COMPUTER NETWORK
AND DESIGN
CSCI 3385K
Understanding the TCP/IP – Internet Layer
Internet Protocol
• The IP component of TCP/IP determines where packets of
data are to be routed based on their destination address.
• IP uses packets to carry information through the network.
• A packet is a self-contained, independent entity that contains
data and sufficient information to be routed from the source to
the destination without reliance on earlier exchanges.
IP Characteristics
• IP operates at Layer 3 (Network) of the OSI model and Layer 3 of the TCP/IP
(Internet) stack.
• IP is a connectionless protocol in which one-way datagram is sent to the
destination without advance notification to the destination device. The
destination device receive the data and does not return any status information
to the sending device.
• IP uses hierarchical addressing in which the network ID is like a street and the
host ID is like a house or office building on that street.
• IP provides services on a best-effort basis and does not guarantee packet
delivery. A packet can be misdirected, duplicated or lost on the way to its
destination.
• IP does not provide any special features that recover corrupted packets. These
services are instead provided by the end systems of the network.
In real-time voice or video transfers, a few lost packets are tolerable; speed is
more important than packet recovery, because recovering packets would delay
the real-time process.
IP Example: Delivery a letter through a
Postal Service
An analogy of IP service would be mail delivery by postal service.
In this example, you live in San Francisco and your mother lives in
New York. You write three separate letters to your mother. You seal
each letter in a separate envelope, address each letter to your
mother, and write return address in the upper left-hand corner of
each envelope.
You deposit the three letters in the outgoing mail slot at your local
post office. The postal service will make the best attempt to deliver
the three letters to your mother in New York. However, the postal
service will not guarantee that the letters will arrive at their
destination. The postal service will not guarantee that all three letter
will be handle by the same carriers or the same route. Finally, the
postal service will not guarantee that the letters will arrive in the
order in which you mailed them.
IP Addressing
• Facilitates the routing of packets over the network.
• Uses logical addresses known as IP address (32-bit IPv4).
• Every host, computer, networking device, or peripheral
connected to the internet has a unique 32-bit IP address that
identifies it.
• Without structure for allocating all those IP addresses, it
would be impossible to route packets efficiently.
• Learning IP address structure and how they function in the
operation of the network provides an understanding of how IP
packet are forwarded over the networks using TCP/IP
IP Addressing – cont.
• IPv4 address is the most common type of address currently
used on the Internet.
• IPv4 are 32-bit numbers that describe the location of a
network device.
• IP address is a hierarchical address and consist of two parts:
• Network address portion (network ID): describes the network of
which this IP address is a part of. The router maintains information
about routes to each network.
• Host address component (host ID): identifies a specific endpoint.
These endpoints are the servers, computers, and other devices
connected to the network. It is assigned by organizations to
individual devices.
IP Addressing Fields
• As data travels down the protocol stack it is encapsulated.
• At the Internet Layer it is encapsulated into a PDU (commonly
called a packet or datagram)
• The header for this packet has several fields, we will focus on
two of those fields.
• Source Address: Specifies the sending node’s IP address
• Destination Address: Specifies the receiving node’s address
IP Addressing Field – cont.
IP Address Format: Dotted Decimal Notation
• In any given IP address, some portion of the 32-bit number
represents the network and the remaining bits represent the host.
• Many hosts may share the same network address, combining the
network address with a host address uniquely identifies any
device connected to the network.
