Configuring RIP
This chapter describes how to configure the ASA to route data, perform authentication, and redistribute routing information, using the Routing Information Protocol (RIP) routing protocol. This chapter includes the following sections:• Overview, page 22-1• Licensing Requirements for RIP, page 22-2• Guidelines and Limitations, page 22-2• Configuring RIP, page 22-3• Customizing RIP, page 22-3• Monitoring RIP, page 22-8• Configuration Example for RIP, page 22-9• Feature History for RIP, page 22-10• Additional References, page 22-10Overview
The Routing Information Protocol, or RIP, as it is more commonly called, is one of the most enduring
of all routing protocols. RIP has four basic components: routing update process, RIP routing metrics,
routing stability, and routing timers. Devices that support RIP send routing-update messages at regular
intervals and when the network topology changes. These RIP packets contain information about the
networks that the devices can reach, as well as the number of routers or gateways that a packet must
travel through to reach the destination address. RIP generates more traffic than OSPF, but is easier to
configure.
RIP has advantages over static routes because the initial configuration is simple, and you do not need to
update the configuration when the topology changes. The disadvantage to RIP is that there is more
network and processing overhead than static routing.
The ASA supports RIP Version 1 and RIP Version 2.
Routing Update Process
RIP sends routing-update messages at regular intervals and when the network topology changes. When
a router receives a routing update that includes changes to an entry, it updates its routing table to reflect
the new route. The metric value for the path is increased by 1, and the sender is indicated as the next hop
RIP routers maintain only the best route (the route with the lowest metric value) to a destination. After
updating its routing table, the router immediately begins transmitting routing updates to inform other
network routers of the change. These updates are sent independently of the regularly scheduled updates
that RIP routers send
RIP Routing Metric
RIP uses a single routing metric (hop count) to measure the distance between the source and a destination
network. Each hop in a path from source to destination is assigned a hop count value, which is typically
1. When a router receives a routing update that contains a new or changed destination network entry, the
router adds 1 to the metric value indicated in the update and enters the network in the routing table. The
IP address of the sender is used as the next hop.
RIP Stability Features
RIP prevents routing loops from continuing indefinitely by implementing a limit on the number of hops
allowed in a path from the source to a destination. The maximum number of hops in a path is 15. If a
router receives a routing update that contains a new or changed entry, and if increasing the metric value
by 1 causes the metric to be infinity (that is, 16), the network destination is considered unreachable. The
downside of this stability feature is that it limits the maximum diameter of a RIP network to less than 16
hops.
RIP includes a number of other stability features that are common to many routing protocols. These
features are designed to provide stability despite potentially rapid changes in network topology. For
example, RIP implements the split horizon and holddown mechanisms to prevent incorrect routing
information from being propagated.
RIP Timers
RIP uses numerous timers to regulate its performance. These include a routing-update timer, a
route-timeout timer, and a route-flush timer. The routing-update timer clocks the interval between
periodic routing updates. Generally, it is set to 30 seconds, with a small random amount of time added
whenever the timer is reset. This is done to help prevent congestion, which could result from all routers
simultaneously attempting to update their neighbors. Each routing table entry has a route-timeout timer
associated with it. When the route-timeout timer expires, the route is marked invalid but is retained in
the table until the route-flush timer expires.
Licensing Requirements for RIP
Model License Requirement
1.All models 1. Base License
Guidelines and Limitations
This section includes the guidelines and limitations for this feature:
1.Context Mode Guidelines
Supported in single and multiple context mode.
2.Firewall Mode Guidelines
Supported in routed and transparent firewall mode.
3.IPv6 Guidelines
Does not support IPv6.
Configuring RIP
This section explains how to enable and restart the RIP process on your system.
• Enabling RIP, page 22-3
After enabling see the section Customizing RIP, page 22-3, to learn how to customize the RIP process
on your system
Enabling RIP
You can only enable one RIP routing process on the ASA. After you enable the RIP routing process, you
must define the interfaces that will participate in that routing process using the network command. By
default, the ASA sends RIP Version 1 updates and accepts RIP Version 1 and Version 2 updates.
To enable the RIP routing process, perform the following step:
Detailed Steps
Command Purpose
router rip
Example:
hostname(config)# router rip
This starts the RIP routing process and places you
Use the no router rip command to remove entire RIP configuration you have enabled. Once this is
cleared, you must reconfigure RIP again using the router rip command.
Customizing RIP
This section describes how to configure RIP, and includes the following topics:
• Generating a Default Route, page 22-4
• Configuring Interfaces for RIP, page 22-4
• Disabling Route Summarization, page 22-5
• Filtering Networks in RIP, page 22-5
• Redistributing Routes into the RIP Routing Process, page 22-6
• Configuring RIP Send/Receive Version on an Interface, page 22-7
• Enabling RIP Authentication, page 22-8
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Configuring Interfaces for RIP
If you have an interface that you do not want to participate in RIP routing, but that is attached to a
network that you want advertised, you can configure a network command that covers the network to
which the interface is attached, and use the passive-interface command to prevent that interface from
sending RIP advertisements. Additionally, you can specify the version of RIP that is used by the ASA
for updates.
Disabling Route Summarization
RIP Version 1 always uses automatic route summarization. You cannot disable this feature for RIP
Version 1. RIP Version 2 uses automatic route summarization by default. The RIP routing process
summarizes on network number boundaries. This can cause routing problems if you have
non-contiguous networks.
For example, if you have a router with the networks 192.168.1.0, 192.168.2.0, and 192.168.3.0
connected to it, and those networks all participate in RIP, the RIP routing process creates the summary
address 192.168.0.0 for those routes. If an additional router is added to the network with the networks
192.168.10.0 and 192.168.11.0, and those networks participate in RIP, they will also be summarized as
192.168.0.0. To prevent the possibility of traffic being routed to the wrong location, you should disable
automatic route summarization on the routers creating the conflicting summary addresses.
To disable automatic router summarization, enter the following command in router configuration mode
for the RIP routing process:
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