Extreme Networks 200 Series Routing Table, Split Horizon, Pois on Revers e, Tr i g ge re d U pd a t es, Route Advertisement of VLANs, RI P Ve rs ion 1 Ve rs us RI P Ve rs ion 2

Overview of RIP

Summit 200 Series Switch Installation and User Guide 209

Routing Table

The routing table in a router using RIP contains an entry for every known destination network. Each

routing table entry contains the following information:

•IP address of the destination network

•Metric (hop count) to the destination network

•IP address of the next router

•Timer that tracks the amount of time since the entry was last updated

The router exchanges an update message with each neighbor every 30 seconds (default value), or if

there is a change to the overall routed topology (also called triggered updates). If a ro ut er do e s n ot rec ei ve

an update message from its neighbor within the route timeout period (180 seconds by default), the

router assumes the connection between it and its neighbor is no longer available.

Split horizon is a scheme for avoiding problems caused by including routes in updates sent to the

router from which the route was learned. Split horizon omits routes learned from a neighbor in updates

sent to that neighbor.

Like split horizon, poison reverse is a scheme for eliminating the possibility of loops in the routed

topology. In this case, a router advertises a route over the same interface that supplied the route, but the

route uses a hop count of 16, defining it as unreachable.

Triggered updates occur whenever a router changes the metric for a route, and it is required to send an

update message immediately, even if it is not yet time for a regular update message to be sent. This will

generally result in faster convergence, but may als o result i n more R IP-relat ed traffi c.

VLANs that are configured with an IP address, but are configured to not route IP or are not configured

to run RIP, do not have their subnets advertised by RIP. Only those VLANs that are configured with an

IP address and are configured to route IP and run RIP have their subnets advertised.

A new version of RIP, called RIP version 2, expands the functionality of RIP version 1 to include:

•Variable-Length Subnet Masks (VLSMs).

•Support for next-hop addresses, which allows for optimization of routes in certain environments.

•Multicasting.

RIP version 2 packets can be multicast instead of being broadcast, reducing the load on hosts that do

not support routing protocols.