• 32-bit numbers are broken up into 4 groups of numbers called
octets (1 octet=8 bits)
• Each octet is represented as a decimal number between 0 and 255
and separated by a period. This scheme is known as
“dotted decimal notation” ex:
172.16.128.17 spoken as 172 dot 16 dot 128 dot 17
IP Address Format: Dotted Decimal Notation
IP Address Format: Number Conversion
• Decimal – base 10 (0 through 9) example: 5753
5(thousands) 7(hundreds) 5(tens) 3(ones)
103
102
101
100
• Binary – base 2 (0 and 1) example:
27
26
25
24
23
22
21
20
1
0
1
0
0
0
0
0
128
64
32
16
8
4
2
1
128 + 32 = 160
IP Address Format: Number Conversion
• Binary – base 2 (0 and 1) example:
27
26
25
24
23
22
21
20
1
1
1
1
1
1
1
1
128
64
32
16
8
4
2
1
128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255
IP Address Format: Number Conversion
Example: 168.20.197.137
27
26
25
24
23
22
21
20
1
0
1
0
1
0
0
0
128
64
32
16
8
4
2
1
1010100.00010100.11000101.10001001
128 + 0 + 32 + 0 + 8 + 0 + 0 + 0 = 168 (10101000)
0 + 0 + 0 + 16 + 0 + 4 + 0 + 0 = 20 (00010100)
128 + 64 + 0 + 0 + 0 + 4 + 0 + 1 = 197 (11000101)
128 + 0 + 0 + 0 + 8 + 0 + 0 + 1 = 137 (10001001)
IP Address Format: Number Conversion
Example: 192.168.1.100
27
26
25
24
23
22
21
20
0
0
0
0
0
0
0
0
128
64
32
16
8
4
2
1
11000000.10101000.00000001.01100100
128 + 1 + 0 + 0 + 0 + 0 + 0 + 0 = 192 (11000000)
128 + 0 + 1 + 0 + 1 + 0 + 0 + 0 = 168 (10101000)
0 + 0 + 0 + 0 + 0 + 0 + 0 + 1 = 1 (00000001)
0 + 1 + 1 + 0 + 0 + 1 + 0 + 0 = 100 (01100100)
IP Address Classes
• To accommodate different sizes of network and aid in
classifying them
• IP addresses are divided into categories called classes.
• Assigning IP addresses to classes is known as classful
addressing
• The classes were determined during the early days of the
Internet by the Internet Assigned Numbers Authority (IANA)
• Each IP address is broken down into a network ID and the host
ID. In addition, a bit or bit sequence at the start of each
address determines the class of the address.
IP Address Classes – cont.
Class A
• Class A address uses only the first octet (8 bits) of the 32-bit
number to indicate the network address.
• Remainder three octets of the 32-bit number are used for host
addresses.
• First bit of a Class A address is always 0 and since the first bit
is a 0 the lowest number that can represent is 00000000
(decimal 0) and the highest number can be represented is
01111111 (decimal 127). However, these two network
numbers 0 and 127 are reserved and cannot be used as
network addresses.
• Any address that starts with the value of 1 and 126 in the first
octet represent a Class A address.
Class A
Class B
• Class B address uses two octets (16 bits) of the 32-bit number to
indicate the network address.
• Remainder two octets of the 32-bit number are used for host
addresses.
• First 2 bits of a Class B address are always binary10.
• Starting the first octet with binary 10 ensures that the Class B
space is separated from the upper levels of the Class A space.
• Remaining 6 bits in the first octet may populated with either 1s or
0s.
• Lowest number that can be represented with Class B address is
10000000 (decimal 128) and the highest number that can be
represented is 10111111 (decimal 191)
• Any address that starts with a value in the range of 128-191 in the
first octet is a Class B
Class B
Class C
• Class C address uses three octets (24 bits) of the 32-bit
number to indicate the network address.
• Remainder one octet of the 32-bit number is used for host
addresses.
• Class C address always begins with binary110.
• Lowest number that can be represented with Class C address
is 11000000 (decimal 192) and the highest number that can be
represented is 11011111 (decimal 223)
• Any address that starts with a value in the range of 192-223 in
the first octet is a Class C
Class C
IP Address Ranges
Reserved IP Addresses – Network Address
• An IP address that has binary 0s in all host bit positions is
reserved for the network address:
• Example for Class A, B, and C:
• 10.0.0.0 is the IP address of the network containing the host 10.1.2.3
• 172.16.0.0 is the IP address of the network containing the host
172.16.16.1 (host portion)
• 192.16.1.0 is the IP address of the network containing the host
192.16.1.2 (host portion)
• A router uses a network IP address when it searches its IP
route table for the destination network location
Reserved IP Addresses – Direct Broadcast Address
• To send data to all the devices on a network, a broadcast
address is used.
• Broadcast IP address end with a binary 1s in the entire host
portion (host field)
• Example:
• For network 172.16.0.0 in which last 16 bits represent the host field
the broadcast that would sent out to all devices on that network
would include a destination address of 172.16.255.255
Reserved IP Addresses
Local Broadcast Address
• If an IP device wants to communicate with all devices on the
local network, it sets the destination address to all 1s
(255.255.255.255) and transmit the packet.
• Example:
• Hosts that do not know their network number and are asking some
server for it may use this address.
Local Loopback Address
• A local loopback address is used to let the system send a
message to itself for testing. A typical loopback IP address is
127.0.0.1
Public IP Addresses
• Internet stability depends directly on the uniqueness of
publicly network addresses
• A mechanism is needed to ensure that addresses are in fact
unique.
