ROUTING PROTOCOLS
RIP VERSUS OSPF
The distinction between RIP and OSPF lies in the fundamental differences between distance vector protocols and link state protocols. Using a distance vector protocol, each router creates a unique routing table from summarized information obtained from neighboring routers. Using a link state protocol, every router maintains an identical routing table created from information obtained from all routers in the autonomous system. Each router builds a shortest path tree, using itself as the root. The link state protocol ensures that updates sent to neighboring routers are acknowledged by the neighbors, verifying that all routers have a consistent network map.
The biggest advantage of using RIP is that it is relatively simple to understand and implement, and it has been the de facto routing standard for many years.
RIP has a number of limitations that can cause problems in large networks, including the following:
•A limit of 15 hops between the source and destination networks
•A large amount of bandwidth taken up by periodic broadcasts of the entire routing table
•Slow convergence
•Routing decisions based on hop count; no concept of link costs or delay
•Flat networks; no concept of areas or boundaries
OSPF offers many advantages over RIP, including the following:
•No limitation on hop count
•Route updates multicast only when changes occur
•Faster convergence
•Support for load balancing to multiple routers based on the actual cost of the link
•Support for hierarchical topologies where the network is divided into areas
The details of RIP and OSPF are explained later in this chapter.
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