component of the exchange of data between
devices, where the aim is to secure the data in a way that nobody but the intended
recipient could read it. Security on the network should ensure confidentiality of the
data as well as its availability, and also maintain communication integrity.
We also study on this chapter the main elements that form a network like
Desktop Computers, Servers, Laptops, Switches, Routers, Firewalls and Media. The
route a message takes when it is sent was explained during this chapter, as it goes
from the sender, through the intermediary devices to reach finally the destination
device.
We were shown the different collaboration tools that users use to
communicate to each other in this World where networks have become very important
and critical for many services. These tools are Internet Relay Chat (IRC), Instant
Messaging (IM), Wikis and Weblogs.
In the second chapter we were more in detail about segmentation7, the
process of dividing data into packets and the benefits it has of making the packets
manageable pieces that are easy to send over the network. The drawback of
segmentation is the complexity that is added in order to achieve the process.
We understood the difference between End Devices (generators or recipient of
data) like workstations, printers and VoIP phones, and Intermediary Devices (direct
the path of the data) like hubs, switches or routers. These Intermediary Devices8 are
able to retransmit data signals, maintain information about available pathways that
Technical Diary – Semester 1
Page 2 of 39
Manuel Munoz Soria – 21076464
za
ud
y.
co
m
could be used to send the data, permit or deny the flow of data based on security
settings and also classification of the data according to QoS priorities.
This chapter two present us with the first contact to the OSI Reference Model9,
and I was surprise to learn that protocols actually do not describe how to accomplish a
particular function, instead they only describe what functions are required for a
particular communication rule; then it is up to the manufacture to achieve that goal,
thus making the protocol technology-independent.
We also review the TCP/IP Protocol Model10 and compare it with the OSI
Model. While the OSI is a reference that helps network design and troubleshooting,
the TCP/IP is a protocol model describing the functions that occur at each layer of the
TCP/IP protocol suite. The definitions of these protocols are discussed in public
forums and defined in public documents called Requests for Comments (RFCs).
The following table compares the two Models; notice that the key parallels
between the two are the Transport layer 4 and the Network Layer 3 for the OSI Model
and the Internet Layer 3 in the TCP/IP model.
na
On the TCP/IP Model, the segmentation process occur at the Application
Layer, where data is broken into smaller pieces called TCP Segments, and each
segment is given a header11 with information about the destination end device.
The encapsulation12 process starts taking place at the Transport Layer, where
the TCP segment is send to the Internet Layer. The Internet Layer attaches an IP
header containing source and destination addresses to the TCP Segment, converting it
into an IP Packet13. The resulting IP Packet is then sent to the Network Access Layer
where it is further encapsulated with a frame header and trailer, containing each frame
the source and destination of the physical address of the devices.
During chapter 3 we dig into the Application Layer and learnt that is directly
responsible for accessing the processes that manage and deliver communication
between humans and computers, allowing us to interact with the network in a way
that is meaningful and effective. Within the application layer there are two forms of
processes that provide access to the network: Application14 and services15.
Applications are programs that interact with the users and initiate data transfers.
Technical Diary – Semester 1
Page 3 of 39
Manuel Munoz Soria – 21076464
za
ud
y.
co
m
Services are background programs that provide the connection between the
application layer and lower layers of the networking model.
We understood the concept of Client-Server Model16, where the client device
request data or a service and the server device respond to the request with a service or
stream of data.
We learnt the terminology of e-mail clients called Mail User Agent (MUA),
and the processes of the e-mail servers that are Mail Transfer Agent (MTA) use to
forward e-mail and Mail Delivery Agent (MDA), responsible for delivering the data.17
We have a look at some of the protocols that operates in the application layer, like
File Transfer Protocol (FTP) used to transfer files, Dynamic Host Control Protocol
(DHCP) used to deliver IP addresses to requesting devices and Server Message Block
(SMB) a client/server file sharing protocol.18
FTP required two connections between the client and server devices, one for
commands and replies (TCP port 21) and another for the actual transfer of files (TCP
port 20).
DHCP pose a security risk because any device connected to a network can
received a valid IP address from the server, opening the door to hackers and packets
sniffers that will use this valid IP address to authenticate to the network. The process
starts at the client where it broadcast a DCHP REQUEST packet to any available
DHCP server. The server in return responds with a DHCP OFFER packets to the
client.19
SMB20 establish a long term connection between the client and the server, thus
allowing the client to access resources on the server as if they were on the client host
itself.
The last important thing that we learn in this chapter was Telnet21, an
application layer protocol that provides a method to connect to other devices on the
network. A connection using Telnet is called a Virtual Terminal (VTY); that creates a
session with access to the command line interface (CLI)22 of the device. Common
Telnet client applications are HyperTerminal, Minicom and TeraTerm, that can be
used to connect and manage Cisco switches.
On the practical sessions we made some RJ45 patch leads cables and the
different ways there are to build cables, depending on what devices they are going to
connect: to connect a switch to a computer it will be a twisted pair cable but to
connect a switch to a switch it will have to be a straight though cable.
2. References
1
na
Leslie T. O’Neil (2007) Best Practices for Managing a Converged Network.
http://www.itmanagement.com/features/10-practices-converged-network-082807/
[Accessed: 9 November 2009]
2
Peter Loshin (2003) TCP/IP Clearly Explained. [Online] Available at:
http://books.google.co.uk/books?id=7ppuc1BrLCQC&lpg=PA25&ots=_zTF30VxQQ&dq=protocols%20rules%20
explained&pg=PA25#v=onepage&q=&f=false [Accessed: 9 November 2009]
3
What is a Packet? How stuff works. http://computer.howstuffworks.com/question525.htm [Accessed 9 November
2009]
4
Bran Selic (2004) Fault tolerance techniques for distributed systems
http://www.ibm.com/developerworks/rational/library/114.html[Accessed 9 November 2009]
5
Scalability Overview http://msdn.microsoft.com/en-us/library/aa292203(VS.71).aspx [Accessed 10 November
2009]
6
QoS Concepts http://www.cisco.com/en/US/docs/internetworking/technology/handbook/QoS.html#wp1020563
[Accessed 10 November 2009]
7
Segmentation and Reassembly. http://en.wikipedia.org/wiki/Segmentation_and_Reassembly [Accessed 10
November 2009]
Technical Diary – Semester 1
Page 4 of 39
Manuel Munoz Soria – 21076464
8
co
m
Intermediary Devices and their Role on the Network. http://www.orbit-computer-solutions.com/IntermediaryDevices-and-their-Role-on-the-Network.php [Accessed 10 November 2009]
9
OSI Reference Model Illustrated. http://whatis.techtarget.com/definition/0,,sid9_gci523729,00.html [Accessed 10
November 2009]
10
TCP/IP Model. http://en.wikipedia.org/wiki/TCP/IP_model [Accessed 10 November 2009]
11
IP Header. http://www.tekelec.com/ss7/protocols/ip2.asp [Accessed 10 November 2009]
12
Understanding Data Encapsulation. http://www.tech-faq.com/understanding-data-encapsulation.shtml [Accessed
10 November 2009]
13
IP Packet Structure. http://www.freesoft.org/CIE/Course/Section3/7.htm [Accessed 10 November 2009]
14
Application Software. http://en.wikipedia.org/wiki/Application_software [Accessed 10 November 2009]
15
Network Services. http://en.wikipedia.org/wiki/Network_service [Accessed 20 November 2009]
16
What is Client Server Network Technology? http://compnetworking.about.com/od/basicnetworkingfaqs/a/clientserver.htm [Accessed 10 November 2009]
17
How email works (MTA, MDA, MUA). http://en.kioskea.net/contents/courrier-electronique/fonctionnementmta-mua.php3 [Accessed 10 November 2009]
18
TCP/IP Protocols Reference Page. http://www.protocols.com/pbook/tcpip1.htm [Accessed 11 November 2009]
19
DHCP Process. http://www.inetdaemon.com/tutorials/networking/lan/dhcp/process.shtml[Accessed 11
November 2009]
20
Sever Message Block http://en.wikipedia.org/wiki/Server_Message_Block [Accessed 11 November 2009]
21
The TCP/IP Guide. Telnet Overview.
http://www.tcpipguide.com/free/t_TelnetOverviewHistoryandStandards.htm [Accessed 11 November 2009]
22
Telnet Tools and Settings. http://technet.microsoft.com/en-us/library/cc787407(WS.10).aspx[Accessed 11
November 2009]
na
za
ud
y.
3. Straightforward and Difficulties
The material of Chapter 1 was easy to understand; it mainly covered common
sense approach about the way computers communicate to each others by the use of
protocols. The comparison of two computers communicating and two people talking
to each other help me a lot to visualise in my mind how protocols work on the
computer world, and the set of rules (that we humans call languages) there have to be
in place before any attempt of communication is made between devices. The chapters
that follow were a bit denser but still I manage to understand them. However, I found
a bit hard to memorise and get accustom to the new terminology like Fault Tolerance,
Quality of Service and Converged Network, and had to do some further reading
elsewhere to fully understand these terms.
What I also found difficult is the interface for the CCNA Exploration Network
Fundamentals course online; is confusing and certainly not user friendly. It takes a
while to logon to the NetAcad website, go through the puzzling menus and finally be
able to launch the interactive course. And when it finally launches, the graphs and
pictures that are displayed on the right hand side are not always self explanatory and
sometimes either very simplistic or quite obscure. In addition, the main disadvantage I
found when using the Cisco online course on NetAcad is the timeout session: after a
few minutes on the same slide of the CCNA Exploration you session timeout, and you
are asked to log back in again starting from the beginning, losing track of what you
were doing and wasting precious concentrated time on logging back in again and wait
for the application to launch. I was therefore force to read quickly and finished the
chapter as soon as possible in case my session will expire.
4. Strategies
The timeout of the NetAcad website made me uncomfortable when reading
slides, as I am not entirely sure how long will I have before the session expires.
Another associated problem to this is that I can not really do any serious research
about a particular slide, analyzing its contents on the Internet, because after a few
minutes looking for extra information about the concepts explained on the slide, I
found that my session has expired when I try to continue, making difficult (when you
Technical Diary – Semester 1
Page 5 of 39
Manuel Munoz Soria – 21076464
co
m
log back in again) to find the exact position you were working on (no features for
making bookmarks!).
I sent an e-mail to the Academy Cisco Support, asking them to disable this
setting, to let us know how long the session last or to allow us to customise the
duration of our session. They replied to me saying that this behaviour of the course is
part of their Cookie Policy, and they could not do anything about it to prevent it. I had
the impression that the real functionality of their Cookie Policy was to track how
many hints and forced visited they received on their website in detriment of student
concentration and performance.
After searching for the contents of the course using P2P sharing programs, I
found the whole material and I download it to my computers. I do not believe this is
illegal, because I am a legitimate student of this course and Cisco should have
provided the course off-line anyway (what happens if I do not have an Internet
Connection?).
na
za
ud
y.
5. Reflections
I have the advantage of having a Microsoft Certification obtained last year,
and some of the terminology shown in the course sound familiar to me, making easy
for me to comprehend the whole picture of what we are learning and digest the
terminology of the Cisco material course. However, I obtained my Microsoft
qualification over a extended period of four years, and most of the basics concepts
that I learnt at the beginning are now too far in the distant memory to bring them back
clearly. I hope that, as I go along in the Cisco course, some of the things that I studied
while preparing for the Microsoft exams, will come to the surface of my memory and
help me to facilitate the understanding of the concepts in this Cisco course.
