The Routing Information Protocol (RIP) is a classic distance vector Interior Gateway Protocol (IGP) designed to exchange information within an autonomous system (AS) of a small network.
This module describes the concepts and tasks to implement basic RIP routing. Cisco IOS XR software supports a standard implementation of RIP Version 2 (RIPv2) that supports backward compatibility with RIP Version 1 (RIPv1) as specified by RFC 2453.
For RIP configuration information related to the following features, see the Related Documents section of this module.
For more information about RIP on the Cisco IOS XR software and complete descriptions of the RIP commands listed in this module, see the Related Documents section of this module. To locate documentation for other commands that might appear while performing a configuration task, search online in the Cisco IOS XR Commands Master List for the Cisco CRS Router.
Feature History for Implementing RIP
This feature was introduced.
Four-byte autonomous system (AS) number support was added.
You must be in a user group associated with a task group that includes the proper task IDs. The command reference guides include the task IDs required for each command. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance.
RIP Version 1 (RIP v1) is a classful, distance-vector protocol that is considered the easiest routing protocol to implement. Unlike OSPF, RIP broadcasts User Datagram Protocol (UDP) data packets to exchange routing information in internetworks that are flat rather than hierarchical. Network complexity and network management time is reduced. However, as a classful routing protocol, RIP v1 allows only contiguous blocks of hosts, subnets or networks to be represented by a single route, severely limiting its usefulness.
RIP v2 allows more information carried in RIP update packets, such as support for:
Classless interdomain routing (CIDR)
Variable-length subnet masks (VLSMs)
Autonomous systems and the use of redistribution
Multicast address 22.214.171.124 for RIP advertisements
The metric that RIP uses to rate the value of different routes is hop count. The hop count is the number of routers that can be traversed in a route. A directly connected network has a metric of zero; an unreachable network has a metric of 16. This small range of metrics makes RIP an unsuitable routing protocol for large networks.
Routing information updates are advertised every 30 seconds by default, and new updates discovered from neighbor routers are stored in a routing table.
Only RIP Version 2 (RIP v2), as specified in RFC 2453, is supported on Cisco IOS XR software and, by default, the software only sends and receives RIP v2 packets. However, you can configure the software to send, or receive, or both, only Version 1 packets or only Version 2 packets or both version type packets per interface.
Here are some good reasons to use RIP:
Compatible with diverse network devices
Best for small networks, because there is very little overhead, in terms of bandwidth used, configuration, and management time
Support for legacy host systems
Because of RIP’s ease of use, it is implemented in networks worldwide.
Split Horizon for RIP
Normally, routers that are connected to broadcast-type IP networks and that use distance-vector routing protocols employ the split horizon mechanism to reduce the possibility of routing loops. Split horizon blocks information about routes from being advertised by a router out of any interface from which that information originated. This behavior usually optimizes communications among multiple routers, particularly when links are broken.
If an interface is configured with secondary IP addresses and split horizon is enabled, updates might not be sourced by every secondary address. One routing update is sourced per network number unless split horizon is disabled.
The split horizon feature is enabled by default. In general, we recommend that you do not change the default state of split horizon unless you are certain that your operation requires the change in order to properly advertise routes.
Route Timers for RIP
RIP uses several timers that determine such variables as the frequency of routing updates, the length of time before a route becomes invalid, and other parameters. You can adjust these timers to tune routing protocol performance to better suit your internetwork needs, by making the following timer adjustments to:
The rate (time in seconds between updates) at which routing updates are sent
The interval of time (in seconds) after which a route is declared invalid
The interval (in seconds) during which routing information regarding better paths is suppressed
The amount of time (in seconds) that must pass before a route is removed from the RIP topology table
The amount of time delay between RIP update packets
The first four timer adjustments are configurable by the timers basic command. The output-delay command changes the amount of time delay between RIP update packets. See Customizing RIP for configuration details.
It also is possible to tune the IP routing support in the software to enable faster convergence of the various IP routing algorithms and quickly drop back to redundant routers, if necessary. The total result is to minimize disruptions to end users of the network in situations in which quick recovery is essential.
Route Redistribution for RIP
Redistribution is a feature that allows different routing domains, to exchange routing information. Networking devices that route between different routing domains are called boundary routers, and it is these devices that inject the routes from one routing protocol into another. Routers within a routing domain only have knowledge of routes internal to the domain unless route redistribution is implemented on the boundary routers.
When running RIP in your routing domain, you might find it necessary to use multiple routing protocols within your internetwork and redistribute routes between them. Some common reasons are:
To advertise routes from other protocols into RIP, such as static, connected, OSPF, and BGP.
To migrate from RIP to a new Interior Gateway Protocol (IGP) such as EIGRP.
To retain routing protocol on some routers to support host systems, but upgrade routers for other department groups.
