Internet Protocol
© Prof. Aiman Hanna
Department of Computer Science
Concordia University
Montreal, Canada
I nternet Protocol

The Internet
• A WAN consisting of many Networks
• Started in late 1960s when the Advanced Research Project
Agency (ARPA), a part of the U.S. Department of Defense
began funding universities and private organizations for
developing communication systems
• The research led to the creation of the ARPANET network,
which eventually evolved into the Internet
• Today, many would find it impossible to live without the
Internet!
2
TCP/IP

Networks connected to the Internet runs the TCP
(Transmission Control Protocol) / IP (Internet
Protocol) protocols

TCP is a Transport Layer protocol; IP is a Network
Layer protocol

TCP is a connection-oriented protocol

TCP relies on IP to route packets through the network
3
TCP/IP


Two communicating ends run TCP, with which connections are
established (through handshaking) then reliable transfer, data
flow control, …etc. can be enforced
The Network Control Protocol (NCP) was TCP’s predecessor in
the original ARPANET, which was reasonably reliable

When the ARPANET evolved to the Internet, reliability was lost

Consequently, TCP replaced NCP to allow running over
unreliable networks
4
TCP/IP


The User Datagram protocol (UDP) is a Layer 4
alternative to TCP
In contrast, UDP is a connectionless protocol
Figure 11.1 – Internet Protocols
5
TCP/IP


TCP provides reliable connection independent of
underlying network architecture
IP provides the packet delivery service
Figure 11.2 – IP Transmitting over Different Networks
6
I nternet Addressing

To an Internet user, Internet addresses may look like:
Sunset.Concordia.ca
http://www.Microsoft.com

The form also appears on Internet addresses:
Comp445@encs.concordia.ca

These textual representations however are not actual
Internet addresses

Internet Domain: A collection of sites of a particular
type, such as com, org, edu, gov, ...etc.
7
I nternet Addressing

How this textual addresses map to actual addresses?

The Internet is a collection of independent networks, each may contain many
computers

Each computer can then be identified by two things:
• The network where it belongs
• Its local address within this network

These two together define a 32-bit address for that machine

The address is often written as a sequence of four 8-bit numbers separated by
“.”

For example, concordia.ca is 132.205.7.63
8
I nternet Addressing


But now, which bits represent a network number and which
represent a local ID?
This depends on the type of address; IP recognizes several
classification of Internet addresses depending on the size of the
organization’s network
classification
byte1
byte2
byte3
byte4
# of NWs
max nodes
Class A
0nnnnnnn
xxxxxxxx
xxxxxxxx
xxxxxxxx
27
224
Class B
10nnnnnn
nnnnnnnn
xxxxxxxx
xxxxxxxx
214
216
Class C
110nnnnn
nnnnnnnn
nnnnnnnn
xxxxxxxx
221
28
(127)
(16,364)
(2,097,152)
Class D
multicast
1110 followed by a 28-bit multicast address
Class E
Reserved
1111; reserved
(>16 million)
(65,536)
(256)
n’s represent bits in the network number; x’s represent bits in the local identifier
9
I nternet Addressing

Example:
Which class does Concordia.ca belong (assume IP address:
132.205.7.63)? Which class does Nasa.gov belong (Assume
IP address: 64.37.246.3)?

Concordia.ca is 132.205.7.63, which is
10000100.11001101.00000111.00111111 which is class B

Nasa.gov has address: 64.37.246.3, which is
01000000.00100101.11110110.00000011
So it is class C
10
C lassless Addresses

The older version of IP, IPv4, has address depletion problem

Internet addresses are 32-bit, so there is only finite number of
addresses

232 ≈ 4.3 billion; isn’t that enough?

What if an organization has 1000 computers?

