INTRA- AND INTERDOMAIN ROUTING

1

INTRA
-

AND INTERDOMAIN


ROUTING

Routing

inside

an

autonomous

system

is

referred

to

as

intradomain

routing
.

Routing

between

autonomous

systems

is

referred

to

as

interdomain

routing
.


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2

Autonomous systems

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Figure 14.2

Popular routing protocols

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14.2 DISTANCE VECTOR ROUTING

In

distance

vector

routing,

the

least

cost

route

between

any

two

nodes

is

the

route

with

minimum

distance
.

In

this

protocol

each

node

maintains

a

vector

(table)

of

minimum

distances

to

every

node

The topics discussed in this section include:

Initialization

Sharing

Updating

When to Share

Two
-
Node Loop Instability

Three
-
Node Instability

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5

Distance vector routing tables

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TCP/IP Protocol Suite

6

Figure 14.4

Initialization of tables in distance vector routing

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7

In distance vector routing, each node
shares its routing table with its
immediate neighbors periodically and
when there is a change.

Note:

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8

Figure 14.5

Updating in distance vector routing

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Figure 14.6

Two
-
node instability

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Three
-
node instability

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11

RIP

The

Routing

Information

Protocol

(RIP)

is

an

intradomain

routing

protocol

used

inside

an

autonomous

system
.

It

is

a

very

simple

protocol

based

on

distance

vector

routing
.


The topics discussed in this section include:

RIP Message Format

Requests and Responses

Timers in RIP

RIP Version 2

Encapsulation

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12

Example of a domain using RIP

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TCP/IP Protocol Suite

13

Figure 14.9

RIP message format

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Figure 14.10

Request messages

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TCP/IP Protocol Suite

15

Figure 14.13

RIP version 2 format

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TCP/IP Protocol Suite

16

Figure 14.14

Authentication

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TCP/IP Protocol Suite

17

RIP uses the services of UDP on

well
-
known port 520.

Note:

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18


LINK STATE ROUTING

In

link

state

routing,

if

each

node

in

the

domain

has

the

entire

topology

of

the

domain,

the

node

can

use

Dijkstra’s

algorithm

to

build

a

routing

table
.

The topics discussed in this section include:

Building Routing Tables

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Concept of link state routing

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Figure 14.16

Link state knowledge

21

Figure 14.17

Dijkstra algorithm

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Figure 14.18

Example of formation of shortest path tree

23

Table 14.1
Routing table for node A

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14.5 OSPF

The

Open

Shortest

Path

First

(OSPF)

protocol

is

an

intradomain

routing

protocol

based

on

link

state

routing
.

Its

domain

is

also

an

autonomous

system
.


The topics discussed in this section include:

Areas

Metric

Types of Links

Graphical Representation

OSPF Packets

Link State Update Packet

Other Packets

Encapsulation

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Areas in an autonomous system

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Types of links

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TCP/IP Protocol Suite

27

Figure 14.21

Point
-
to
-
point link

TCP/IP Protocol Suite

28

Figure 14.22

Transient link

29

Figure 14.23

Stub link

30

Figure 14.24

Example of an AS and its graphical representation in OSPF

31

Figure 14.25

Types of OSPF packets

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Figure 14.26

OSPF common header

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Figure 14.27

Link state update packet

34

Figure 14.28

LSA general header

35

Figure 14.29

Router link

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Figure 14.30

Router link LSA

37

Table 14.2
Link types, link identification, and link data

TCP/IP Protocol Suite

38

OSPF packets are encapsulated in IP
datagrams.

Note:

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TCP/IP Protocol Suite

39

14.7 BGP

Border

Gateway

Protocol

(BGP)

is

an

interdomain

routing

protocol

using

path

vector

routing
.

It

first

appeared

in

1989

and

has

gone

through

four

versions
.


The topics discussed in this section include:

Types of Autonomous Systems

Path Attributes

BGP Sessions

External and Internal BGP

Types of Packets

Packet Format

Encapsulation

TCP/IP Protocol Suite

40

Figure 14.50

Internal and external BGP sessions

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TCP/IP Protocol Suite

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Figure 14.51

Types of BGP messages

TCP/IP Protocol Suite

42

Figure 14.52

BGP packet header

TCP/IP Protocol Suite

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Figure 14.53

Open message

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TCP/IP Protocol Suite

44

Figure 14.54

Update message

TCP/IP Protocol Suite

45

BGP supports classless addressing and
CIDR.

Note:

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TCP/IP Protocol Suite

46

Figure 14.55

Keepalive message

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TCP/IP Protocol Suite

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Figure 14.56

Notification message

TCP/IP Protocol Suite

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Table 14.3
Error codes

TCP/IP Protocol Suite

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BGP uses the services of TCP

on port 179.

Note:

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