Split-horizon

Non-broadcast networks (such as F/R), you may want to disable split horizon with RIP.

If an interface is configured with secondary IP addresses and split horizon is enabled, updates might not be sourced by the secondary address. One routing update is sourced per network number unless split horizon is disabled.

Split horizon for F/R (and SMDS) encapsulation is disabled by default. For all other encapsulations, split horizon is enabled by default.

If split horizon is disabled on a serial interface (and that interface is attached to a packet-switched network), you must disable split horizon for all routers in any relevant multicast groups on that network.

Default route (default network)

Cisco IOS software will source the default network with RIP if one of the following conditions is met:

• The ip default-network command is configured.
• The default-information originate command is configured.
• The default route is learned via another routing protocol or static route and then redistributed into RIP.

Auto summary

Automatic summary will override the configured summary address feature on a given interface except when both of the following conditions are true:

• The configured interface summary address and the IP address of the configured interface share the same major network (the classful, nonsubnetted portion of the IP address).
• Split horizon is not enabled on the interface.

If split horizon is enabled, neither an automatic summary address nor the interface summary address is advertised.

Does RIP support triggered updates?

Router(config-if)# ip rip triggered (Enables triggered extensions to RIP for use on serial links)

Redistribution into RIP:

Because metrics for different protocols cannot be directly compared, you must specify the default metric in order to designate the cost of the redistributed route used in RIP updates. All routes that are redistributed will use the default metric unless the metric is specified on the redistribute command itself.

router rip
default-metric <0-16>
redistribute [<protocol> <process-id>]

or

router rip
redistribute [<protocol> <process-id>] metric <0-16>

Verifying advertised and received routes

Debug ip rip is the only option to verify advertised and received routes. Unlike BGP RIP has no separate database(s) for advertised or received routes so there is no show command at hand.

debug ip rip events = shows updates being sent to mcast or unicast address, via which interface, with what source address and how many routes are in the update.

debug ip rip database = shows received updates being accepted or rejected, if accepted it displays the route(s) and its parameters being added to the database.

debug ip rip = shows advertised and received routes:

C3560(config-router)#
1w1d: RIP: sending v2 update to 224.0.0.9 via Vlan73 (20.1.1.5)
1w1d: RIP: build update entries
1w1d: 15.1.0.0/16 via 0.0.0.0, metric 1, tag 0
1w1d: 15.2.0.0/16 via 0.0.0.0, metric 1, tag 0
1w1d: RIP: received v2 update from 20.1.1.4 on Vlan45
1w1d: 3.0.0.0/8 via 0.0.0.0 in 1 hops