Two solutions exist:
• Use more bits for addresses (more than 32)
• Use Classless InterDomain Routing (CIDR)
11
CIDR

Specifies a group of addresses that do not fall into any
of the predefined classes

Each address in the group can still be interpreted as a
network number followed by a local identifier

Commonly used to allocate multiple class C addresses

For example, if a network has 1000 computers, CIDR
allocates 4 consecutive Class C addresses to that
network
12
CIDR

Example:
Class C
Bit representation
Address range
211.195.8.0
1101011-1100001100001000-xxxxxxxx
211.195.8.0 to
211.195.8.255
211.195.9.0
1101011-1100001100001001-xxxxxxxx
211.195.9.0 to
211.195.9.255
211.195.10.0
1101011-1100001100001010-xxxxxxxx
211.195.10.0 to
211.195.10.255
211.195.11.0
1101011-1100001100001011-xxxxxxxx
211.195.11.0 to
211.195.11.255
13
CIDR

Further, a router can extract the network number (in
this case it is 211.198.8.0), which is the 1st address of
this network

This can be done via logical AND operation between a
32-bit subnet mask (255.255.252.0) and an IP address
IP Address
1101011-11000011-000010xx-xxxxxxxx
AND with subnet mask
11111111-11111111-11111100-00000000
Network number
1101011-11000011-00001000-00000000
(which is, 211.195.8.0)
14
CIDR

In effect, CIDR groups several smaller networks together and
visualize them as a single large network; this is referred to as
supernetting

Advantages?

Yet, there is another issue: each IP packet has the destination IP
address, where the first 3 bits determine whether this is class A,
B or C

The rest of the bits in the address are then extracted to determine
the network number
15
CIDR

Determining the network number is straight forward when that
number of bits is fixed

With CIDR, this is not the case

The router must know the number of network bits

To allow that, the usual representation of an address (w.x.y.z) is
replaced by (w.x.y.z/m), where m is the number of bits in the
network ID

For the previous example, that will be: 211.195.8.0/22, which
means that the network number has 22 bits long
16
O btaining an Address

A computer connected to a company network, or
connected to an ISP, will get an IP address assigned

The machine may have a static IP address, or it may
dynamically require an IP address from the server

The server runs a protocol called Dynamic Host
Configuration Protocol (DHCP), which allocates the
machine one of the available IP addresses it maintains

Try ipconfig command
17
O btaining an Address

Prior to 1999, all network addresses were managed by
IANA, Internet Assigned Numbers Authority

In 1999, the Internet Corporation for Assigned Names
and Numbers (ICANN) assumed that responsibility
and others related to Domain Name System (DNS)

After all, isn’t IP addresses are hard to memorize?!
18
DNS

Use textual addresses instead of IP addresses to access a
network

DNS is a distributed database that enables the maping between
the textual and IP names

Why DNS is not centralized?

DNS is distributed among a collection of DNS servers, which
are scattered around the Internet

Try nslookup command in Unix
19
DNS

To facilitate the lookup process, servers are organized
into zones

A request for an textual name escalates, may go down,
until the IP address is found (or the process fails)
Figure 11.3 – DNS Hierarchy
20
DNS

Example
• What happens if try to access pc1.products.acme.com, where pc1 is an
existing machine

Once an IP address of a textual address is found, the involved servers in the
lookup process will keep this information in their cache so a next request is
processed faster
Figure 11.4 – Zones in
DNS Hierarchy
21
IP Routing

Based on routing tables

There is a distinction between physical addresses and IP
addresses

For example, an e-mail to
user@host.department.university.domain is translated into 32bit dotted IP address

The IP address is the unique address of the computer

The physical address is the one used by the underlying network
22
IP Routing

For example, a device connected to an Ethernet would
sense an Ethernet address on the segment to know
which packet is destined for it

However, this Ethernet address is a 48-bit address that
has no significance on a global IP scale

So, how can the device then recognize a packet
containing an IP address?
23
IP Routing

How the router determines the physical address from the IP
address when the packet is embedded into a LAN frame

When the router receives an IP packet, there are two
possibilities:
• The packet’s destination machine is in a network where the router is
attached, or
• It is not

If the destination machine belongs to the same network, then the
router can directly send the packet to the destination; that is
called Direct Routing

The router will know that since the network part of the IP
address is the same as its own network part
24
IP Routing

But still, how the router can determine the physical address from
the IP address?