So far the course seems to be pretty intense, full of exercises using Packet
Tracer that we have to do at home. We also have the target of doing a chapter a week,
in other words, one exam per week. This course is going to last two years, and I had
the impression at first (I was wrong) that the material of the Cisco course would be
easy because it will need to be stretch alongside a two years study curriculum, but I
just realised how much there is to learn about Cisco networking. These two years will
be intensive.
Technical Diary – Semester 1
Page 6 of 39
Manuel Munoz Soria – 21076464
Part 2 [Chapters 4, 5 and 6]
na
za
ud
y.
co
m
1. Technical Content
The focus of chapter four was the Transport Layer1, which is responsible for the
overall end-to-end transfer of application data, accepting data from the Application
Layer and preparing it for addressing at the Network Layer. Some of the functions of
the Transport Layer include error handling mechanism to ensure the data is received
correctly, as well as adding a header to indicate what sort of communication is
associated with the data, creating an encapsulated segment2.
The two common protocols of the Transport Layer are TCP and UDP. Chapter for
is dedicated to the study of these protocols, the applications that they support and the
different ways that they both manage communication.
User Datagram Protocol (UDP3) is a connectionless protocol, meaning that it
does not establish a connection before sending the data. UDP is described in RFC
7684 and, because it does not check if the data has arrived correctly to the destination,
it provides a low overhead data delivery. UDP simply reassembles the data in the
order that it was received and then sends it to the application. Some of the
Applications that use UDP are Domain Name System (DNS), Dynamic Host
Configuration Protocol (DHCP), Simple Network Management Protocol (SNMP),
Voice Over IP (VoIP) and Trivial File Transfer Protocol (TFTP)5.
Transport Control Protocol (TCP6) is, on the other hand, a connection-oriented
protocol described in RFC 7937. This protocol provides flow control, order and
reliable delivery, but it incurs in additional overhead to gain all these functions.
Unlike UDP, each of the TCP segment headers contains a sequence number that
allows the Transport Layer to reassemble the segment in the order they were
originally transmitted, thus ensuring the destination device has all the data that was
intended.
TCP has a system called three-way handshake to establish a connection to the
host. This process is composed of six 1-bit values, referred as flags8, within the TCP
segment header, that control the information contained in the segment. These flag
fields are:
URG – Urgent pointer field significant
ACK – Acknowledgement field significant
PSH – Push function
RST – Reset the connection
SYN – Synchronize sequence numbers
FIN – No more data from sender
Depending on the position of the bit on the above fields (it can only be 1 or 0) the
value associated to its position is assigned to the segment.
Another important thing to consider is the window size9 of the TCP header, which
determines the amount of data the source device can transmit before waiting for an
acknowledgment. The window size is a field part of the TCP header, and is crucial for
the management of data lost and flow control. It can determine the number of bytes
sent before an acknowledgment is expected. Sometimes the TCP window size is
dynamic, and it increase or decrease to optimize the transmission. On efficient
network the window size may be large while on networks with lots of traffic it will
remain small.
Technical Diary – Semester 1
Page 7 of 39
Manuel Munoz Soria – 21076464
The UDP PDU (Protocol Data Unit) is referred sometimes as a datagram10, and it
has 8 bytes of overhead in the encapsulating header; while the IP PDU is known as a
segment and it has 20 of overhead. The following table illustrate the different name
PDU obtains as it climbs the layers of the OSI Layer Model11.
Naming Conventions according to OSI Layer
Protocol Data Unit (PDU)
OSI Layer
Session
Transport
Network
Data Link
Physical
m
Data
Segment / Datagram
Packet
Frame
Bits
na
za
ud
y.
co
During this chapter we leant that, while server processes have static port numbers
assigned to them, clients dynamically use a port number for each of the conversation
that they have. We also review some important terminology like socket12, which is a
combination of the Transport layer port and the Network layer IP addresses assigned
to a unique host, so that a particular process running on this host can be identify. As
an example I could say that if a computer is requesting a web page hosted on a web
server with IP 192.168.0.1 and the dynamic port assigned to the web browser is
49152, the socket for the page would be 192.168.0.1:49152.
We also went into more details in the way computers communicate to each other
by the mean of transmission ports. The Internet Assigned Numbers Authority13
(IANA) is the body responsible for assigning various addressing standards for the
web. They have assign different port number to the communication transmission of
computers, these are:
Well Know Ports14 (from 0 to 1023): They are reserved for services and
applications like HTTP, POP3, SMTP, Telnet, etc
Registered Ports (from 1024 to 49151): They are assigned to specific and
individual applications that a user has decided to install. When these ports are not in
use for a server resource, they may be used dynamically by the client as its source
port.
Dynamic or Private Ports15 (from 49152 to 65535): They are assigned
dynamically to client applications when initiating a connection, and are also known as
Ephemeral Ports.
When a client initiates a transmission with a server, it randomly selects a port
from the dynamic range and uses it as the source port for the conversation. The
destination port is normally a Well-Known or a registered port assigned to a particular
process or service on the server. Once the source and destination ports are clear, the
same pair of ports is used in the header of all datagram used for the transmission.
When data returns to the client from the server, the source and destination port
numbers are reversed.
On Chapter five we run through a deep understanding of the Network Layer
(OSI Layer 3), and learnt that this layer is use to connect processes and devices,
providing encapsulation of data and allowing the contents to be passed within network
with minimal overhead. To accomplish this end-to-end transport, the Network Layer
uses four basic processes16:
1.-Addressing: each device on the network must have a unique IP address, which
is a 32-bit IPv4 address. That makes the identification of the device unique on the
network making the routing communication process possible.
Technical Diary – Semester 1
Page 8 of 39
Manuel Munoz Soria – 21076464
na
za
ud
y.
co
m
2.-Encapsulation: During the encapsulation process the Network Layer 3 adds a
head to the packet it receives from the Transport Layer 4. This header contains the
source and destination addresses that will help route its delivery.
3.-Routing: The process of the IP packet travelling from source to destination is
called routing, and it is done my intermediary devices called ‘routers. Each path that
the packet takes for its destination is called hope, and there are a limited number of
hopes that an IP packet can travel before being discard.
4.-Decapsulation: If the address destination for the packet is correct, the deencapsulation process starts and the Network Layer 3 passes the packet to appropriate
service at the Transport Layer 4.
The most significant protocol of the Network Layer 3 is the IP Protocol. IPv4 is
widely use it, though is slowly been replaced by IPv617. Other protocols of this layer
are Novell Internetwork Packet Exchange (IPX), Apple Talk, etc.
The Internet Protocol provides only the functions necessary to deliver a packet
from source to destination over the network. This protocol is not designed to manage
or track the flow of data, and these functions are performed by other protocols in other
layers. The basic characteristics of the IP protocol are:
1.-Connectionless Service: Unlike TCP, which is a connection-oriented protocol,
IP does not required initial exchange of information to establish a connection before
packets are send, it just send them which greatly reduces the overhead of IP. Packets
may arrive out of sequence to the destination, but it is the job of the upper layers so
solve this problem.
2.-Best Effort Service: IP is referred to as an unreliable protocol, meaning that it
has no capabilities to manage or recover packets that are undelivered or corrupted. As
mentioned before, protocols at other layers will manage the reliability of the transport.
3.-Media Independent: IP operates independently of the media that carries the
data; however there is a maximum size of the PDU that each medium can transport.
This maximum size is called Maximum Transmission Unit18 (MTU), and it is the
mission of the Data Link Layer to passes the correct MTU for the media used to the
Network Layer. The process called fragmentation occurs when a router split up an IP
packet to send from one media with a type to MTU to another media with a smaller
size of MTU.
The IP Header19 of an IP packet contains binary values or fields that help forward
the packet across the network. The most relevant fields are:
1.-IP Destination Address: 32-bit binary value that represent the host address.
2.-Time-to-Live: 8-bit binary value indicates the ‘life’ of the packet. Each time it
passes through a route, the TTL is reduced by one. When the value reaches zero, the
packet is discharged or dropped.
3.-Protocol: 8-bit binary value that represents the type of data a packet is carrying
(01 for ICMP, 06 for TCP, 17 for UDP, etc).
4.-Type-of-Service: 8-bit binary value that determines the priority of each packet.
The Quality-of-Service uses this field to prioritize packets carrying voice data.
5.-Fragment Offset: 13-bit binary value that, together with the MF flag, allow the
receiver device to reconstruct the IP Packet if fragmentation has occurred during the
transmission.
6.-Flag: 3-bit binary value that indicates flags like MF (More Fragment) or DF
(Don’t Fragment), to determines if the packet has been fragmented during
transmission.
7.-Version: Display the IP version number (4 or 6).
8.-Header Length (IHL): Specifies the size of the packet header.
Technical Diary – Semester 1
Page 9 of 39
Manuel Munoz Soria – 21076464
m
9.-Identification: Identify fragments of an original IP packet.
10.-Header Checksum: Use for error checking the packet header.
11.-Options: Provide fields for other services that are rarely used.
co
20
na
za
ud
y.
Large networks are separated into smaller network21 (called subnetworks or subnets)
to make the number of hosts more manageable. Network designers could decide to
group the hosts geographically, by purpose or by ownership. This division of
networks provides the following enhancements:
1.-Improved Performance: by dividing the network into subnets, we can limit
the boundaries of broadcast messages and control the bandwidth that resources utilize.
2.-Increased Security: division of subnets allow the implementation of
intermediate security devices (like routers and firewall) at the perimeter of the
network, prohibiting, monitoring or allowing only trusted data to access the network.
3.-Address Management: to forward packets, hosts only need to know the
address of an intermediary device (caller router or gateway) to which send packets for
all other destination addresses.
IPv4 addresses22 are divided in four groups of eight bits called octets, and its
logical representation is made of two parts, one to identify the network and the second
to identify the host on that network. Routers only need to know the location of the
network to address the packet.
A default gateway23 should be configured on every host to enable
communication with other networks. This default gateway or router uses a series or
protocol to deliver the packet to the correct network. When the packet arrives to the
router, the first thing the router does is to compare its destination address with the
routing table that each router has. If it finds a matching route, it sends the packet to
the next hope. If it finds that the destination address is within its own network, it
delivers the packet to the addresses host. If there is no matching address, the TTL is
no expires and there is no matching host, then the packet is dropped. If the router
finds two or more possible routes, it determines the best one by using looking at the
metric value of every route.
Routing tables24 can be manually entered by an administrator on the device
(static routing) or calculating dynamically by the means of Routing Protocols25. The
protocols are use by router to determine the best path for delivery of the packet to
destination, and the most common are:
1.-Routing Information Protocol (RIP)
2.-Open Shortest Path First (OSPF)
3.-Enanced Interior Gateway Protocol (EIGRP)
The most discussed Chapter 6 is based on Addressing the Network, this is to
say, in dividing network in subnetworks to utilise the IP address and optimize network
Technical Diary – Semester 1
Page 10 of 39
Manuel Munoz Soria – 21076464
za
ud
y.
co
m
traffic. This subnet calculation also determines what portion of an IP Address belongs
to the subnetted network and which one to the host. We were introduced to the
Network Prefix terminology or CRID26 (Classless Interdomain Routing Notation),
when a subnet mask is represented by the number of bits that are on, for example
255.255.255.0 could be represented as /24.
One of the first things that we learnt was the three different ways that hosts
communicate to each other on a network27:
1.-Unicast: send a packet from one host to an individual host.
2.-Broadcast: send a packet to all the hosts on the network. Routers do not forward
broadcast, and they form the boundary for what is called a broadcast domain. Many
network protocols such as Dynamic Host Control Configuration (DHCP) and Address
Resolution Protocol (ARP) use broadcasts to function.
