Table Of Contents
IGRP Commands
Use the commands in this chapter to configure and monitor Internet Gateway Routing Protocol (IGRP). For IGRP configuration information and examples, refer to the "Configuring IGRP" chapter of the Network Protocols Configuration Guide, Part 1.
ip split-horizon (IGRP)
To enable the split horizon mechanism, use the ip split-horizon interface configuration command. To disable the split horizon mechanism, use the no form of this command.
ip split-horizon
no ip split-horizon
Syntax Description
This command has no arguments or keywords.
Defaults
Varies with media
Command Modes
Interface configuration
Command History
Usage Guidelines
For all interfaces except those for which either Frame Relay or SMDS encapsulation is enabled, the default condition for this command is ip split-horizon; in other words, the split horizon feature is active. If the interface configuration includes either the encapsulation frame-relay or encapsulation smds commands, then the default is for split horizon to be disabled. Split horizon is not disabled by default for interfaces using any of the X.25 encapsulations.
Note
For networks that include links over X.25 PSNs, the neighbor router configuration command can be used to defeat the split horizon feature. You can as an alternative explicitly specify the no ip split-horizon command in your configuration. However, if you do so you must similarly disable split horizon for all routers in any relevant multicast groups on that network.
If split horizon has been disabled on an interface and you wish to enable it, use the ip split-horizon command to restore the split horizon mechanism.
Note
Examples
The following simple example disables split horizon on a serial link. The serial link is connected to an X.25 network:
interface serial 0encapsulation x25no ip split-horizonRelated Commands
metric holddown
To keep new IGRP routing information from being used for a certain period of time, use the metric holddown router configuration command. To disable this feature, use the no form of this command.
metric holddown
no metric holddown
Syntax Description
This command has no arguments or keywords.
Defaults
Disabled
Command Modes
Router configuration
Command History
Usage Guidelines
Holddown keeps new routing information from being used for a certain period of time. This can prevent routing loops caused by slow convergence. It is sometimes advantageous to disable holddown to increase the network's ability to quickly respond to topology changes; this command provides this function.
Use the metric holddown command if other routers or access servers within the IGRP autonomous system are not configured with no metric holddown. If all routers are not configured the same way, you increase the possibility of routing loops.
Examples
The following example disables metric holddown:
router igrp 15network 131.108.0.0network 192.31.7.0no metric holddownRelated Commands
metric maximum-hops
To have the IP routing software to advertise as unreachable those routes with a hop count higher than is specified by the command (IGRP only), use the metric maximum-hops router configuration command. To reset the value to the default, use the no form of this command.
metric maximum-hops hops
no metric maximum-hops hops
Syntax Description
hops
Maximum hop count (in decimal). The default value is 100 hops; the maximum number of hops that can be specified is 255.
Defaults
100 hops
Command Modes
Router configuration
Command History
Usage Guidelines
This command provides a safety mechanism that breaks any potential count-to-infinity problems. It causes the IP routing software to advertise as unreachable routes with a hop count greater than the value assigned to the hops argument.
Examples
In the following example, a router in autonomous system 71 attached to network 15.0.0.0 wants a maximum hop count of 200, doubling the default. The network administrators decided to do this because they have a complex WAN that can generate a large hop count under normal (nonlooping) operations.
router igrp 71network 15.0.0.0metric maximum-hops 200Related Commands
neighbor (IGRP)
To define a neighboring router with which to exchange routing information, use this form of the neighbor router configuration command. To remove an entry, use the no form of this command.
neighbor ip-address
no neighbor ip-address
Syntax Description
Defaults
No neighboring routers are defined.
Command Modes
Router configuration
Command History
Usage Guidelines
This command permits the point-to-point (nonbroadcast) exchange of routing information. When used in combination with the passive-interface router configuration command, routing information can be exchanged between a subset of routers and access servers on a LAN.
Multiple neighbor commands can be used to specify additional neighbors or peers.
Examples
In the following example, IGRP updates are sent to all interfaces on network 131.108.0.0 except interface Ethernet 1. However, in this case a neighbor router configuration command is included. This command permits the sending of routing updates to specific neighbors. One copy of the routing update is generated per neighbor.
router igrp 109network 131.108.0.0passive-interface ethernet 1neighbor 131.108.20.4Related Commands
network (IGRP)
To specify a list of networks for the Enhanced IGRP routing process, use this form of the network router configuration command. To remove an entry, use the no form of this command.
network network-number
no network network-number
Syntax Description
Defaults
No networks are specified.
Command Modes
Router configuration
Command History
Usage Guidelines
The network number specified must not contain any subnet information. You can specify multiple network commands.
IGRP or Enhanced IGRP sends updates to the interfaces in the specified network(s). Also, if an interface's network is not specified, it will not be advertised in any IGRP or Enhanced IGRP update.