One approach is the Dynamic Binding, also called Address
Resolution Protocol

The router transmits a broadcast request to all devices in the
LAN, specifying the IP address

The device with the specified IP responds with its physical
address

The router can then sends the packet to the proper device; it also
stores this information on a local cache for future requests
25
IP Routing

What if the destination is not directly reachable
through one of the router’s networks?

The router then uses hierarchical routing, as discussed
in previous lectures, to determine another router to
send the packet to

The packet will then travel from one router to another
until it reaches a router connected through the same
network to the destination machine
26
IP Routing

Example
Figure 11.7 –
IP Routing

Try traceroute command in Unix, or tracert on
Windows
27
R outers
Figure 11.8 – Router Function
28
R outers

Address lookup must occur very quickly. Why?

Any search method can be used, but some of them are too slow for many
routers to function fast enough

Content Addressable Memory, a hash structure, is probably the fastest

Instead of searching, use a hash function to calculate the next hop from the
destination
Figure 11.9 – HASH
Function to Update
Routing Tables
29
R outers

Moving the packet from the input port to the output port can
utilize the bus transport system approach, however this could be
too slow. Why?

Another approach is to use shared memory; where multiple
processors are capable of accessing at the same time

Once the next hop is known, the input port processor places the
packet on the queue (just a part of that shared memory) of the
output port
30
R outers

Another approach is to create a hardware switch that connects
each input port with each of the output ports
Figure 11.10 – Switch-based Router
31
R outers

What if many input port need to send to a single output port?

Scheduling is needed; first-in-first-out is simple but it may not
guarantee the required QoS

For example, compare file transfer application to a video
streaming one; the expected QoS is not the same

A priority queue may be used instead of a simple FIFO queue
32
M ulticast Routing

One multicast address, class D address, defines a set of
destination in contrast to a single one
Figure 11.11 – Multicasting Video
33
M ulticast Routing

The Internet Group Management Protocol (IGMP) is used to
enable a host to join or leave the multicast group

Multicast information must be delivered to all routers in the
network

Routers must implement some type of multicasting routing
algorithms

Not all routers in the network may need to be involved in a
multicast communication
34
M ulticast Routing

Which routers in the network need to be involved in a multicast
communication involving all the shown machines?
Figure 11.12 – Routers Involved in Multicasting
35
M ulticast Routing


What routers need to do when they receive a multicast packet?
If a minimal tree is created that connects all hosts in the
communication, then the answer is simple!
Figure 11.13 – Possible Multicast Trees for the Network in Figure 11.12
36
M ulticast Routing

A multicast tree can be created to connect all involved hosts, or

A multicast tree can be created to connect each source in a group
to all the rest

Regardless of either one to choose, creation of multicast trees,
especially for a large number of involved nodes, is not that easy

That is why the majority of IP routers do NOT support
multicasting

Those routers that support multicasting make up the Mbone, a
network within the Internet that supports class D address routing
37
M ulticast Routing

Mbone utilizes the Distance Vector Multicast Routing Protocol
(DVMRP), which has several components

One such component is the Reverse-Path Broadcasting (RPB)

RPB allows the packets to be broadcast while eliminating the
potential loop problems that broadcasting might cause

RPB assumes that a router knows the next link along the shortest
path to a given node

When a packet is received at port, the source is looked at. If
packets from that source are expected at that port (from a
previous hop), then broadcast the packet to all other ports;
otherwise drop it
38
M ulticast Routing