3.-Multicast: send the packet to a selected group of host on the network
We have a look at the different types of IP addresses, like the one assigned to the
host, the broadcast address (were all bits of the host portion are turn on or set to 1),
the loopback address28, which is 127.0.0.1 and is used to test the TCP/IP Protocol
stack on the computer.
The link-local addresses or AISP (Automatically Assigned IP Addresses)29 are on
the range 168.254.0.0 to 169.254.255.255, and they are assigned by the Operating
System to the host when there is no IP configuration available, e.g. when a DHCP
cannot be contacted.
There are three ranges of called Private Addresses30 that routers will not forward
to other network and are therefore design to be used locally:
Class A: From 10.0.0.0 to 10.255.255.255
Class B: From 172.16.0.0 to 172.31.255.255
Class C: From 192.168.0.0 to 192.168.255.255
The rest are experimental addresses, and within this range we have the Multicast
Addresses from 224.0.0 to 239.255.255.255, used for multicast groups on a local
network. Packets to these destinations are always transmitted with a TTL value of 1;
this is why routes connected to the local network will never forward them. A special
address could be the 224.0.1.1, reserved for Network Time Protocol (NTP) to
synchronise the time-of-day clocks of the network devices.
One bit can only be either turn on or off, thus representing the value of 1 or 0.
Focusing on subnetting now, we learnt how to covert to binary the decimal
representation of an IP address, and that one byte contains 8 bits, and each one of then
is been assigned a numeric value and also an added value which is the sum of the bits
that are turn on (set to 1). This table illustrate the bit positions and values of one byte:
na
Bit Order
Numeric Value
Added Value
8
128
128
7
64
192
6
32
224
5
16
240
4
8
248
3
4
252
2
2
254
1
1
255
There are also a number of rules31 at the time of addressing a host, and these rules are
dependable of the Class of IP Address32 that we want to use, Class A, B or C. For
example, one of the rules said that for a Class A IP address the first bit must be turn
off, and this is why a Class A IP address can’t have a higher value than 127. The
following table represents the IPv4 rules:
Technical Diary – Semester 1
Page 11 of 39
Manuel Munoz Soria – 21076464
B
Rules
- A rule state that none of the bits can’t either
be all turn off (= to 0) or all turn on (= to 1)
- 1st bit must be off (higher order bit)
- 127 network is used for loopback only
- 1st bit must be on and second bit off
C
- 1st two bit must be on and third must be off
A
Maximum Value on octects
000 0000 = 0 (network address)
1111 1111 = 255 (broadcast address)
0000 0001 = 1 is the lowest value
0111 1111 = 127 is the highest value
1000 0000 = 128 is the lowest value
1011 1111 = 191 is the highest value
1100 0000 = 192 is the lowest value
1101 1111 = 223 is the highest value
Valid Range
1 to 126.0.0.0
128 to 191.0.0.0
192 to 223.0.0.0
m
Class
---
Binary33 is a numeric system based in the radix of 2, and to start calculating
subnets34 we need to be aware of the table of power of 2, which I have represented on
the right hand side up to the value of 12.
For the maximum number of subnets:
(2 (number of bits that are turn on)) – 2
No of bits
1
2
4
8
16
32
64
128
256
512
1024
2048
4096
8192
16382
32768
co
To calculate the number of subnets and host per
subnets we use the following formulas:
Power of 2
20
21
22
23
24
25
26
27
28
29
210
211
212
212
213
214
ud
y.
For the maximum number of hosts per subnet:
(2 (number of remaining bits, the ones that are off)) – 2
na
za
The above formulas are known as part of the ‘subnet zero concept35’, and are
almost obsolete.36 The Cisco formulas are the same but without dividing by 2.
The multiplier is the number of bits that are off on the octet that we are
subnetting, and knowing the value of the multiplier will help you to determine at what
rate the subnets are increasing.
The allocation of IP addresses on the network should be designed carefully
and be well planned and documented in order to prevent duplication and provide the
best possible implementation. One useful tool in the addressing plan in the creation of
a network diagram37, as well as a list of the division and assignments of available
subnets, making sure that the sizes will cope with the demands.
During this long chapter 6, we went into details of Internet Assigned Numbers
Authority (IANA), the organisation that manages the IP addresses of the whole
Internet, and that in the mid-1990s delegated part of the remaining IPv4 addresses to
companies called Regional Internet Registries38 (RIRs), who manage the IP addresses
for specific areas of the globe.
However, most organisations obtain their IP addresses from ISP companies
(Internet Service Providers), together with other services like web hosting, DNS39, email, etc. ISPs are structured hierarchically40, depending of close their connection is
to the backbone of the Internet, they can be divided in Tier1 (large international
companies directly connected to the Internet backbone) Tier 2 (obtain their
connection from Tier 1 and provide Internet generally to business customers) and
Technical Diary – Semester 1
Page 12 of 39
Manuel Munoz Soria – 21076464
m
finally Tier 3, who purchase the service from Tier 2 ISP and deliver the connectivity
to home users or customer with little or no computer expertise.
IPv641 was created in the early 1990s by the Internet Engineering Task Force
(IETF) and was meant to provide more scalability and expansion of the addressing
capabilities, eventually replacing IPv442. Some of the relevant features of IPv6 are:
128-bit hierarchical addressing, unlike Ipv4 which is 32-bit
Integrated security like authentication and privacy
Flow labelling capability as QoS mechanisms
Header format simplification to improve packet handling
2. References
1
na
za
ud
y.
co
Transport Layer: Information from Answers.com http://www.answers.com/topic/transport-layer [Accessed 27
December 2009]
2
Understanding Data Encapsulation. http://www.topbits.com/understanding-data-encapsulation.html [Accessed 27
December 2009]
3
User Datagram Protocol – Wikipedia http://en.wikipedia.org/wiki/User_Datagram_Protocol [Accessed 27
December 2009]
4
RFC 768 User Datagram Protocol. http://www.faqs.org/rfcs/rfc768.html [Accessed 27 December 2009]
5
The TCP/IP Guide – UDP Common Applications and Server Port Assignments
http://www.tcpipguide.com/free/t_UDPCommonApplicationsandServerPortAssignments-3.htm [Accessed 27
December 2009]
6
Transmission Control Protocol http://en.wikipedia.org/wiki/Transmission_Control_Protocol [Accessed 27
December 2009]
7
RFC 793 Transmission Control Protocol http://www.faqs.org/rfcs/rfc793.html [Accessed 27 December 2009]
8
TCP Analysis Flag Options. http://www.firewall.cx/tcp-analysis-section-4.php [Accessed 27 December 2009]
9
TCP Window Size Adjustment and Flow Control
http://www.tcpipguide.com/free/t_TCPWindowSizeAdjustmentandFlowControl.htm [Accessed 27 December
2009]
10
Frames, Packets and PDU’s
http://www.inetdaemon.com/tutorials/basic_concepts/communication/frames_packets_n_pdus.shtml [Accessed 27
December 2009]
11
OSI Protocol Stack Description http://www.interfacebus.com/Design_OSI_Stack.html [Accessed 27 December
2009]
12
Internet Socket http://en.wikipedia.org/wiki/Internet_socket [Accessed 29 December 2009]
13
IANA – Internet Assigned Numbers Authority http://www.iana.org/ [Accessed 29 December 2009]
14
Well Known IP Ports http://www.networksorcery.com/enp/protocol/ip/ports00000.htm [Accessed 29 December
2009]
15
List of TCP and UDP port numbers http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
[Accessed 29 December 2009]
16
The TCP/IP Guide Network Layer (Layer 3) http://www.tcpipguide.com/free/t_NetworkLayerLayer3.htm
[Accessed 29 December 2009]
17
Differences IPv4 Vs IPv6 http://www.techsutram.com/2009/03/differences-ipv4-vs-ipv6.html [Accessed 29
December 2009]
18
What is maximum transmission unit?
http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci213605,00.html# [Accessed 29 December 2010]
19
IP Header http://www.tekelec.com/ss7/protocols/ip2.asp [Accessed 29 December 2009]
20
IP Header Diagram. [http://labspace.open.ac.uk/file.php/4918/ipheader.gif]
21
What is a subnetwork or subnetting?
https://support.comodo.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=432 [Accessed 29
December 2009]
22
How Stuff Works – What is an IP Address? http://www.howstuffworks.com/question549.htm [Accessed 29
December 2009]
23
What is the default gateway http://kb.iu.edu/data/ajfx.html [Accessed 29 December 2009]
24
Routing tables http://compnetworking.about.com/od/hardwarenetworkgear/f/routing_table.htm [Accessed 29
December 2009]
25
Routing Protocols http://www.skullbox.net/routing.php [Accessed 29 December 2009]
26
CIDR Notation http://compnetworking.about.com/od/workingwithipaddresses/a/cidr_notation.htm [Accessed 30
December 2009]
27
What is unicast, broadcast and multicast? http://www.networkguruz.com/networking-basics/what-is-unicastbroadcast-and-multicast/ [Accessed 30 December 2009]
28
Loopback http://en.wikipedia.org/wiki/Loopback [Accessed 30 December 2009]
Technical Diary – Semester 1
Page 13 of 39
Manuel Munoz Soria – 21076464
29
co
m
How is my IP address assigned? Leo Notenboom http://ask-leo.com/how_is_my_ip_address_assigned.html
[Accessed 30 December 2009]
30
Private Network http://en.wikipedia.org/wiki/Private_network [Accessed 30 December 2009]
31
IP Addresses Rules http://www.noc.ucf.edu/IPAddressRules.htm [Accessed 30 December 2009]
32
IP Addressing, subnet mask, wildcard mask http://www.rhyshaden.com/ipadd.htm [Accessed 30 December
2009]
33
Binary Numbers http://php.about.com/od/programingglossary/qt/binary.htm [Accessed 30 December 2009]
34
Get a Clue: Calculating Subnet Masks http://www.networkclue.com/routing/tcpip/calculating-masks.aspx
[Accessed 30 December 2009]
35
Subnet Zero and the All-Ones Subnet
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml [Accessed 30
December 2009]
36
Subnet Zero Concept http://www.subnettingquestions.com/subnetzero/ [Accessed 30 December 2009]
37
Network Diagram http://en.wikipedia.org/wiki/Network_diagram [Accessed 30 December 2009]
38
History of RIRs http://www.nro.net/archive/news/rir-history.swf [Accessed 30 December 2009]
39
The TCP/IP Guide – DNS Hierarchical Authority
http://www.tcpipguide.com/free/t_DNSHierarchicalAuthorityStructureandtheDistributed.htm [Accessed 30
December 2009]
40
HowStuffWorks – The Internet Network Hierarchy http://www.howstuffworks.com/internet-infrastructure1.htm
[Accessed 30 December 2009]
41
IPv6 http://en.wikipedia.org/wiki/IPv6 [Accessed 30 December 2009]
42
IPv4 vs IPv6 – Guides & Tutorials http://forums.techarena.in/guides-tutorials/1064417.htm [Accessed 30
December 2009]
za
ud
y.
3. Straightforward and Difficulties
I strongly believe that there has not been a part of this section of the diary that
I would consider easy or straightforward, maybe I would say there were difficult parts
and less difficult parts. Among these less difficult parts were the materials of the first
two chapters, where we study the Transport and Network layer. The instructor
presented the subjects of each chapter really well and the routine and organisation of
the classes took place when we most needed, which is great. The presentations that
the teacher was showing and explained to us really help me digest the terminology
and the concepts of this part of the diary.