• Originally this responsibility rested to InterNIC (Inter
Network Information Center)
• Eventually this responsibility was transferred to the IANA
• IANA carefully manages the remaining supply of IP address to
ensure that duplication of publicly used addresses does not
occur.
• Duplication would cause instability in the Internet and
compromise its capability to deliver datagrams to networks
using the duplicate addresses.
Public IP Addresses
• To obtain an IP address or block of addresses, you will need
to contact an ISP (Internet Service Provider).
• Then the ISP will contact their upstream registry or regional
registry at one of the organizations:
• APNIC (Asia Pacific Network Information Center)
• ARIN (American Registry for Internet Numbers)
• RIPE NCC (Reeaux IP Euripeens Network Coordination Centre)
• With the rapid grow of the Internet, public IP addresses
began to run out, so new addressing schemes such as
Network Address Translation (NAT), classless interdomain
routing (CIDR) and IPv6 were developed to help solve the
problem.
Public IP Addresses
Private IP Addresses
• While Internet require a globally unique IP address, private hosts
that are not connected to the Internet can use any valid address, as
long as it is unique in the private network.
• Many private networks exist alongside public networks and
grabbing “any other address” is strongly discouraged.
• Three blocks of IP addresses (one Class A network, 16 Class B
networks, and 256 Class C networks) have been designated for
private, internal use.
• Addresses in this range are not routed on the Internet backbone.
Internet routers are configured to discard private addresses
• When addressing a nonpublic intranet, private addresses can be
used instead of globally unique addresses.
• When a network using private addresses must connect to the
Internet, it is necessary to translate the private addresses to public
addresses. This translation process is NAT and a router is often the
network device that performs NAT (Network Address Translation)
Private IP Addresses
Dynamic Host Configuration Protocol (DHCP)
• DHCP is used to assign IP addresses automatically and to set
TCP/IP stack configuration parameters, such as the subnet
mask, default router, and Domain Name System (DNS)
servers.
• DHCP is also used to provided other configuration
information as necessary, including the length of time the
address has been allocated to the host.
• DCHP consists of two components:
• A protocol for delivering host-specific configuration parameters
from DHCP server to a host
• A mechanism for allocating network addresses to hosts.
Dynamic Host Configuration Protocol – Cont.
• Using DHCP, a host can obtain an IP address quickly and
dynamically.
• It requires a defined range of IP address on a DHCP server
• As hosts come online, they contact the DHCP server and request
address information.
• The DHCP server selects an address and allocates it to that host.
• The address is only “leased” to the host, so that host will
periodically contact the DHCP server to extend the lease.
• The lease mechanism ensures that hosts that have been moved or
are switched off for extended periods of time do not hold to an
address that they do not use.
• Addresses are return to the address pool by the DHCP server to be
reallocated as necessary.
Dynamic Host Configuration Protocol – Cont.
Domain Name System (DNS)
• DNS application provides an efficient way to convert humanreadable names of IP end systems into machine-readable IP
addresses necessary for routing.
• DNS mechanism is to convert symbolic name into IP address.
• DNS application frees users of IP networks from the burden of
having to remember IP address.
• Without this freedom, the Internet would not be as popular or
as usable as it has become.
Domain Name System (DNS) – Cont.
Using Common Host Tools
• Most operating
systems provide a
series of tools that can
be used to verify the
host addressing.
Using Common Host Tools – Cont.
• IPCONFIG used to
display all current
TCP/IP network
configuration values
and refresh DHCP and
DNS setting.
• Use without
parameters, ipconfig
displays the IP
address, subnet mask
and default gateway
for all adapter
Using Common Host Tools – Cont.
Syntax:
• Ipconfig [/all] [/renew [Adapter]] [/release [Adapter]] [/flushdns] [/displaydns]
[/registerdns] [/showclassid Adapter] [/setclassid Adapter [ClassID]]
• /all: displays the full TCP/IP configuration for all adapters
• /renew [Adapter]: renews DHCP configuration for all adapters
• /release [Adapter]: sends a DHCPRELEASE message to the DHCP server to
release the current DHCP configuration and discard the IP address for either all
adapter or a specific adapter
• /flushdns: flushes and resets the content of the DNS client resolver cache. Good
for DNS troubleshooting.
• /displaydns: displays the content of the DNS client resolver cache, which includes
entries, preloaded from the local Host file and any recently obtained resource
records for name queries resolved by the computer
• /registerdns: initiates manual dynamic registration for the DNS names and IP
addresses that are configured at a computer. Good to use when a DNS name
registration failed.