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Chapter 11
Distance-Vector Routing Protocols – RIP and IGRP
- IP routing is the process of transmitting packets from a network to another network. The main
concern of routers is networks instead of hosts. A router can only forward packets to routes
(or subnets) in its routing table. Routers are also known as gateways. A host would send packets
destined to another network to its default gateway of the local network.
- Routing protocols are used by routers to figure out the network topology, find paths to all the
networks in an internetwork, determine the best path to a network, and fill the routing tables with
the routing information. Ex: RIP, IGRP, OSPF, and EIGRP.
Routed protocols are used to define and assign logical addressing on physical interfaces,
encapsulate data into packets, and liaise with the data link layer to deliver packets through an
internetwork. These protocols allow packets to be forwarded by routing protocols. Ex: IP, IPX,
and AppleTalk. Note: IBM SNA, NetBIOS, and NetBEUI are non-routable protocols.
- A router always has the routes to directly connected networks. For non-directly connected
networks, the router must learn and know how to get to there. The information can be manually
configured (static routing), or learn from other routers using routing protocols (dynamic routing).
- Below list the 2 types of routing protocols:
Interior Gateway Protocols Used for exchanging routing information between routers
within an autonomous system (AS) (Intra-AS or intradomain).
Ex: RIP, IGRP, OSPF, and EIGRP.
Exterior Gateway Protocols Used for communication between autonomous systems
(Inter-AS or interdomain). Out of the scope of CCNA.
Ex: BGP.
- Autonomous system (AS) is a collection of networks that is within the administration control of
a company or organization that shares a common routing strategy.
- Static routing is the most basic way to tell a router where to forward packets to non-directly
connected networks. Static routes are manually added to and removed from a router’s routing
table; hence it is very tedious and impractical to implement static routing in large networks.
- Below list the 3 classes of dynamic routing protocols:
Distance-Vector Simple routing algorithm. Less effective and efficient compared to other
classes of routing protocols. Targeted for small networks. Ex: RIP, IGRP.
Link-State Complex routing algorithm. Frequently used in large and complex
networks. Ex: OSPF.
Balanced Hybrid Consists of both DV and LS concepts and features. Ex: EIGRP.
- Every routing protocol has its pros and cons. Good understanding of them is required to choose
and implement the best solution for specific situation and requirement.
- With Distance-Vector routing protocols, every router in a network advertises all its known
routes (complete routing table) to its neighboring routers. Finally, each router would have a
complete routing table to all the subnets in the network by combining the received routing
updates with its own routing table entries. A router running a Distance-Vector routing protocol
does not know the topology of the entire network.
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com