Without any doubt, chapter 6 was a challenge to all of us. It is so far the
hardest material of all that we have to assimilate, full of complexity, with numbers,
calculations and mathematical thoughts that for a moment made me believe I was
doing a course related to stock exchange rates, where we have to calculate the exact
number for every specific environment that is in need of IP subnetting. Luckily for us,
the concepts of chapter 6 were covered during a period of two weeks, which gave us
the crucial extra time to truly understand this important aspect of network and IP
addressing.
na
4. Strategies
Using the off line Cisco content that I had on my computer, I started to copy
and paste some of the text I needed for extra reading into a document, creating a draft
text of the online course. I structured this document on chapters as it was on the
online material and then printed each chapter so that I could read it on my spare time.
I learn better when I have papers at hand; the online course is not good enough on its
own to pass this Cisco course and that is why I created this extra printed help. A few
days after starting that, I saw online the book for this course, and I thought about
buying it, but changed my mind and continue with the process of resuming the online
content into a draft document. Then, from this draft document, I extracted the ideas
and materials to start doing this Technical Diary.
The Foundation Degree sometimes requires us to be at TVU on Saturdays for
specific lectures timetabled on weekends, but I have realised that the Saturday we do
Technical Diary – Semester 1
Page 14 of 39
Manuel Munoz Soria – 21076464
not need to go to TVU does not mean that we have the day free. I am working now
every single Saturday, either at TVU if there is a lesson, or at home catching with the
TVU Problem Solving Module or preparing myself for the next Cisco lesson taken
place on Wednesday. All Saturday mornings are dedicated to my studies. This is a
must if I really want to obtain the CCNA certification and a degree.
na
za
ud
y.
co
m
5. Reflections
It is indeed very frustrating to discover the poor layout of Cisco at the time of
designing the content of this particular Network Fundamental course. The first five
chapters were perfect, in the sense that they build into one another, going through the
OSI Model layer as we study one specific layer per week. However, I believe the
Network Layer should have been divided into two chapters, one for the functions of
the layer itself and another one to study the IP Header only. And so the same for
Chapter 6, it should have been divided in two separate chapters, one to understand the
different types of IP addresses and the other to deal with subnetting only.
The workload of the course that we have to do has increased dramatically
during Chapter 6, and I have to thank all the support given by the teacher and the
practical that we do with the Cisco Technician every Wednesday. Their tips and
approaches really help me to get the grips of subnetting, performing network
calculations in a matter of minutes, though the learning road to get that knowledge has
not been easy.
Technical Diary – Semester 1
Page 15 of 39
Manuel Munoz Soria – 21076464
Part 3 [Chapters 7, 8 and 9]
za
ud
y.
co
m
1. Technical Content
For Chapter 7 we scrutinise the Data Link Layer, layer number 21 in the OSI
model. So far we have seen that the Application layer 1 provides the interface for the
user, the Transport layer 4 is responsible for managing communications between
processes, while Network layer 3 organise the data so that it can travel across
networks. It is the role of the Data Link layer 2 to prepare the Network layer 3 packets
for transmission, provide error detection and control access to the physical media.
Data Link layer 2 processes2 occur both in hardware and software, and to support
this variety of network functions, the Data Link is divided in two sublayers3, one
focusing in software and the other one in hardware. These two sublayers are:
-Logical Link Control4 (LLC) identifies which Network layer 3 protocol, such as
IP or IPX, is being used for the frame.
-Media Access Control5 (MAC) provides addressing and delimits the data
according to the physical signalling requirement of the medium and the type of
protocol in use. This addressing technique is implemented by the means of a MAC
address, a 48-bit hexadecimal number assigned to every Physical Layer 1 device.
na
Data Link layer 2 uses two basic methods for controlling the access 6 to the media,
these are:
-Controlled, also known as schedule or deterministic, where each device has its own
time to use the medium. This provides well-ordered access to the media, but is
inefficient because a device has to wait for its turn before it can be use the medium.
-Contention-based, where all devices compete for the use of the media. To detect if
another device is transmitting and prevent chaos, this method uses a Carrier Sense
Multiple Access7 (CSMA) process that helps avoid collisions. This signal carrier
method is usually implemented with either of these two methods for detecting
collisions:
-CSMA/CD (Collision Detection); the device monitors the media and transmit when
there is not data signal presence, indicating that the media is free. If another device
transmits at the same time, all devices will stop their transmission and will try them
later. Traditional Ethernet uses this method.
Technical Diary – Semester 1
Page 16 of 39
Manuel Munoz Soria – 21076464
-CSMA/CA (Collision Avoidance); the device examines the media for the presence of
a signal first, and if the media is free it sends a notification to transmit. This method is
used by wireless networking 802.11.
co
m
The topology of a network8 is the arrangements of devices and the connections
between them. We have to distinguish between physical topology, the actual physical
connections between devices, and logical topology, the way the networks transfer the
information between nodes. The logical topology9 is independent of the physical
network layout, and the most commonly used topologies are:
1. Point-to-point topology, where the media interconnects just two nodes and they do
not have to share the media. The data can flow in one direction only, half-duplex, or
in full-duplex mode if the transfer occurs simultaneously on each direction.
2. Multi-access topology occurs when the media is shared. Every device sees all the
information travelling on the media, but the contents of the frames are processes only
by the nodes to which it is addressed.
3. Ring topology is when each node receives a frame in turn; if the frame is not
addressed to the node, it passes it to the next node. The method of transmission is
called Token passing and allows the ring topology to control the media.
ud
y.
During this chapter we also study the three basic parts that form the frame of a
given protocol running on the Data Link Layer. The three main parts of a frame are:
10
na
za
1. Header. It contains the source and destination address fields, as well as other fields
that include the priority, quality of service and the type of upper layer service
containing in the frame.
2. Data contains the user data to be transmitted.
3. Trailer. It contains a field called Frame Check Sequence11 (FCS) that determines if
the frame has arrived without errors. Note that FCS only provides error detection, and
no correction. The way the Frame Check Sequence detects and error is by looking at
the value of the Cyclic Redundant Check12 (CRC), created by the transmitting node to
summaries the contents of the frame.
The last thing that we look up during this chapter was the different protocols running
on the OSI Data Link Layer 2 that are covered in the CCNA course. Some of these
protocols13 are Ethernet, Point-to-Point Protocol (PPTP), Frame Relay, Asynchronous
Transfer Mode (ATM), etc.
Ethernet is the most widely use LAN technology, and if fact the Ethernet protocol is a
family of networking technologies defined in the IEEE 802.2 and 802.3 standards14. It
provides unacknowledged connectionless service over a shared media using
CSMA/CD as the media access control.
Other common protocol is the Point-to-Point, mainly used for connecting WANs,
defined by RFCs (Request for Comments).
Technical Diary – Semester 1
Page 17 of 39
Manuel Munoz Soria – 21076464
na
za
ud
y.
co
m
The Wireless Protocol, defined in 802.11, has additional controls to challenge the
environment of wireless where the transmission takes place.
The following pictures are frame structures samples of both the Ethernet Protocol and
Point-to-Point Protocol, so we can see the differences in the structure. Both frames
follow the standard of Header-Data-Trailer, but with variations.
Technical Diary – Semester 1
Page 18 of 39
Manuel Munoz Soria – 21076464
ud
y.
co
m
Chapter 8 landed on the OSI Physical Layer 1, the bottom layer, whose
function if to control how the data in placed on the media and then transmitted as
signals. It also has the responsibility of retrieving these signals from the media and
passes them to the Data Link Layer 2 as a complete frame. This diagram represents
clearly the flow of packets through the OSI Layer Model:
na
za
What the media carries is only signals, and there are three basics forms of network
media where the bits are represented:
-Copper Cable; signal the bits as patterns of electrical pulses.
-Fiber; signal the bits as patterns of lights.
-Wireless; signal the bits as patterns of radio transmission.
The Physical Layer Standards are implemented in hardware, developed by
engineers in the form of circuits, media and connectors. While the standards of upper
layers are implemented in software and defined by the Internet Engineering Task
Force15 (IETF) in RFCs, the technologies use in the Physical Layer are defined by
organisations such as the International Organisation for Standardisation (ISO) or the
Institute of Electrical and Electronics Engineers (IEEE).
The three fundamental functions of the Physical Layer16 are the physical
components, the data encoding and the signalling. In this chapter we study each
section in detail.
1. Physical Components. First of all we have to understand that different media
transfer the bits at different speeds, and that this transfer of data can be measured in
three ways:
-Bandwidth17; the amount of information that flows from one place to another in a
given amount of time. Bandwidth is normally measured in megabits per second
(Mbps)
-Throughput18; this is the transfer of bits across the media over a given period of time,
and usually id does not match the bandwidth specified by the media. Throughput can
be affected by external factors like the amount of traffic on the network, the type of
this traffic and the number of devices sharing the media. In a multi-access topology,
nodes are competing for the media, and therefore the available throughput of each
node decreases as the usage of the media increases. In addition, on network with
multiple segments, the throughput cannot be faster than the slowest link. Even if all
Technical Diary – Semester 1
Page 19 of 39
Manuel Munoz Soria – 21076464
the other links have high bandwidth, it only takes one segment with a slow path to
create a bottleneck to the throughput of the entire network.
-Goodput19; this is the amount of usable data transferred to the network user, and is
calculated by subtracting form the throughput the traffic overhead for establishing
sessions, acknowledgements and encapsulation.
The different types of media transmission that we can find are as follows:
za
ud
y.
co
m
-Copper Media; data is transmitted as electrical pulses, and the timing and voltage of
these signals are prone to interferences or ‘noise’ from outside the cables. Radios
waves and electromagnetic devices can create Electromagnetic interferences (EMI)
that can distort and corrupt the data signals. Different types of copper cables use
shielding or twisting the internal pair of wires to minimize signal degradation. 20
At the time of designing a network infrastructure, it is crucial to avoid known sources
or EMI and use cabling techniques that provide proper handling and termination of
the cables.
Unshielded Twisted Pair21 (UTP) cables are generally composed of 6 internal
cooper cables, organised in pair that have been twisted to keep the wires as close to
each other as possible, thus cancelling the signals caused by electromagnetic
interference of external sources. This cancellation provide by the twist also helps
avoid and effect called Crosstalk, where the interferences are generated by the
magnetic field around the adjacent pairs of wires in the cable.
IEEE rates the UTP cabling according to its performance22, creating categories
based on the ability of the cable to carry higher bandwidth rates. For example
Category 5 (Cat5) is used commonly in 100BASE-TX installations, while Enhanced
Category 5 (Cat5e) or Category 6 (Cat6) are for 1000BASE-TX installation where
data transmitted over the media can reach 1Gigabyte of bandwidth.
A derivation cable of UTP standard is called STP (Shielded Twisted Pair)
where the wires are wrapped in a metallic braid or foil. STP provides better noise
protection than UTP cabling, but it also has a higher price. The new 10 GB standard
for Ethernet has a provision of using STP cabling.
Coaxial cable is another type of cooper media, used mainly for high radio
frequency signals like cable television. In the past coaxial cables was used in Ethernet
installations, but today UTP offers lower cost and higher bandwidth than its
predecessor.
STP CABLE
na
UTP CABLE
COAXIAL
23
The ISO 887724 specified RJ-45 connector to be used for a range of Physical Layer
specifications, one of which is Ethernet. Another specification, EAIA-TIA 568
describes the colour codes for Ethernet straight-through and crossover cables.
Technical Diary – Semester 1
Page 20 of 39
Manuel Munoz Soria – 21076464
The picture on the left hand side shows the two
different ends standard for a RJ45 Ethernet cable.
