IGRP Commands

Syntax Description

This command has no arguments or keywords.

Defaults

Varies with media

Command Modes

Interface configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

Note   For networks that include links over X.25 packet-switched networks (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 want to enable it, use the ip split-horizon command to restore the split horizon mechanism.

Note   In general, changing the state of the default for the ip split-horizon command is not recommended, unless you are certain that your application requires a change in order 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 routers and access servers in any relevant multicast groups on that network.

Examples

The following simple example disables split horizon on a serial link. The serial link is connected to an X.25 network:

interface serial 0
 encapsulation x25
 no ip split-horizon

Related Commands

Command	Description
network (IGRP)	Specifies a list of networks for the IGRP or Enhanced IGRP routing process.

Syntax Description

This command has no arguments or keywords.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

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 the no metric holddown command. 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 15
 network 131.108.0.0
 network 192.31.7.0
 no metric holddown

Related Commands

Command	Description
metric maximum-hops	Causes the IP routing software to advertise as unreachable those routes with a hop count higher than is specified by the command (IGRP only).
metric weights (IGRP and Enhanced IGRP)	Allows the tuning of the IGRP or IP Enhanced IGRP metric calculations.
timers basic (IGRP)	Adjusts IGRP network timers.

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

Release	Modification
10.0	This command was introduced.

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 71
 network 15.0.0.0
 metric maximum-hops 200

Related Commands

Command	Description
metric holddown	Keeps new IGRP routing information from being used for a certain period of time.
metric weights (IGRP and Enhanced IGRP)	Allows the tuning of the IGRP or IP Enhanced IGRP metric calculations.

Syntax Description

ip-address

IP address of a peer router with which routing information will be exchanged.

Defaults

No neighboring routers are defined.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

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 109
 network 131.108.0.0
 passive-interface ethernet 1
 neighbor 131.108.20.4

Related Commands

Command	Description
passive-interface	Disables sending routing updates on an interface.

Syntax Description

network-number

IP address of the directly connected networks.

Defaults

No networks are specified.

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

The network number specified must not contain any subnet information. There is no limit to the number of network commandsyou can use on the router.

IGRP or Enhanced IGRP sends updates to the interfaces in the specified networks. 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 109
 network 131.108.0.0
 network 192.31.7.0

Related Commands

Command	Description
router igrp	Configures the IGRP routing process.

Syntax Description

access-list-number | name	Standard access list number or name to be applied. Access list number 0 indicates all access lists. If offset is 0, no action is taken. For IGRP, the offset is added to the delay component only.
in	Applies the access list to incoming metrics.
out	Applies the access list to outgoing metrics.
offset	Positive offset to be applied to metrics for networks matching the access list. If the offset is 0, no action is taken.
type	(Optional) Interface type to which the offset-list is applied.
number	(Optional) Interface number to which the offset-list is applied.

Defaults

Disabled

Command Modes

Router configuration

Command History

Release	Modification
10.0	This command was introduced.
10.3	The following arguments were added: type number
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 10
 

In the following example, the router applies an offset of 10 to routes learned from Ethernet interface 0:

offset-list 21 in 10 ethernet 0

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

Release	Modification
10.0	This command was introduced.

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 109

Related Commands

Command	Description
network (IGRP)	Specifies a list of networks for the IGRP or Enhanced IGRP routing process.

Syntax Description

bandwidth	Metric value or IGRP bandwidth of the route in kilobits per second. It can be in the range 0 to 4294967295.
delay	Route delay in tens of microseconds. It can be in the range 0 to 4294967295.
reliability	Likelihood of successful packet transmission expressed as a number between 0 and 255. The value 255 means 100 percent reliability; 0 means no reliability.
loading	Effective bandwidth of the route expressed as a number from 0 to 255 (255 is 100 percent loading).
mtu	Minimum maximum transmission unit (MTU) size of the route in bytes. It can be in the range 0 to 4294967295.

Defaults

No metric will be set in the route map.

Command Modes

Route-map configuration

Command History

Release	Modification
10.0	This command was introduced.

Usage Guidelines

Note   We recommend you consult your Cisco technical support representative before changing the default value.

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.

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 1500

Syntax Description

update	Rate in seconds at which updates are sent. This is the fundamental timing parameter of the routing protocol.
invalid	Interval of time in seconds after which a route is declared invalid; it should be at least three times the value of update. A route becomes invalid when there is an absence of updates that refresh the route. The route then enters holddown. The route is marked inaccessible and advertised as unreachable. However, the route is still used for forwarding packets.
holddown	Interval in seconds during which routing information regarding better paths is suppressed. It should be at least three times the value of update. A route enters into a holddown state when an update packet is received that indicates the route is unreachable. The route is marked inaccessible and advertised as unreachable. However, the route is still used for forwarding packets. When holddown expires, routes advertised by other sources are accepted and the route is no longer inaccessible.
flush	Amount of time in seconds that must pass before the route is removed from the routing table; the interval specified must be at least the sum of invalid and holddown. If it is less than this sum, the proper holddown interval cannot elapse, which results in a new route being accepted before the holddown interval expires.
sleeptime	(Optional) Interval in milliseconds for postponing routing updates in the event of a flash update. The sleeptime value should be less than the update time. If the sleeptime is greater than the update time, routing tables will become unsynchronized.

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

Release	Modification
10.0	This command was introduced.

Usage Guidelines

The basic timing parameters for IGRP are adjustable. Because 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   The current and default timer values can be seen by inspecting the output of the show ip protocols EXEC command. The relationships of the various timers should be preserved as described previously.

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 109
 timers basic 5  15  15  30
 

Note 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.

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

Release	Modification
10.0	This command was introduced.

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 the traffic-share min command 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 5
 traffic-share min