RIP uses broadcast User Datagram Protocol (UDP) data packets to exchange routing information.
The Cisco IOS software sends routing information updates every 30 seconds; this process is termed
advertising. If a router does not receive an update from another router for 180 seconds or more, it
marks the routes served by the nonupdating router as being unusable. If there is still no update after
240 seconds, the router removes all routing table entries for the nonupdating router.
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.
If the router has a default network path, RIP advertises a route that links the router to the
pseudonetwork 0.0.0.0. The network 0.0.0.0 does not exist; RIP treats 0.0.0.0 as a network to
implement the default routing feature. The Cisco IOS software will advertise the default network if
a default was learned by RIP, or if the router has a gateway of last resort and RIP is configured with
a default metric.
RIP sends updates to the interfaces in the specified networks. If an interface’s network is not
specified, it will not be advertised in any RIP update.
Cisco’s implementation of RIP Version 2 supports plain text and MD5 authentication, route
summarization, classless interdomain routing (CIDR), and variable-length subnet masks (VLSMs).
For protocol-independent features, which also apply to RIP, see the chapter “Configuring IP Routing
Protocol-Independent Features” in this document.
RIP Configuration Task List
To configure RIP, complete the tasks in the following sections. You must enable RIP. The remaining
tasks are optional.
• Enable RIP
• Allow Unicast Updates for RIP
Enable RIP
P1C-90 Network Protocols Configuration Guide, Part 1
• Apply Offsets to Routing Metrics
• Adjust Timers
• Specify a RIP Version
• Enable RIP Authentication
• Disable Route Summarization
• Run IGRP and RIP Concurrently
• Disable the Validation of Source IP Addresses
• Enable or Disable Split Horizon
• Configure Interpacket Delay
• Filtering RIP information
• Key management (available in RIP Version 2)
• VLSM
Enable RIP
To enable RIP, use the following commands, starting in global configuration mode:
Allow Unicast Updates for RIP
Because RIP is normally a broadcast protocol, in order for RIP routing updates to reach
nonbroadcast networks, you must configure the Cisco IOS software to permit this exchange of
routing information. To do so, use the following command in router configuration mode:
To control the set of interfaces with which you want to exchange routing updates, you can disable
the sending of routing updates on specified interfaces by configuring the passive-interface
command. See the discussion on filtering in the “Filter Routing Information” section in the
“Configuring IP Routing Protocol-Independent Features” chapter.
Apply Offsets to Routing Metrics
An offset list is the mechanism for increasing incoming and outgoing metrics to routes learned via
RIP. This is done to provide a local mechanism for increasing the value of routing metrics.
Optionally, you can limit the offset list with either an access list or an interface. To increase the value
of routing metrics, use the following command in router configuration mode:
router rip
version 1 or 2 ( 1 is default)
network X.X.X.X ( X=IP address)
no auto-summary
Adjust Timers
Routing protocols use 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. You can
make the following timer adjustments:
• 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 routing table
• The amount of time for which routing updates will be postponed
It also is possible to tune the IP routing support in the software to enable faster convergence of the
various IP routing algorithms, and, hence, quicker fallback to redundant routers. The total effect is
to minimize disruptions to end users of the network in situations where quick recovery is essential.
To adjust the timers, use the following command in router configuration mode:
Specify a RIP Version
Cisco’s implementation of RIP Version 2 supports authentication, key management, route
summarization, classless interdomain routing (CIDR), and variable-length subnet masks (VLSMs).
Key management and VLSM are described in the chapter “Configuring IP Routing
Protocol-Independent Features.”
By default, the software receives RIP Version 1 and Version 2 packets, but sends only Version 1
packets. You can configure the software to receive and send only Version 1 packets. Alternatively,
you can configure the software to receive and send only Version 2 packets. To do so, use the
following command in router configuration mode:
Command Purpose
offset-list [access-list-number | name] {in | out} offset
[type number]
Apply an offset to routing metrics.
Command Purpose
timers basic update invalid holddown flush [sleeptime] Adjust routing protocol timers.
Command Purpose
version {1 | 2} Configure the software to receive and send only
RIP Version 1 or only RIP Version 2 packets.
The preceding task controls the default behavior of RIP. You can override that behavior by
configuring a particular interface to behave differently. To control which RIP version an interface
sends, use one of the following commands in interface configuration mode:
Similarly, to control how packets received from an interface are processed, use one of the following
commands in interface configuration mode:
Enable or Disable Split Horizon
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. However, with nonbroadcast networks (such as
Frame Relay and SMDS), situations can arise for which this behavior is less than ideal. For these
situations, you might want to disable split horizon. This applies to IGRP and RIP.
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.
To enable or disable split horizon, use one of the following commands in interface configuration
mode:
Split horizon for Frame Relay and SMDS encapsulation is disabled by default. Split horizon is not
disabled by default for interfaces using any of the X.25 encapsulations. For all other encapsulations,
split horizon is enabled by default.
See the “Split Horizon Examples” section at the end of this chapter for examples of using split
horizon.
Note In general, changing the state of the default is not recommended unless you are certain that
your application requires making a change in order to advertise routes properly. Remember: 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.
ip split-horizon :Enable split horizon.
no ip split-horizon :Disable split horizon.