It is essential to ensure all cooper media terminations
are of high quality perform and tested to ensure
optimum performance.
m
25
na
za
ud
y.
co
-Wireless Media26; it carries the electromagnetic signal at radio and microwave
frequencies over the air. Wireless communications are therefore highly susceptible to
electromagnetic interferences, buildings, walls and also certain materials like steel
that reflect the waves. The benefits of wireless are the mobility of host that the
coverage provides and the cost saving at the time of deploying installations in difficult
locations were the use of wiring will be expensive.
A major issue with wireless communications is security27, because virtually
anybody can access the media as it travels through the air, capturing the waves and
decoding them. It is the job of the network administrators to monitor and encrypt the
data as it is transmitted, protecting the Wireless LANs from unauthorised access.
The IEEE created four common data communications standards for wireless,
and these are:
-Standard IEEE 802.1128; this is the wireless LAN that uses a contention or nondeterministic system with a Carrier Sense Multiple Access/Collision Avoidance
(CSMA/CA). This standard has develop on others that may not be compatible to each
other, these others29 are:
802.11a; operates at 5GHz frequency and provides up to 54Mbs bandwidth.
Because it operates at higher frequencies, this standard has a small coverage area and
is less effective at penetrating building structures. Devices operating at this standard
are not compatible with the devices of standards 802.11b and 802.11g.
802.11b; operates at 2.4 GHz and offers up to 11 Mbps bandwidth. It provides
a longer coverage area and is better at penetrating building than 802.11a is.
802.11g; operates at the same frequency that 802.11b (2.4 GHz) but offers 54
Mbps of bandwidth instead, the same figure that 802.11a offers.
802.11n; this standard is currently in draft, and the proposed frequency for it
will be 2.4GHz or 5 GHz, with data rates of 100 Mbps to 210 Mbps and a coverage
range of up to 70 meters.
-Standard IEEE 802.1530; this is the standard Wireless Personal Area Network
(WPAN), commonly known as ‘bluetooth’. It uses a device pairing process to
communicate from a distance up to 10 meters.
-Standard IEEE 802.16; is known as WiMAX (Worldwide Interoperability for
Microwave Access), and uses a point-to-multipoint topology to provide wireless
broadband access.
-Global System for Mobile Communications (GSM); implements the Layer 2 General
Packet Radio Service (GPRS) protocol that provides communication over mobile
telephony networks. Other protocols, including GPRS, also enable satellite
communications between earth stations and satellite links.
Technical Diary – Semester 1
Page 21 of 39
Manuel Munoz Soria – 21076464
na
za
ud
y.
co
m
-Fiber Media31; they are capable of very large data bandwidth, and they uses either
glass or plastic fibers to transfer light impulses where the bits are encoded. Because
they are not electrical conductors, this media is immune to electromagnetic
interference and can operate at much greater distances than cooper media without the
need for signal regeneration.
Optical Fiber is generally used as a backbone cabling for high-speed-transfer.
It is more expensive than cooper media and the light pulses are generated either by
lasers or light emitting diodes (LEDs). Electronic semi-conductor devices called
photodiodes32 detect the light pulses and convert them to voltages that can then be
reconstructed into data frames. Fiber optic cables can be classified in two types33:
a. Single Mode is when the cable carries a single ray of light. This type of unidirectional cable can transmit optical pulses for very long distances, but because light
can only travel in one direction over the optical fiber, two fibers are required on the
cable to support full duplex operation.
b. Multimode is when the LED emitter enter the fiber at different angles, this cause
the pulses becoming blurred at the receiving end, creating an effect known as modal
dispersion, which limits the length of multimode fiber segments.
The termination of the fiber cable requires special training and equipment. The three
common errors of fiber optic34 cable termination are:
-Misalignment, when the fibers are not aligned with each other when joined.
-End gap, when the media do not completely touch at the splice or connection.
-End finish, when the media terminations are dirty or not well polished.
It is therefore highly recommended to use an Optical Time Domain Reflectometer35
(OTDR) to inject a pulse of light into the cable and test the media. The OTDR can
also calculate the approximate distance at which these faults are detected along the
length of the cable.
The following pictures represent some common Fiber Media Connectors. Note that
LC stands for Lucent Connector.
Technical Diary – Semester 1
Page 22 of 39
Manuel Munoz Soria – 21076464
m
za
ud
y.
co
2. Data Encoding. Encoding is the method of converting a stream of bits into a
predictable pattern, distinguishing data bits from control or error detections bits, so
that can the stream of bits ca be recognised by both the sender and the receiver.
Coding groups36 is the method of using a number of bits to represent a data
value, indicating for instance the start or end of a frame, or representing the data value
0011 as the code group 10101. This method helps detect error more efficiently,
especially as data transmission rates speed increases, and although the use of coding
groups introduces overhead in the form of extra bits to be transmitted, they improve
the reliability of the communication. This is particularly true for higher speed
transmissions.
Some of the advantages of using code groups are:
Reduction of bit level error37; the transmission needs to be synchronise from sender to
receiver, in order to sample the signal into the media. Transmission of groups of data
bits allows of minor error in synchronisation, ensuring that the sequence of bits will
be interpreted correctly at the other end.
Limitation of the energy transmitted; group coding balance the process of transmitting
1s and 0s, preventing the media of overheating is lots of 1s are sent.
Distinction between data bits and control bits; the code groups have three types of
symbols that represent the bits: data, control and invalid symbols.
Better media error detection; this is achieved by using the invalid symbols. If received
the Physical Layer can determine that an error has occur during transmission.
na
3. Signalling. This is the method of representing the values ‘1’ or ‘0’ on the media,
this representation is achieved by changing one or more of the Amplitude, Frequency
or Phase of the signal. For the transmission to work there needs to be some sort of
clock between sender and receiver to maintain synchronisation. There should be as
well a signalling method agreed to be used between the ends, so that the signal can be
detected and decoded properly. Two common signalling methods are:
NRZ Signalling 38(Non Return to Zero); a low voltage on the signal represents a 0,
and a high voltage value represent a 1. This method is only suited for slow data links,
because NRZ signalling uses bandwidth inefficiently and is susceptible to
electromagnetic interference.
Manchester Encoding39; this signalling method represent the values as voltage
transition, from low to high represents the value of 1 and from high to low is 0.
Manchester Encoding is the signalling method used in 10BaseT, running at 10 Mbps.
In Chapter 9 we study Ethernet, the predominant LAN technology in the world.
The success of Ethernet is because of its simplicity and ease of maintenance, the
Technical Diary – Semester 1
Page 23 of 39
Manuel Munoz Soria – 21076464
m
ability to incorporate new technologies, its reliability and the low cost of installations
and upgrades.
It operates at the lower two layers of the OSI Model, performing a key role in
the communication that takes place between devices. For Ethernet, the IEEE 802.2
standard40 describes the Logical Link Control (LLC) sublayer functions, while the
802.3 standard describes the Media Access Control (MAC) sublayer and the Physical
Layer functions.
ud
y.
co
The Ethernet MAC sublayer has two primary functions: Data Encapsulation (provides
addressing and error detection) and Media Access Control (control the placement of
frames on the media).
The logical topology of Ethernet is multi-access bus, in which all the devices
in the network share the media, thus receiving each one of them all the frames
transmitted by the others. The examination of MAC address is use to determine if the
node needs to process the receiving frame. Ethernet uses the method Carrier Sense
Multiple Access with Collision Detection (CSMA/CD) to define how devices can
access the media.
na
za
- Encapsulating the Packet. There are two styles of Ethernet frames, the original IEEE
802.3 and the revised IEEE 802.3 that includes the addition of a Start Frame Delimiter
(SFD) field. The original Ethernet frame has a minimum frame size41 of 64 bytes and
a maximum of 1518 bytes. The IEEE 802.3ac standard, release in 1998, extended the
maximum frame size to 1522 bytes to accommodate emerging technologies like
Virtual Local Area Network (VLANs). If the size of the transmitted frame is less than
the minimum or greater than the maximum, the frame is dropped and collisions are
likely to occur.
The following image displays the fields of an Ethernet frame:
-Preamble and Start Frame Delimiter Fields; used for synchronization between the
sending and receiving devices.
-Destination MAC Address Field; contains the MAC address of the intended
recipient.
-Source MAC Address Field; contains the MAC address of the original sender.
-Length/Type Field; defines the exact length of the frame’s data field, ensuring that
the message is received properly. When a node received a frame, it examines the
length-type frame field and if the value is equal to or greater than 0x6000
hexadecimal or 1536 decimal, then the contents of the data field are decoded
according to the protocol indicated.
Technical Diary – Semester 1
Page 24 of 39
Manuel Munoz Soria – 21076464
-Data and Pad Fields; between 46 and 1500 bytes, it contains the data encapsulated
from a higher layer.
-Frame Check Sequence Field; is used to detect errors in the frame by using a Cyclic
Redundancy Check (CRC) generated by the receiver.
co
m
-Ethernet MAC address. It is a 48-bit binary value expressed as 12 digits
hexadecimal, and is added as part of the Layer 2 PDU. It is burn into the ROM of the
device and therefore cannot be changed. IEEE assign to each vendor of devices a 3byte code called the Organisationally Unique Identifier (OUI), and each device must
use that vendor assigned OUI42 as their first 3 bytes. In addition, all MAC addresses
with the same OUI must be assigned a unique value in the last 3 bytes, representing
the vendor serial number.
ud
y.
A representation of the Hexadecimal
Number values is displayed on the table
on the left hand side.
Hexadecimal is technically represented in
text with the value preceded by ‘0x’.
Therefore to represent the hexadecimal
value of 73, we will write 0x73.
Hexadecimal is used to represent MAC
Addresses and IP Version 6 addresses.
na
za
-Current Ethernet. In the old days the central point of a network segment was a hub,
and the risk of collisions increased as the number of device connected. With the
introduction of switches the number of collisions is greatly reduced. Switches can
control the flow of data by isolating each port and sending a frame only to its proper
destination, instead of sending the frame to all the ports like hubs do. This and the
introduction of full duplex communications, where the media transfer both
transmitted and received signals at the same time, has enable the development of
1Gbps Ethernet and beyond.
Ethernet uses Carrier Sense Multiple Access with Collision Detection
(CSMA/CD) to detect and handle collisions. With this method, all devices have to
listen before transmitting. It may occur that the distance between devices is such that
both will start to transmit unaware of each other transmission. The amount of time it
takes to the signal to propagate across the media is called latency.
When a collision is detected, the devices involved in the collision send a jamming
signal43 to notify the others, so that they will invoke a back off algorithm. The jam
signal is 32-bit length, and this back off algorithm causes the devices to stop
transmitting for a random amount of time, to allow the collision signal to subside.
After this random back off time expires, the devices go into the ‘listening before
transmitting’ mode.
Technical Diary – Semester 1
Page 25 of 39
Manuel Munoz Soria – 21076464
co
m
In Ethernet with speed of 10 Mbps, the sending device transmits 64 bits of timing
synchronisation knows as Preamble, meaning that each receiving device will use 8
bytes of this timing information to synchronise with the circuit. Ethernet
implementations with 100 Mbps throughput or more re synchronous and do not need
the timing information, but for compatibility reasons. The Preamble and Start Frame
Delimiter (SFD) are still present on the frames.
Slot time is an important parameter to determine how many devices can share a
network on half-duplex Ethernet. The slot time for a 1000 Mbps Ethernet is 4096 bit
times or 512 octets; this slot time ensures that is a collision is going to occurs, it will
be detected within the first 4096 bits (512 for a 100 Mbps Ethernet) of the frame
transmission.
Interframe Spacing. Once a frame has been sent, the devices are required to wait a
minimum of 96 bit (9.6 microseconds) before transmitting again. This interframe
space reduces as the Ethernet speed increases, a for a 1 Gbps Ethernet is 0.096
microseconds.
na
za
ud
y.
