BigIron RX Series Configuration Guide 66553-1001986-01Configuring RIP parameters 24Syntax: [no] ip rip learn-defaultConfiguring a RIP neighbor filterBy default, a device learns RIP routes from all its RIP neighbors. Neighbor filters allow you to specifythe neighbor routers from which the device can receive RIP routes. Neighbor filters apply globally toall ports.To configure a RIP neighbor filters, enter a command such as the following.BigIron RX(config-rip-router)# neighbor 1 deny anySyntax: [no] neighbor permit | deny | anyThis command configures the device so that the device does not learn any RIP routes from any RIPneighbors.The following commands configure the device to learn routes from all neighbors except192.168.1.170. Once you define a RIP neighbor filter, the default action changes from learning allroutes from all neighbors to denying all routes from all neighbors except the ones you explicitlypermit. Thus, to deny learning from a specific neighbor but allow all other neighbors, you must adda filter that allows learning from all neighbors. Make sure you add the filter to permit all neighborsas the last filter (the one with the highest filter number). Otherwise, the software can match on thepermit all filter before a filter that denies a specific neighbor, and learn routes from that neighbor.BigIron RX(config-rip-router)# neighbor 2 deny 192.16.1.170BigIron RX(config-rip-router)# neighbor 1024 permit anyChanging the route loop prevention methodRIP uses the following methods to prevent routing loops:• Split horizon – The device does not advertise a route on the same interface as the one onwhich the router learned the route.• Poison reverse – The device assigns a cost of 16 (“infinite” or “unreachable”) to a route beforeadvertising it on the same interface as the one on which the router learned the route. This isthe default.These loop prevention methods are configurable on a global basis as well as on an individualinterface basis. One of the methods is always in effect on an interface enabled for RIP. Thus, if youdisable one method, the other method is enabled.NOTEThese methods are in addition to RIP’s maximum valid route cost of 15.To disable poison reverse and enable split horizon on a global basis, enter the following command.BigIron RX(config-rip-router)# no poison-reverseSyntax: [no] poison-reverseTo disable poison reverse and enable split horizon on an interface, enter commands such as thefollowing.BigIron RX(config-if-e10000-1/1)# no ip rip poison-reverseSyntax: [no] ip rip poison-reverse