The Cisco IOS software sends routing information updates every 30 seconds; this process is termed
advertising. If a router does not receive an update from another router for 180 seconds or more, it
marks the routes served by the nonupdating router as being unusable. If there is still no update after
240 seconds, the router removes all routing table entries for the nonupdating router.
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.
If the router has a default network path, RIP advertises a route that links the router to the
pseudonetwork 0.0.0.0. The network 0.0.0.0 does not exist; RIP treats 0.0.0.0 as a network to
implement the default routing feature. The Cisco IOS software will advertise the default network if
a default was learned by RIP, or if the router has a gateway of last resort and RIP is configured with
a default metric.
RIP sends updates to the interfaces in the specified networks. If an interface’s network is not
specified, it will not be advertised in any RIP update.
Cisco’s implementation of RIP Version 2 supports plain text and MD5 authentication, route
summarization, classless interdomain routing (CIDR), and variable-length subnet masks (VLSMs).
For protocol-independent features, which also apply to RIP, see the chapter “Configuring IP Routing
Protocol-Independent Features” in this document.
RIP Configuration Task List
To configure RIP, complete the tasks in the following sections. You must enable RIP. The remaining
tasks are optional.
• Enable RIP
• Allow Unicast Updates for RIP
Enable RIP
P1C-90 Network Protocols Configuration Guide, Part 1
• Apply Offsets to Routing Metrics
• Adjust Timers
• Specify a RIP Version
• Enable RIP Authentication
• Disable Route Summarization
• Run IGRP and RIP Concurrently
• Disable the Validation of Source IP Addresses
• Enable or Disable Split Horizon
• Configure Interpacket Delay
• Filtering RIP information
• Key management (available in RIP Version 2)
• VLSM
Enable RIP
To enable RIP, use the following commands, starting in global configuration mode:
Allow Unicast Updates for RIP
Because RIP is normally a broadcast protocol, in order for RIP routing updates to reach
nonbroadcast networks, you must configure the Cisco IOS software to permit this exchange of
routing information. To do so, use the following command in router configuration mode:
To control the set of interfaces with which you want to exchange routing updates, you can disable
the sending of routing updates on specified interfaces by configuring the passive-interface
command. See the discussion on filtering in the “Filter Routing Information” section in the
“Configuring IP Routing Protocol-Independent Features” chapter.
Apply Offsets to Routing Metrics
An offset list is the mechanism for increasing incoming and outgoing metrics to routes learned via
RIP. This is done to provide a local mechanism for increasing the value of routing metrics.
Optionally, you can limit the offset list with either an access list or an interface. To increase the value
of routing metrics, use the following command in router configuration mode:
router rip
version 1 or 2 ( 1 is default)
network X.X.X.X ( X=IP address)
no auto-summary
Adjust Timers
Routing protocols use 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. You can
make the following timer adjustments:
• 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 routing table
• The amount of time for which routing updates will be postponed
It also is possible to tune the IP routing support in the software to enable faster convergence of the
various IP routing algorithms, and, hence, quicker fallback to redundant routers. The total effect is
to minimize disruptions to end users of the network in situations where quick recovery is essential.
To adjust the timers, use the following command in router configuration mode:
Specify a RIP Version
Cisco’s implementation of RIP Version 2 supports authentication, key management, route
summarization, classless interdomain routing (CIDR), and variable-length subnet masks (VLSMs).
Key management and VLSM are described in the chapter “Configuring IP Routing
Protocol-Independent Features.”
By default, the software receives RIP Version 1 and Version 2 packets, but sends only Version 1
packets. You can configure the software to receive and send only Version 1 packets. Alternatively,
you can configure the software to receive and send only Version 2 packets. To do so, use the
following command in router configuration mode:
Command Purpose
offset-list [access-list-number | name] {in | out} offset
[type number]
Apply an offset to routing metrics.
Command Purpose
timers basic update invalid holddown flush [sleeptime] Adjust routing protocol timers.
Command Purpose
version {1 | 2} Configure the software to receive and send only
RIP Version 1 or only RIP Version 2 packets.
The preceding task controls the default behavior of RIP. You can override that behavior by
configuring a particular interface to behave differently. To control which RIP version an interface
sends, use one of the following commands in interface configuration mode:
Similarly, to control how packets received from an interface are processed, use one of the following
commands in interface configuration mode:
Enable or Disable Split Horizon
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. However, with nonbroadcast networks (such as
Frame Relay and SMDS), situations can arise for which this behavior is less than ideal. For these
situations, you might want to disable split horizon. This applies to IGRP and RIP.
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.
To enable or disable split horizon, use one of the following commands in interface configuration
mode:
Split horizon for Frame Relay and SMDS encapsulation is disabled by default. Split horizon is not
disabled by default for interfaces using any of the X.25 encapsulations. For all other encapsulations,
split horizon is enabled by default.
See the “Split Horizon Examples” section at the end of this chapter for examples of using split
horizon.
Note In general, changing the state of the default is not recommended unless you are certain that
your application requires making a change in order to advertise routes properly. Remember: 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.
ip split-horizon :Enable split horizon.
no ip split-horizon :Disable split horizon.
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