The idea of RPB is to forward the packet away from
the direction of the source; doing that in all routers
eliminates loops
Figure 11.14 – Router Executing Reverse Broadcast Protocol
39
M ulticast Routing

RPB by itself would not work for multicasting since not all paths may have
hosts that belong to the multicast group

Another component in DVMRP is a pruning algorithm, which limits when a
router forwards a message, hence eliminating the improper branches

When a router receives a multicast packet but it has no hosts that listening to
that address, it send a prune message to the originating router in which the
packet came from

When the originating router receives the prune message, it stops multicasting
in that direction

If later the router needs to receive these multicast packets, it must send a a
Graft message to the originating router
40
M ulticast Routing
Figure 11.15 – Pruning
41
T ransport Protocols

Transport layer provides the “connection” the user
perceives; the connection is a logical connection

Transport layer provides that perception by acting as an
interface between the user and the network protocols

Transport protocols are either connection-oriented or
connectionless
42
T ransport Protocols

Some transport layer functions include:
• Connection management: defines the rules that allow two
users to start talking; handshaking may be performed to
setup the connection
• Flow Control
• Error detection: not all errors are detected at the lower
layers; different errors are possible
• Response to users’ request: for example, user may request
high throughput, low delays, reliable services, …etc.
43
T ransmission Control Protocol (TCP)

Connection-oriented protocol that provides user-to-user
byte stream service

It defines a logical connection between two sites and
then transmits a byte stream sequence between them

The byte stream is divided into a sequence of segments
that is then sent using a variation of a sliding window
flow control protocol

Initial connection is initiated via handshaking
44
T ransmission Control Protocol (TCP)

TCP is reliable; even if the network below it is
unreliable
Figure 11.25 – TCP as a User-to-User Service
45
TCP’s Connection Management

Connection management is the process of establishing,
maintaining and disconnecting connections

A connection here is more virtual than physical

First establish the connection, then exchange the
needed parameters for the connection such as sequence
numbers used, the number of bytes an entity can
receive, ..etc.
46
TCP’s Connection Management

Establishing a connection may seem easy; one end
request a connection, the other end accepts; that is twoway handshaking
Figure 11.27 –
Failure of 2-way
Handshake Protocol
47
TCP’s Connection Management

TCP divides the message (stream of bytes) into
segments
Figure 11.26 – TCP Segment
48
TCP’s Connection Management

TCP uses three-way handshaking instead
Figure 11.28 – 3-way Handshake Protocol
49
TCP’s Connection Management

TCP provides full-duplex communication; so one
entity waiting to disconnect does not mean the other is
ready to disconnect

That is, the two parties must agree to disconnect

The protocol again uses three-way handshaking to
disconnect
50
TCP’s Connection Management
Figure 11.29 – TCP Disconnect Protocol
51
TCP’s Flow Control

TCP entities buffer sent segments since there is no
guarantee that they will correctly be received

The received segments are also buffered since there is
no guarantee that they arrive in sequence

Effectively, the entities use a variation of the sliding
window protocol with the following differences:
• In TCP flow control, the sequence number refers to byte
sequences instead of packet (or segment) sequence
• Either entity can dynamically alter the size of the other’s
sending window
52
TCP’s Flow Control

Each entity implements flow control using a credit mechanism,
also called a window advertisement

A credit specifies the maximum number of bytes that the entity
can receive and buffer from the other entity

The credit is in addition to those that have already been received
and buffered, but not yet delivered

Upon receiving this information, the entity can determine how
many bytes it can still send before it must wait for Acks.
53
TCP’s Flow Control
Figure 11.30 – Flow Control Using a Credit Mechanism
54
User Datagram Protocol (UDP)

Connectionless transport layer protocol

Does not guarantee reliable delivery of data

No handshake to establish/terminate connections

Just construct what to be send and give it to IP for delivery

If received data is okay, deliver it; otherwise discard it

No formal mechanism for acknowledging errors or for flow
control
Why then use UDP?

55