Compatible Systems 5.4 manual RIP Split Horizon, Output RIP Input RIP

24 Chapter 2 - IP Routing & Bridging

•If None is selected with this pull-down menu, the router will not be able to update its routing table and will always direct traffic for addresses it does not have a route for (addresses not on one of the networks connected to its interfaces) to the “gateway/port” defined in its IP Static Route Dialog Box. It will then be the responsibility of the default router to direct the packets to the correct address. For information on setting the default router see the discussion of the IP Static Route Dialog Box later in this chapter.

ϖNote: Some routers, in particular those designed to create very large corporate backbones, may use other routing protocols such as OSPF (Open Shortest Path First). These routers can simultaneously use RIP 1 (and in some cases RIP 2) to communicate with smaller routers, or each of the smaller routers can be set to use one of these backbone routers as their default router.

RIP Split Horizon

Normally, RIP uses a technique called split horizon to avoid routing loops and allow smaller update packets. This technique specifies that when the router sends a RIP update out a particular network interface, it should never include routing information acquired over that same interface.

There is a variation of the split horizon technique called “poison reverse” which specifies that all routes should be included in an update out a particular interface, but that the metric should be set to infinity for those routes acquired over that interface. One drawback is that routing update packet sizes will be increased when using poison reverse.

•If Split Horizon is selected with this pull-down menu, the router will apply the split horizon technique to routes being output over this inter- face.

•If No Split Horizon is selected with this pull-down menu, the router will include all routes in an output packet, regardless of which interface they were acquired over, and will use a normal metric.

•If Poison Reverse is selected with this pull-down menu, the router will include all routes in an output packet, but will set the metric to infinity for those routes which were acquired over this interface.

Output RIP - Input RIP

These flags control the behavior of RIP 1 and RIP 2 for this interface, allowing the router to selectively send RIP, receive RIP, or both. The default (assuming RIP 1 or RIP 2 is turned on in the Routing Protocol popup) is to both send and receive.