-Types of Ethernet44t. 10 Mbps Ethernet or 10BASE-T is generally no longer used for
LAN installations. The most popular are the 100 Mbps (Fast Ethernet) and the 1000
Mbps (Gigabit Ethernet). The 10 Gbps Ethernet is not fully implemented in small
networks.
100 Mbps – Fast Ethernet; if it uses Cat5e or Cat6 cooper media is known as
100BASE-TX, and if it used fiber media is known as 100BASE-FX. Because of the
higher frequency signals used in Fast Ethernet, the transmission are more susceptible
to noise, and therefore two separate encoding are used by 100 Mbps Ethernet to
enhance the signal.
1000 Mbps – Gigabit Ethernet; due to its speed, on this Ethernet timing is critical,
and its performance depends on how fast devices can detect voltages levels and how
reliable the signal is. The types of Gigabits Ethernet are based on the media used.
1000BASE-T Ethernet provides full-duplex transmission using Cat5e or later media.
It uses an encoding scheme called 4D-PAM5 that enables the transmission of the
signal over the 4 pair of wires simultaneously. This allows the transmission and
reception of data in both directions and at the same time. 1000BASE-T uses many
voltage levels, nine on idle periods and up to 17 when transmitting, this makes the
transmission more susceptible to noise due to cable and termination problems.
1000BASE-SX and 1000BASE-LX Ethernet used Fiber optics cables, providing noise
immunity, small physical size and increased unrepeated distances. The transmission
code is based on the 8B/10B encoding scheme and the principal differences between
SX and LX fiber versions are the media, connectors and wavelength of the signal.
-Switches and Hubs45. Hubs do not perform any type of traffic filtering and some of
the issues of having a hub based network are scalability, latency (each other had to
wait for an opportunity to transmit in order to avoid collisions), network failure (if a
device creates detrimental traffic, the communication for all devices will be affected)
and collisions
Switches, on the other hand, allow the segmentation of the LAN into separate
collisions domains. They improve the throughput of a network because each node has
a full media bandwidth available for itself; they provide a collision-free environment
and full-duplex operation. Before switches existed, Ethernet was half-duplex only.
Selecting Forwarding is the process by which switches forward individuals
frames from a receiving port to another port where the destination devices is
Technical Diary – Semester 1
Page 26 of 39
Manuel Munoz Soria – 21076464
co
m
connected. This is achieved by the means of a MAC tables that the switches
maintains. The switch will look in this MAC table for the MAC address
corresponding to the destination MAC address of the packet it needs to forward. To
accomplish their purposes, switches use five basic operations:
-Learning; the MAC address is populated as the activity in the switch increase and
frames are travelling in and out.
-Aging; the entries in the MAC address have got a timestamp when they are created,
and old entries are removed accordingly.
-Flooding; if the switch doesn’t know what port to send the frames, it sends it to all
ports except the one that sends it.
-Selective Forwarding; this is the process of sending a frame to a port where the
switch knows the destination host resides.
-Filtering; switches will drop frames based on filters like frames with bad CRC,
corrupted or blocked by security settings.
ud
y.
-ARP Process46. Address Resolution Protocol is responsible of maintaining ARP
tables, where MAC addresses are mapped to IPv4 addresses, and are use by the Data
Link Layer and the Network Layer to determine the destination of the frame.
ARP tables are maintaining dynamically and are populated either by
monitoring the traffic that occur on the local network segment or by devices that
request an ARP request by broadcast. The entries on the ARP tables are also
timestamp, like in the MAC tables, and they are deleted if they are no in used for a
while. Static ARP entries do not expire and must be deleted manually.
If a node sends an ARP request47 looking to map a MAC address to an IPv4
address outside its network, the router uses a process called Proxy ARP, acting as the
original sender of the request and, in a way, faking the identity of the original sender.
By default, Cisco routers have Proxy ARP enable on all LAN interfaces.
ARP spoofing and ARP poisoning and techniques used by intruders to inject
wrong MAC addresses to a network, generating fakes ARP requests. To increase the
security, manually configured static ARP can be used as well as restricting the
network access by MAC filtering to only the devices listed on the ARP tables.
za
2. References
1
Data Link Layer Definition http://www.linfo.org/data_link_layer.html [Accessed 4 February 2010]
CCNA Study Notes – Data Link Layer http://www.defoenet.com/ccna/osi_l2.html [Accessed 4 February 2010]
3
The TCP/IP Guide – Data Link Layer http://www.tcpipguide.com/free/t_DataLinkLayerLayer2.htm [Accessed 4
February 2010]
4
IEEE 802.3 Logical Link Control http://www.erg.abdn.ac.uk/users/gorry/eg3567/lan-pages/llc.html [Accessed 4
February 2010]
5
Media Access Control – Wikipedia http://en.wikipedia.org/wiki/Media_Access_Control [Accessed 4 February
2010]
6
Data Link Layer and IEEE http://www.comptechdoc.org/independent/networking/guide/netieee.html [Accessed 4
February 2010]
7
Carrier Sense Multiple Access http://www.linktionary.com/c/csma.html [Accessed 4 February 2010]
8
Network Topologies Examples http://compnetworking.about.com/od/networkdesign/a/topologies.htm [Accessed
4 February 2010]
9
Webopedia: Network Topologies http://www.webopedia.com/quick_ref/topologies.asp [Accessed 4 February
2010]
10
Picture from the Internet http://3.bp.blogspot.com/_hUhsuAxPSU/Rm0lCiElztI/AAAAAAAAAAs/LSo9S1Jiqos/ [Accessed 5 February 2010]
11
Ethernet – The Wireshark Wiki http://wiki.wireshark.org/Ethernet [Accessed 5 February 2010]
12
Cyclic Redundancy Check http://en.wikipedia.org/wiki/Cyclic_redundancy_check [Accessed 5 February 2010]
13
OSI Layer 2 Protocols http://netcert.tripod.com/ccna/internetworking/layer2.html [Accessed 5 February 2010]
14
IEEE 802.3 Ethernet Working Group http://www.ieee802.org/3/ [Accessed 6 February 2010]
na
2
Technical Diary – Semester 1
Page 27 of 39
Manuel Munoz Soria – 21076464
15
na
za
ud
y.
co
m
Internet Engineering Task Force http://en.wikipedia.org/wiki/Internet_Engineering_Task_Force [Accessed 8
February 2010]
16
OSI Model Physical Layer One
http://compnetworking.about.com/od/basicnetworkingconcepts/l/blbasics_osi1.htm [Accessed 8 February 2010]
17
Bandwidth Explained http://www.christianwebmaker.com/articles/bandwidth.html [Accessed 8 February 2010]
18
Bandwidth, Throughput and Goodput
http://www.callcentermagazine.com/shared/forum/showTopics.jhtml?sid=8&fid=701042 [Accessed 8 February
2010]
19
Goodput Facts http://www.absoluteastronomy.com/topics/Goodput [Accessed 8 February 2010]
20
AP Dubey. Networking Tutorial for beginner and advanced user. http://techraga.com/category/basics-ofnetworking/ [Accessed 10 February 2010]
21
CCNA: Network Media Types http://www.ciscopress.com/articles/article.asp?p=31276 [Accessed 10 February
2010]
22
Network Cable Types and specifications
http://www.techotopia.com/index.php/Network_Cable_Types_and_Specifications [Accessed 10 February 2010]
23
Jobstown Networking. UTP, STP and Coaxial images source http://networking.jobstown.net/cable.html
24
ISO/IEC 8877 http://www.iso.org/iso/catalogue_detail.htm?csnumber=21311 [Accessed 10 February 2010]
25
RJ45 Standard Terminations picture source.
http://eduaraul.spaces.live.com/blog/cns!2C5731F99B07D172!801.entry [Accessed 10 February 2010]
26
HowStuffWorks – How WiFi Works http://www.howstuffworks.com/wireless-network.htm [Accessed 12
February 2010]
27
Wireless Security Explained http://www.moneysupermarket.com/c/broadband/wireless-security/ [Accessed 12
February 2010]
28
802.11 Wireless http://en.wikipedia.org/wiki/IEEE_802.11 [Accessed 12 February 2010]
29
Wireless Standards http://compnetworking.about.com/cs/wireless80211/a/aa80211standard.htm [Accessed 12
February 2010]
30
IEEE 802.15 Wikipedia http://en.wikipedia.org/wiki/IEEE_802.15 [Accessed 12 February 2010]
31
Optical Fiber Wikipedia http://en.wikipedia.org/wiki/Optical_fiber [Accessed 14 February 2010]
32
Photodiode Definition http://www.answers.com/topic/photodiode [Accessed 14 February 2010]
33
Fiber Optic Cable Single-Mode Mult-Mode Tutorial http://www.arcelect.com/fibercable.htm [Accessed 14
February 2010]
34
Fiber Optics Basis http://www.althosbooks.com/fiopba.html [Accessed 14 February 2010]
35
Optical time-domain Reflectometer http://en.wikipedia.org/wiki/Optical_time-domain_reflectometer [Accessed
14 February 2010]
36
Data Encoding Techniques http://www.rhyshaden.com/encoding.htm [Accessed 14 February 2010]
37
Error detection and correction http://en.wikipedia.org/wiki/Error_detection_and_correction [Accessed 14
February 2010]
38
Non-return-to-zero – Wikipedia http://en.wikipedia.org/wiki/Non-return-to-zero [Accessed 14 February 2010]
39
Manchester Encoding http://www.erg.abdn.ac.uk/users/gorry/course/phy-pages/man.html [Accessed 14
February 2010]
40
What is IEEE 802 standards? http://www.webopedia.com/TERM/I/IEEE_802_standards.html [Accessed 14
February 2010]
41
How a LAN Switch Works > Frame Size http://www.informit.com/articles/article.aspx?p=357103&seqNum=3
[Accessed 18 February 2010]
42
Ethernet MAC Address Assignments http://www.erg.abdn.ac.uk/users/gorry/course/lan-pages/mac-vendorcodes.html [Accessed 18 February 2010]
43
Jam Signal – Wikipedia http://en.wikipedia.org/wiki/Jam_signal [Accessed 18 February 2010]
44
Ethernet Tutorial http://compnetworking.about.com/od/ethernet/l/aa102900b.htm [Accessed 18 February 2010]
45
What is the Difference between a hub and a switch? http://www.duxcw.com/faq/network/hubsw.htm [Accessed
18 February 2010]
46
ARP Process http://technet.microsoft.com/en-us/library/cc940010.aspx [Accessed 18 February 2010]
47
How ARP Works http://www.tildefrugal.net/tech/arp.php [Accessed 18 February 2010]
3. Straightforward and Difficulties
At this point of the course I can say with confidence that I am sure I will pass
this semester. After the big obstacle that was chapter 6, I am finding the other
chapters not very difficult to understand, though I want to make clear they are not
easy either. It is true that the more we dig into the course, the more the materials that
we are learning relates to each other and the more everything is starting to make sense
as a whole. That helps the growth in my confidence, which in returns brings me even
more confidence, thus making me easy to take full control over this course. The
routine that the teacher has setup for us (power point presentation, questions, exams
Technical Diary – Semester 1
Page 28 of 39
Manuel Munoz Soria – 21076464
m
and then practical) is really good and definitely works to help you understand the
relevant chapter with a minimum attention.
