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RIP is an older distance-vector routing protocol suitable for use in small, homogeneous networks.

Theory

Routing Information Protocol or RIP is the classic distance-vector routing protocol. It was documented in RFC 1058. The CCIE exams test on version 2 of this protocol. When enabled with default settings, RIP only sends v1 messages but listens to both v1 and v2 messages.

RIPv2 sends multicast updates (v1 used broadcast packets) on UDP port 520 to 224.0.0.9. Unlike more dynamic routing protocols such as OSPF or EIGRP, RIP forms no formal neighbor relationships and uses no hello packets. RIP sends all of it's routes with each update (full updates).

RIP uses hop count as it's routing metric. The hop count is the number of routers that can be transversed in a route, up to a maximum of 15. When advertising hop counts for routes to its peers, an RIP router will add 1 for each route. Connected routes have a hop count of 0, and a hop count of 16 indicates an unreachable route.

RIP utilizes a number of basic timers for its operation:

• Update - Cisco IOS RIP sends updates of it's routing information every 30 seconds out RIP-enabled interfaces.
• Invalid - Amount of time after which RIP will mark a route as invalid if no updates for it are heard. 180 seconds by default. When this expires, RIP will mark the route as infinite (hop count 16) and advertise it as unreachable; but the route will still be used to forward packets on.
• Flush - This timer starts after the invalid timer expires. When the flush timer expires for a route, the route will be removed from the routing table.
• Holddown - Cisco-proprietary timer. A 180 second timer that starts when a route's metric changes. RIP will not accept new sources of updates for this route until the timer expires.

The network command (always used in classful form) is used to advertise locally connected routes. When receiving a RIP update, a route must be in the routing table as a RIP route in order to be processed. If the route is listed as another protocol it will not be considered locally or passed along to other peers.

Commands

• router rip (global) - Enables the RIP protocol on the router and enters the CLI into router configuration mode.
• network ip-address (router) - Associates a network with the RIP process
• timers basic update invalid holddown flush [sleeptime] (router) - Command to adjust the default RIP timers. The sleeptime timer allows you to delay the RIP regular updates after receiving a triggered update.

Default Settings

• RIP will send messages in v1 format and listen to both v1 and v2 messages by default.
• 30 second update timer
• 180 second invalid timer
• 240 second flush timer
• 180 second holddown timer

Verification

• Nothing listed yet

Troubleshooting, Tips, and Tricks

• Nothing listed yet

Online Resources

• Cisco IOS IP routing configuration guide on configuring Routing Information Protocol.

• Cisco TAC training module on Routing Information Protocol (RIP) (must be registered to view).

• Wikipedia entry on the Routing Information Protocol.

• Caue of Cisco Network Engineer goes over the basics of RIP.

• Three ways to pass RIP routes between spokes from Tassos of CCIE in 3 Months.

• Some general RIPv2 notes from CCIE Talk.

• Cisco has a technote on the RIP delayed start feature.

• Sesano lists out the RIPv2 basics.

• Ivan of Cisco IOS Hints and Tricks shows us that RIP multicast updates are sent with a TTL of 2. Unicast updates, on the other hand, are sent with a TTL of 225.

• RIPv2 - Things to remember from Cisco Bible!.

• Configuring RIP from [http://synjunkie.blogspot.com

Synjunkie].

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