To communicate among a mixed-router vendor environment. Basically, you might use a protocol specific to Cisco in one portion of your network and use RIP to communicate with devices other than Cisco devices.
Further, route redistribution gives a company the ability to run different routing protocols in work groups or areas in which each is particularly effective. By not restricting customers to using only a single routing protocol, Cisco IOS XR route redistribution is a powerful feature that minimizes cost, while maximizing technical advantage through diversity.
When it comes to implementing route redistribution in your internetwork, it can be very simple or very complex. An example of a simple one-way redistribution is to log into a router on which RIP is enabled and use the redistribute static command to advertise only the static connections to the backbone network to pass through the RIP network. For complex cases in which you must consider routing loops, incompatible routing information, and inconsistent convergence time, you must determine why these problems occur by examining how Cisco routers select the best path when more than one routing protocol is running administrative cost.
Default Administrative Distances for RIP
Administrative distance is used as a measure of the trustworthiness of the source of the IP routing information. When a dynamic routing protocol such as RIP is configured, and you want to use the redistribution feature to exchange routing information, it is important to know the default administrative distances for other route sources so that you can set the appropriate distance weight.
This table lists the Default Administrative Distances of Routing Protocols.
Table 1 Default Administrative Distances of Routing Protocols
Administrative Distance Value
Static route out an interface
Static route to next hop
EIGRP Summary Route
RIP version 1 and 2
An administrative distance is an integer from 0 to 255. In general, the higher the value, the lower the trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored. Administrative distance values are subjective; there is no quantitative method for choosing them.
Routing Policy Options for RIP
Route policies comprise series of statements and expressions that are bracketed with the route-policy and end-policy keywords. Rather than a collection of individual commands (one for each line), the statements within a route policy have context relative to each other. Thus, instead of each line being an individual command, each policy or set is an independent configuration object that can be used, entered, and manipulated as a unit.
Each line of a policy configuration is a logical subunit. At least one new line must follow the then, else, and end-policy keywords. A new line must also follow the closing parenthesis of a parameter list and the name string in a reference to an AS path set, community set, extended community set, or prefix set. At least one new line must precede the definition of a route policy, AS path set, community set, extended community set, or prefix set. One or more new lines can follow an action statement. One or more new lines can follow a comma separator in a named AS path set, community set, extended community set, or prefix set. A new line must appear at the end of a logical unit of policy expression and may not appear anywhere else.
How to Implement RIP
This section contains instructions for the following tasks:
To save configuration changes, you must commit changes when the system prompts you.
(Optional) Configures RIP to send only Version 2 packets to the broadcast IP address rather than the RIP v2 multicast address (126.96.36.199). This command can be applied at the interface or global configuration level.
In general, we do not recommend changing the state of the default for the split-horizon command, unless you are certain that your application requires a change to properly advertise routes. 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 networking devices in any relevant multicast groups on that network.
Adjusting RIP Timers for each VRF Instance: Example
The following example shows how to adjust RIP timers for each VPN routing and forwarding (VRF) instance.
For VRF instance vpn0, the timers basic command sets updates to be broadcast every 10 seconds. If a router is not heard from in 30 seconds, the route is declared unusable. Further information is suppressed for an additional 30 seconds. At the end of the flush period (45 seconds), the route is flushed from the routing table.
For VRF instance vpn1, timers are adjusted differently: 20, 60, 60, and 70 seconds.
The output-delay command changes the interpacket delay for RIP updates to 10 milliseconds on vpn1. The default is that interpacket delay is turned off.
The following example shows how to redistribute Border Gateway Protocol (BGP) and static routes into RIP.
The RIP metric used for redistributed routes is determined by the route policy. If a route policy is not configured or the route policy does not set RIP metric, the metric is determined based on the redistributed protocol. For VPNv4 routes redistributed by BGP, the RIP metric set at the remote PE router is used, if valid.
In all other cases (BGP, IS-IS, OSPF, EIGRP, connected, static), the metric set by the default-metric command is used. If a valid metric cannot be determined, then redistribution does not happen.
The following example shows how to configure inbound and outbound route policies that are used to control which route updates are received by a RIP interface or sent out from a RIP interface.
if destination in pf1 then
if destination in pf2 then
add rip-metric 2
route-policy policy_in in
route-policy infil in
route-policy pass-all out
Configuring Passive Interfaces and Explicit Neighbors for RIP: Example
The following example shows how to configure passive interfaces and explicit neighbors. When an interface is passive, it only accepts routing updates. In other words, no updates are sent out of an interface except to neighbors configured explicitly.
The following example shows how to use the distance command to install RIP routes in the Routing Information Base (RIB). The maximum-paths command controls the number of maximum paths allowed per RIP route.
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