Scalability Features of Routing Protocols

Scalability Features of Routing Protocols
Several times in this book as we look at the different routing protocols—IS-IS, OSPF, IGRP,
EIGRP, and BGP—we will refer back to distance-vector and link-state routing protocol differences.
It is important to understand how these protocols differ from one another.
As networks grow and administrators implement or use Cisco-powered networks, IS-IS and
OSPF might not be the most efficient or recommended protocols to use. IS-IS and OSPF do have
some advantages over IGRP and EIGRP, including the following:

They are versatile.

They use a very scalable routing algorithm.

They allow the use of a routing protocol that is compatible with non-Cisco routers.
Cisco provides two proprietary solutions that allow better scaling and convergence, which can
be very critical issues. These are the Interior Gateway Routing Protocol (IGRP) and Enhanced
IGRP (EIGRP), with EIGRP offering, by far, the better scaling and convergence of the two. Network
growth imposes a great number of changes on the network environment and takes into consideration
the following factors:

The number of hops between end systems

The number of routes in the routing table
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The different ways a route was learned

Route convergence
IGRP and EIGRP can be used to maintain a very stable routing environment, which is absolutely
crucial in larger networks.
As the effects of network growth start to manifest themselves, whether your network’s routers
can meet the challenges faced in a larger scaled network is completely up to the routing protocol
the routers are running. If you use a protocol that’s limited by the number of hops it can
traverse, the number of routes it can store in its table, or even the inability to communicate with
other protocols, then you have a protocol that will likely hinder the growth of your network.
All the issues we’ve discussed so far are general scalability considerations. Before we look at
IGRP and EIGRP, let’s take another look at the differences between link-state routing protocols
and distance-vector protocols and the scalability issues of each.
Link-state routing and distance-vector protocols are discussed in detail in
Chapter 1, ”Routing Principles.“