1 INTRA- AND INTERDOMAIN ROUTING Routing inside an autonomous system is referred to as intradomain routing. Routing between autonomous systems is referred

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INTRA- AND INTERDOMAIN ROUTING

Routing inside an autonomous system is referred to as intradomain Routing inside an autonomous system is referred to as intradomain routing. Routing between autonomous systems is referred to as routing. Routing between autonomous systems is referred to as interdomain routing. interdomain routing.

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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 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 the route with minimum distance. In this protocol each node maintains a vector (table) of minimum distances to every nodevector (table) of minimum distances to every node

The topics discussed in this section include:The topics discussed in this section include:

Initialization Initialization Sharing Sharing Updating Updating When to Share When to Share Two-Node Loop Instability Two-Node Loop Instability Three-Node Instability Three-Node Instability


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Distance vector routing tables


TCP/IP Protocol Suite 6

Figure 14.4 Initialization of tables in distance vector routing


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In distance vector routing, each node shares its routing table with its

immediate neighbors periodically and when there is a change.

Note:Note:


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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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RIP

The Routing Information Protocol (RIP) is an intradomain routing The Routing Information Protocol (RIP) is an intradomain routing protocol used inside an autonomous system. It is a very simple protocol protocol used inside an autonomous system. It is a very simple protocol based on distance vector routing. based on distance vector routing.


RIP Message Format RIP Message Format Requests and Responses Requests and Responses Timers in RIP Timers in RIP RIP Version 2 RIP Version 2 Encapsulation Encapsulation


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Example of a domain using RIP



Figure 14.9 RIP message format


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Figure 14.10 Request messages



Figure 14.13 RIP version 2 format



Figure 14.14 Authentication



RIP uses the services of UDP on well-known port 520.

Note:Note:


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LINK STATE ROUTING

In link state routing, if each node in the domain has the entire topology 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 of the domain, the node can use Dijkstra’s algorithm to build a routing table.table.


Building Routing Tables Building Routing Tables


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Concept of link state routing


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Figure 14.16 Link state knowledge

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Figure 14.17 Dijkstra algorithm


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Figure 14.18 Example of formation of shortest path tree

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Table 14.1 Table 14.1 Routing table for node ARouting table for node A


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14.5 OSPF

The Open Shortest Path First (OSPF) protocol is an intradomain The Open Shortest Path First (OSPF) protocol is an intradomain routing protocol based on link state routing. Its domain is also an routing protocol based on link state routing. Its domain is also an autonomous system. autonomous system.


Areas Areas Metric Metric Types of Links Types of Links Graphical Representation Graphical Representation OSPF Packets OSPF Packets Link State Update Packet Link State Update Packet Other Packets Other Packets Encapsulation Encapsulation


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Areas in an autonomous system


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Types of links



Figure 14.21 Point-to-point link


Figure 14.22 Transient link

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Figure 14.23 Stub link

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Figure 14.24 Example of an AS and its graphical representation in OSPF

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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

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Figure 14.28 LSA general header

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Figure 14.29 Router link


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Figure 14.30 Router link LSA

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Table 14.2 Table 14.2 Link types, link identification, and link dataLink types, link identification, and link data


OSPF packets are encapsulated in IP datagrams.

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14.7 BGP

Border Gateway Protocol (BGP) is an interdomain routing protocol Border Gateway Protocol (BGP) is an interdomain routing protocol using path vector routing. It first appeared in 1989 and has gone using path vector routing. It first appeared in 1989 and has gone through four versions. through four versions.

The topics discussed in this section include:The topics discussed in this section include:Types of Autonomous Systems Types of Autonomous Systems Path Attributes Path Attributes BGP Sessions BGP Sessions External and Internal BGP External and Internal BGP Types of Packets Types of Packets Packet Format Packet Format Encapsulation Encapsulation


Figure 14.50 Internal and external BGP sessions



Figure 14.51 Types of BGP messages


Figure 14.52 BGP packet header


Figure 14.53 Open message



Figure 14.54 Update message


BGP supports classless addressing and CIDR.

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Figure 14.55 Keepalive message



Figure 14.56 Notification message


Table 14.3 Table 14.3 Error codesError codes


BGP uses the services of TCP on port 179.

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Documents

1 INTRA- AND INTERDOMAIN ROUTING Routing inside an autonomous system is referred to as intradomain routing. Routing between autonomous systems is referred