It seems to be that the contents of this Cisco course are being design to really
scrutinise every singles aspect of a network. It studies in detail the functions of every
field we go through with an engineering mind, making difficult the learning process
because I get lost in the details very often. The terminology associated with the
aspects of the course is very complex as well, and because everything is new it takes
time to assimilate and try to memorise everything. I realised more and more that this
is a technical course, and therefore the curriculum is always going to be technical, full
of acronyms, calculations, numbers and mathematics. There is no Plug-And-Play
button on the Cisco course.
ud
y.
co
4. Strategies
I have continued firm on my decision for working all Saturday mornings,
either at home or at the University, and the results are evident to my point of my in
relation with the Cisco course. Though not all the time I turn up for the Wednesday
lessons having read all the material, I always attend with confidence and whishing to
learn because in a way I have done my bit on Saturday, developing this Diary and
reading.
Practical on Cisco are the area where I am feeling weak. We do practical every
Wednesday, but this is the only time a week that I dedicate to this important area of
the course. I do have Packet Tracker at home, the Cisco program to create practical
exercises, but do not really know how to use it and have done very little of the
practical exercises that the online course recommend us to do every week. I still have
to develop a strategy to be able to do the practical exercises of this course with certain
level of confidence.
na
za
5. Reflections
After the black hole of Chapter 6 and the bad beginning that I had on doing the
exam for Chapter 7 (I scored for the first time on this course less than the passing
mark of 70%), things are beginning to take shape again and I am trying to cope with
this course a bit better. The material to learn is now denser and complex than ever, the
researches that I have to do to create this Diary involves lots of reading and analysing.
There is virtually not enough time to process all the information that we are learning,
especially when you work full time. Time is always the decisive factor: the more you
put into it, the better the course evolves.
There is not doubt that whoever design the course material presentation need
to have a second thought about it. Chapter 8, the types of media used on a network,
should have been given to us at the beginning of the course, so that we can start
building from that. The pieces of each chapter are related to each other, I can see that
now, but definitely they are not in the order I would have chosen at the time of
showing these somehow complex concepts to a student.
And the Packet Tracer is becoming an issue now. Still, well into the course
process, Packet Tracer has not been installed on the labs where our course takes place.
The practical are very good and instructive, but they will be brilliant if we dedicate a
few minutes to replicate the problems using Packet Tracer, so that we can start
learning how to use the software and use it at home for testing.
Technical Diary – Semester 1
Page 29 of 39
Manuel Munoz Soria – 21076464
Part 4 [Chapters 10 and 11]
ud
y.
co
m
1. Technical Content
Chapter 10 was focus on planning and cabling networks and we study in this
chapter the different devices that make up a network.
The primary Internetwork device is the router1, which is used to connect networks
to one another, delimiting the broadcast domains. Then the switch is use to connect
the network internally, segmenting the network into collision domains.
Factors that need to be analysed at the time of buying a switch and its speed, the
number of ports and the management capabilities like security and advanced features.
Other considerations are redundancy, if we want to provide it, the expansion modules
or fiber ports needed. Using a simple ‘cost per port’ calculation is a way to approach
the investment, and it is recommended to buy small switches connected to a main one
rather than a massive one single switch where everything is connected.
Factors to be considered when buying a router and similar to those of the
switches, however we have to think carefully about the expandability, the modular
devices that we want to connect and the number of networks the router will support,
and the operating system features, which determine what sort of extra services the
router will provide2, like VPN security, Quality of Service, Voice over IP, Dynamic
Host Control Protocol, etc. Routers are generally more expensive than switches, and
its purchase have to be consider carefully.
na
za
-Interconnecting Devices. The main factor to consider when joining interconnecting
devices is the type of media to use. We should avoid attenuation3, the reduction of the
signal strength as it moves down the media: the longer the media the more attenuation
the signal will have. Cabling distance is therefore a critical factor, and other things to
considerer when choosing a type of media is the cost of the media itself (fiber is more
expensive than UTP), the bandwidth that the media will provide, the easy of
installation and the susceptibility to the media of Electromagnetic Interferences
(EMI).
When planning the installation of a network4, there are four physical areas to
consider:
Technical Diary – Semester 1
Page 30 of 39
Manuel Munoz Soria – 21076464
m
-The Work Area. The UTP cable in this area, called patch cable, should not extend 10
meters, and normally it connects the wall jack to the computer using a straightthrough cable.
-Horizontal Cabling. The maximum length on the cable in this area should not extend
90 meters, and this distance is referred as the permanent link because it is installed
with the building structure and normally is not changed or upgraded.
-Telecommunications Room; this is where the routers, switches and servers will
reside. For UTP the recommended length of the cable to connected devices on the
telecommunications room is up to 5 meters.
-Backbone Cabling; is the link that connects the telecommunication room to other
telecommunications rooms, where more servers could be located, or to a WAN
connection or ISP.
na
za
ud
y.
co
-RJ-45 Connection; in an Ethernet LAN, devices use one of two types of UTP
interfaces, MDI or MDIX5. In MDI (Media-Dependent Interface), pins 1 and 2 are use
for transmitting, while pins 3 and 6 are used for receiving.
For MDIX (Media-Dependent Interface Crossover), the transmitting pairs are
swapped internally, thus allowing similar devices to connect to each other.
Straight-Through cables have the connector on each end terminated exactly the same;
they both can be either standard T568A or T568B6. This cable is use to connect
different devices to each other, like switch to a router, computer to switch or computer
to hub.
Crossover cables have got one terminated with the T568A standard and the other with
the T568B standard. They are use to connect similar devices like from switch to
switch/hub or hub to hub/switch, as well as router to router Ethernet port connections,
computer to computer and computer to router Ethernet.
Technical Diary – Semester 1
Page 31 of 39
Manuel Munoz Soria – 21076464
co
m
Many devices have a mechanism that electrically swap the transmitting and receiving
pairs, their ports functions as MDI or MDIX and are not affected by the type of cable.
-WAN Connection; The typical cable7 use to connect Cisco router to a wan connection
is a serial cable with one end using a Winchester 15 pin connector (that can be male
or female) and the other end using a smart serial DB-60 connector.
ud
y.
The communication via a WAN connection needs one of the ends to provide a
clock8 in order to maintain synchronisation of the data transferred. The clock rate
needs to be acceptable for both the sending and receiving device, and normally the
synchronisation clock is provided by the ISP end. Care has to be taken at the time of
connecting the serial cable to the router, to determine which end will provide the
clock. DCE (Data Communications Equipment) is the device that supplies9 the clock.
DTE (Data circuit-Terminal Equipment) is the device that receives the clocking.
The V.35 compliant router cables are available in DTE and DCE versions.
Devices network interfaces normally do not have keyboard, mouse or
monitors. To connect to them we use programs called Terminal Emulator, connecting
to the network device often via a serial or console cable.
na
za
There are many reasons to divide a network into subnets, to manage broadcast
traffic, for security or for different network requirement on each subnet. We need to
be aware of all the possible devices that will require an IP address, like switches and
wireless access points.
To allocate IP addresses to a network there are two main methods, we can use
the Variable Length Subnet Masking (VLSM) when we divide the networks
depending on the numbers of host that each one of them will contain, or we can use a
non-VLSM approach, where all the subnets use the same prefix length and number of
host bits.
Chapter 11 involved configuring and testing the network; we leant during
this chapter about the Cisco Internetwork Operating System10 (IOS) that is use in the
Cisco devices to provide the following network services:
-Basic routing and switching functions
-Reliable and secure access to networked resources
-Network scalability
The services provided by the IOS are generally accessed using a Command Line
Interface11 (CLI). Using flash memory allows the IOS to be upgraded to newer
versions or to have their features improved. In many Cisco routers, the IOS is copied
into RAM when the device is power on, and then it runs from the RAM; this is done
by design to increase the performance of the device. There are several ways to access
the CLI environment, the most common methods are:
Technical Diary – Semester 1
Page 32 of 39
Manuel Munoz Soria – 21076464
ud
y.
co
m
-Console; it use a low speed serial cable connected directly to a compute, and
the console port is the management port that provides out-of-band access to a router.
The connection to the console port is know as the CTY, and is accessible even if no
networking services have been configured on the device. Normally, when a router is
first place into service, the console port is use to configure the device. Though to
access the console port, an intruder has to be physically connected to the router and by
pass the security of the building or whichever location the router is installed, it is
recommended to setup a password to access the console port.
-Telnet and SSH; Telnet12 is use to access remotely a router and open a CLI
session. Connections using telnet are known as VTY, and they require one active
interface to access the device through the network. Secure Shell Protocol (SSH) is a
more secure method of accessing the device remotely, it provides stronger password
authentication than telnet and it uses encryption when transferring the data. For
security reasons, the IOS requires that all telnet connections to the router use a
password. Newer IOS contains the facility to connect to the router using SSH, though
this service may have to be enable.
-AUX; Another way to establish a CLI session remotely is via a telephone line
connected to the AUX port of the router. Like the console port, the AUX port does not
need any configuration or active network connection in the router. In addition, the
AUX port can also be used locally like a console port.
za
Configuration files contain the IOS software commands that are use to
customise and configure the Cisco device. Commands are parsed (translated and
executed) by the IOS when the system is booted from the startup-config file, or when
commands are entered in the CLI by the administrator. A Cisco network device
normally contains two configuration files:
-Start-up Configuration file (startup-config) is stored in the non-volatile RAM
(NVRAM) and is loaded into memory when the device is started. Because the
NVRAM will keep the configuration file even if the power if off, the startup-config
file is use as well as a backup of the configuration device.
-Running Configuration file (running-config); once in memory, the startupconfig becomes the running-config and is use to operate the network device. Changes
to the running configuration will take effect immediately; however we have to save
the changes from the running-config to the startup-config, so that the changes are
saved into the NVRAM and are loaded next time the router reboots.
na
The Cisco IOS is design as a modal operating system13, with different modes
of operations that grant different access at the time of configuring the device. The
most common operation modes for the IOS are:
-User Executive Mode [Router>] has limited capabilities but is useful for some
basic operations. By default there is no authentication required to access the User
Exec Mode, but it is a good practice to ensure that a password is configured.
-Privilege Executive Mode [Router#] only administrators should access this
mode, because the Privilege Exec Mode allows the execution of configuration and
management commands. By default, this mode does not prompt for authentication,
and it is crucial that a password is configured to access this Privilege Exec Mode.
When using CLI, you should type ‘enable’ or ‘disable’ to switch from User Exec
Mode to Privilege Exec Mode.
-Global Configuration Mode [Router(config #] can only be reached from the
Privilege Exec Mode, and is use for specific configuration of the device. Changes
Technical Diary – Semester 1
Page 33 of 39
Manuel Munoz Soria – 21076464
ud
y.
co
m
made to the device during this mode will affect the operation of the unit as a whole, or
just the particular interface we are configuring. To enter Global Configuration Mode
type ‘configure terminal’ in the Privilege Exec Mode.
When using the CLI (Command Line Interface) we are actually accessing the
IOS. To access the CLI Help just enter a question mark (?) at any prompt. Shortcuts
and hotkeys are available, and you could use Ctrl-R to redisplay a line, Ctrl-Z to exit
the current configuration mode, Crtl-Shif-6 to interrupt a process like the ping
command or traceroute and Ctrl-C to abort the current command and exit the
configuration mode. The following graphics shows some of the different variations
the show command could have:
za
-Cisco IOS Good Practices. Some of the best practices for using Cisco products are
the configuration of a hostname, saving the configuration of the startup-config file,
enable password and display an ownership message of the day.
It is recommended to assign a hostname for each networking device,
especially if you are accessing them through Telnet or SSH, in order to avoid
confusion and to follow a naming convention within the organisation. To change the
name of a device, do the following commands:
na
Router#configure terminal
Router#hostname London1
London1#
To remove the name of a device, simply type no hostname in the Global Configuration
Mode.