Examples
The following example configures a router for IGRP and assigns autonomous system 109. The network commands indicate the networks directly connected to the router.
router igrp 109network 131.108.0.0network 192.31.7.0Related Commands
offset-list (IGRP)
To add an offset to incoming and outgoing metrics to routes learned via IGRP, use the offset-list router configuration command. To remove an offset list, use the no form of this command.
offset-list {access-list-number | name} {in | out} offset [type number]
no offset-list {access-list-number | name} {in | out} offset [type number]
Syntax Description
Defaults
Disabled
Command Modes
Router configuration
Command History
10.0
This command was introduced.
10.3
The following arguments were added:
•
•
11.2
The name argument was added.
Usage Guidelines
The offset value is added to the routing metric. An offset-list with an interface type and interface number is considered extended and takes precedence over an offset-list that is not extended. Therefore, if an entry passes the extended offset-list and the normal offset-list, the extended offset-list's offset is added to the metric.
Examples
In the following example, the router applies an offset of 10 to the router's delay component only to access list 121:
offset-list 21 out 10In the following example, the router applies an offset of 10 to routes learned from Ethernet interface 0:
offset-list 21 in 10 ethernet 0router igrp
To configure the Interior Gateway Routing Protocol (IGRP) routing process, use the router igrp global configuration command. To shut down an IGRP routing process, use the no form of this command.
router igrp autonomous-system
no router igrp autonomous-system
Syntax Description
autonomous-system
Autonomous system number that identifies the routes to the other IGRP routers. It is also used to tag the routing information.
Defaults
No IGRP routing process is defined.
Command Modes
Global configuration
Command History
Usage Guidelines
It is not necessary to have a registered autonomous system number to use IGRP. If you do not have a registered number, you are free to create your own. We recommend that if you do have a registered number, you use it to identify the IGRP process.
Examples
The following example configures an IGRP routing process and assign process number 109:
router igrp 109Related Commands
set metric (IGRP)
To set the metric value for IGRP in a route-map, use the set metric route-map configuration command. To return to the default metric value, use the no form of this command.
set metric bandwidth delay reliability loading mtu
no set metric bandwidth delay reliability loading mtu
Syntax Description
Defaults
No metric will be set in the route-map.
Command Modes
Route-map configuration
Command History
Usage Guidelines
Note
Use the route-map global configuration command, and the match and set route-map configuration commands, to define the conditions for redistributing routes from one routing protocol into another. Each route-map command has a list of match and set commands associated with it. The match commands specify the match criteria—the conditions under which redistribution is allowed for the current route-map command. The set commands specify the set actions—the particular redistribution actions to perform if the criteria enforced by the match commands are met. The no route-map command deletes the route map.
The set route-map configuration commands specify the redistribution set actions to be performed when all of a route map's match criteria are met. When all match criteria are met, all set actions are performed.
Examples
The following example sets the bandwidth to 10,000, the delay to 10, the reliability to 255, the loading to 1, and the MTU to 1500:
set metric 10000 10 255 1 1500timers basic (IGRP)
To adjust IGRP network timers, use the timers basic router configuration command. To restore the default timers, use the no form of this command.
timers basic update invalid holddown flush [sleeptime]
no timers basic
Syntax Description
Defaults
update is 90 seconds
invalid is 270 seconds
holddown is 280 seconds
flush is 630 seconds
sleeptime is 0 milliseconds
Command Modes
Router configuration
Command History
Usage Guidelines
The basic timing parameters for IGRP are adjustable. Since this routing protocol is executing a distributed, asynchronous routing algorithm, it is important that these timers be the same for all routers and access servers in the network.
Note
Examples
The following example sets updates to be broadcast every 5 seconds. If a router is not heard from in 15 seconds, the route is declared unusable. Further information is suppressed for an additional 15 seconds. At the end of the suppression period, the route is flushed from the routing table.
router igrp 109timers basic 5 15 15 30Note that by setting a short update period, you run the risk of congesting slow-speed serial lines; however, this is not a big concern on faster-speed Ethernets and T1-rate serial lines. Also, if you have many routes in your updates, you can cause the routers to spend an excessive amount of time processing updates.
traffic-share
To control how traffic is distributed among routes when there are multiple routes for the same destination network that have different costs, use the traffic-share router configuration command. To disable this function, use the no form of the command.
traffic-share {balanced | min}
no traffic-share {balanced | min}
Syntax Description
balanced
Distributes traffic proportionately to the ratios of the metrics.
min
Uses routes that have minimum costs.
Defaults
Traffic is distributed proportionately to the ratios of the metrics.
Command Modes
Router configuration
Command History
Usage Guidelines
This command applies to IGRP and Enhanced IGRP routing protocols only. With the default setting, routes that have higher metrics represent less-preferable routes and get less traffic. Configuring traffic-share min causes the Cisco IOS software to only divide traffic among the routes with the best metric. Other routes will remain in the routing table, but will receive no traffic.
Examples
In the following example, only routes of minimum cost will be used:
router igrp 5traffic-share min