We need to save the changes made to the device, while working on the Global
Configuration Mode, to the startup configuration file stored in NVRAM. To do the
saving type this commands:
Router#copy running-config startup-config
This will prevent the lost of the modifications made due to power failure or restart. To
remove the configuration and set the device with the manufacture settings, type:
Router#erase startup-config
Router#reload
Technical Diary – Semester 1
Page 34 of 39
Manuel Munoz Soria – 21076464
It is recommended to use authentication passwords for each of the Exec
Modes levels, as well as password to protect specific ports in the device. Whenever
the device supported, we should use the enable secret command, to ensure the
password is encrypted. To configure a password for a console port, type these
commands:
Router(config)#line password 0
Router(config)#password cisco
Router(config)#login
m
In the above example, the password chosen was ‘cisco’. To setup a password for the
five VTY lines, numbered 0 to 4, do the following:
co
Router(config)#line vty 0 4
Router(config)#password cisco
Router (config)#login
Router(config)#enable secret class
Another useful command is password-encryption, to prevent the password showing up
as plain text when viewing configuration files.
It is vital to ensure that we clearly display to anybody attempting to logon to
the system, that only authorized access is allowed. Banners are used for this purpose,
especially the Message of the Day banner, and we should avoid using words like
‘invited’ or ‘welcome’. To configure a MOTD, do the following in Global
Configuration Mode:
ud
y.
Router(config)#banner motd %type your message here%
The delimiter character, in the above example is %, could be anything as long as it
does not appear in the message itself.
-Configuring Interfaces14. By default interface are disabled in routers and enable in
switches. To enable an interface enter the no shutdown command or the shutdown only
if you want to disabled that particular interface. For example, these are the commands
to configure an IP address on an interface of a router:
Router(config)#interface FastEthernet 0/0
Router(config-if)#ip address ip_address netmask
Router(config-if)#no shutdown
za
Router serial interfaces must also have an IP, as well as a clock signal to control the
timing of the communications. Normally the end connected to the ISP will provide the
clock. The following example describes how to configure an IP for a serial interface
and assign a specific clock rate. Note that first of all you have to be on Global
Configuration Mode and then enter the Interface Mode.
na
Router(config)#interface Serial 0/0/0
Router(config-if)#ip address ip_address netmask
Router(config-if)#clock rate 56000
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#
Switches, unless using VLANs for managements purposes, generally do not need to
be assign an IP Address
-Testing the Protocol Stack. The first command we should use at the time of testing
connectivity is the show ip interface brief to ensure the correct IP and Gateway have
been configured. Then we can verify connectivity with commands like ping or
traceroute (this command is called tracert if use within Windows OS command
prompt). The test procedure for the ping command is to ping first of all the local
Technical Diary – Semester 1
Page 35 of 39
Manuel Munoz Soria – 21076464
m
loopback (127.0.0.1), then the local IP Address, then the local Gateway, after that try
to ping a remote host and finally perform a traceroute to that remote host.
If we want to identify physical MAC addresses on the network, we should use
the arp command in the Windows command prompt, particularly the arp –a
combination will show us the arp table for the machine.
Network Baseline15 is the process of studying the network at regular intervals
to ensure that it is working as designed. Creating an effective network performance
baseline is crucial at the time of trying to solve problems, and it is really important to
keep the documentation concerning the network up to date all the time, reflecting on it
whatever changes have been made.
2. References
1
za
ud
y.
co
Router Definition http://www.pcmag.com/encyclopedia_term/0,2542,t%253Drouter%2526i%253D50637,00.asp
[Accessed 21 February 2010]
2
What Advanced Features A Router Can Provide? http://ezinearticles.com/?What-Advanced-Features-Can-aRouter-Provide?&id=2780461 [Accessed 21 February 2010]
3
Attenuation - Wikipedia http://en.wikipedia.org/wiki/Attenuation [Accessed 21 February 2010]
4
Planning a network installation: ICT Hub Knowledgebase
http://www.ictknowledgebase.org.uk/planningnetworkinstallation [Accessed 21 February 2010]
5
Medium Dependent Interface http://en.wikipedia.org/wiki/Medium_dependent_interface [Accessed 21 February
2010]
6
The difference between the TIA/EIA T568A and T568B wiring standards
http://www.duxcw.com/faq/network/diff568ab.htm [Accessed 21 February 2010]
7
Used Cisco Systems Serial Cables http://www.alliancedatacom.com/manufacturers/ciscosystems/connector_cables/serial.asp [Accessed 21 February 2010]
8
Properly set a Cisco router’s clock and time zone http://articles.techrepublic.com.com/5100-10878_116129454.html [Accessed 22 February 2010]
9
DTE and DCE definition http://pinouts.ru/definition/dte-dce.shtml [Accessed 22 February 2010]
10
Cisco Internetwork Operating System (Cisco IOS)
http://www.cisco.com/en/US/products/sw/iosswrel/ps1818/products_tech_note09186a008015083e.shtml
[Accessed 22 February 2010]
11
Introduction to Cisco IOS Software http://www.ciscopress.com/articles/article.asp?p=101658&seqNum=2
[Accessed 23 February 2010]
12
How Telnet Works http://technet.microsoft.com/en-us/library/cc778139(WS.10).aspx [Accessed 23 February
2010]
13
Understand the levels of privilege in the Cisco IOS http://articles.techrepublic.com.com/5100-10878_115659259.html [Accessed 23 February 2010]
14
Cisco IOS Tutorial http://www.cisco.com/warp/cpropub/45/tutorial.htm [Accessed 23 February 2010]
15
Creating a Network Baseline Cisco Tutorial
http://www.thebryantadvantage.com/CreatingANetworkBaseline.htm [Accessed 23 February 2010]
na
3. Straightforward and Difficulties
After the Christmas period, it was with relief to notice that the complexity of
the material we had to learn for this last part of the course was not as hard to digest as
previous chapters. The concepts of Chapter 10, for example, were fairly easy and we
had study some of the serial cables previously on the practical sessions that we did
last year and which are now backing up our knowledge.
However, the Christmas break factor has made this last part of the course
rather difficult due to lost of concentration and a disruption of the learning routine that
the teacher setup for us since October. It has been tricky to achieve the same level of
attention and dedication on the materials for these chapters that I had previously on
other chapters of the course, and I feel that my motivation had decreased. I noticed
that there were not many terms, acronyms or lengthy processes to learn during this
part of the curriculum, however, the practical sessions are now very challenging and
growing in difficulty by the exercise. When we have to connect routers with switches
and issue commands, I had to refer to my notes all the times, and though I enjoy
Technical Diary – Semester 1
Page 36 of 39
Manuel Munoz Soria – 21076464
seeing how at the end of the practical a solution is achieved and the connections are
actually working, I find frustrating the fact that I am still unable to memorise the
majority of the command that we use to configure the Cisco routers and switches.
co
m
4. Strategies
The final exam date is approaching fast, as well as the date to hand out this
Technical Diary. I achieved the lowest mark of this course while doing the exam for
Chapter 11, the one regarding the Command Line Interface for Cisco. I was worry for
this, thinking that perhaps I was not fully prepared for the final exam. This low result
helps me to discover my weakest point (the commands), and it became evident to me
that I had to strength this area of my knowledge, as the final exam surely will be
populated with questions about commands. I started using Packet Tracer at home,
watching videos in You Tube to try to master the program and replicate on it the
problems that we were presented with during the practicals, on Wednesday evening.
It is a shame that Packet Tracer still has not been installed on the labs that we
use for the course, and my main goal during this part of the course was to learn how
to use the program. Lucky for us, Cisco is very popular and there is plenty of help
around the web for this application.
na
za
ud
y.
5. Reflections
We lost the first two Wednesdays of the course due to the snow disruptions,
which made even worse the final come back to the course, right in the middle of
January. It has been very hard to get accustom again and ‘sacrifice’ all Wednesday
evening for the sake of obtaining a Cisco certification and a degree. There is only a
handful of student now, which makes easy the learning in a way (more teaches’ time
dedicated per student) but also put you in the spot quickly if you have not prepare the
lesson as the teacher expects. A couple of times I asked myself during this period
where everybody has gone, why only a few people are doing the Cisco course? And
again my answers were that this is the best course for me to maintain my position in
the IT industry, by gaining intimate knowledge of how a network really works. If not
many people are tempted to do the Cisco course is because of its difficulty. I believe
that the HP variation of this Foundation Degree seems to be easier, and some people
may take it as a shorter route to learn IT.
I am happy to have chosen Cisco, and one of my New Year Resolution for
2010 is to finish successfully this course. There is still a long way to go.
Technical Diary – Semester 1
Page 37 of 39
Manuel Munoz Soria – 21076464
Conclusion
ud
y.
co
m
The process of creating this Technical Diary has been more intense and time
consuming that the Reflective Diary for the Problem Solving Module, which I has
been writing more or less at the same time than this Diary. The fact that this is a
Technical Diary involves lots of researching on the subject for every chapter, reading
complex paragraphs and populating references, some of them really interesting and
others quite boring. All this extreme research has the immediate effect of gaining
knowledge during the process. Without any doubt, this idea of creating a Technical
Diary about the contents that we are learning is for me the best way of learning. It
allows me (force me) to go back to the subject again and again, until the concepts are
really inside my head and given the tick of ‘learnt in detail’.
My score for the Final Exam of this course was 84.6%, and I am very happy to
have passed. I feel I have learnt a lot doing this course, especially by doing the
Technical Diary, which has setup the roots of knowledge into my head. The practical
sessions have contributed as well to my learning, but not in the theory aspects.
The graphic below shows the exams results data of all the tests that I did for
each of the chapters (note that we did not do any test for Chapter 1). It represents in a
graphical mode the learning process that I have experienced while doing this Semester
1 Cisco course. Note that at first I was ok with the material (I really started with high
motivation), then Chapter 6 appeared and I sunk, failing below the passing mark of
70% while doing the exam of Chapter7, because I hardly study anything for this
particular Chapter. I recovered a little bit by the end of the year, showing a more
steady and realistic figures of learning in the exam results, though my performance
overall was not as good as in the beginning. I failed again below the 70% mark during
Chapter 11, just as we came back from the Christmas holidays.
Cisco Exams Semester 1
100.0%
za
90.0%
80.0%
70.0%
60.0%
50.0%
na
40.0%
30.0%
20.0%
10.0%
0.0%
Results
2
3
4
5
6
7
8
9
10
11
80.4%
83.7%
95.1%
97.8%
72.3%
61.1%
82.9%
74.4%
78.4%
57.5%
The table that now follows represents the data from which I have created the
graphic. The source of this data is the ‘Gradebook’ information that monitors the
progress of each student on the NetAcad Cisco website. Notice that, after Chapter 6,
Technical Diary – Semester 1
Page 38 of 39
Manuel Munoz Soria – 21076464
the average score for each part of the course is going down and on the last part (Part
4) my average performance is less than the passing mark of 70%.
Part 3
Average
82.1%
88.4%
72.8%
68.0%
na
za
ud
y.
Part 4
Date Taken
14 October 2009
21 October 2009
04 November 2009
11 November 2009
25 November 2009
02 December 2009
09 December 2009
03 February 2010
03 February 2010
29 January 2010
m
Part 2
Result
80.4%
83.7%
95.1%
97.8%
72.3%
61.1%
82.9%
74.4%
78.4%
57.5%
co
Part 1
Chapter
2
3
4
5
6
7
8
9
10
11
Technical Diary – Semester 1
Page 39 of 39
Manuel Munoz Soria – 21076464