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Table of Contents

IGRP Commands

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.

default-information

To control the candidate default routing information between IGRP or Enhanced IGRP processes, use the default-information router configuration command. To suppress IGRP or Enhanced IGRP candidate information in incoming updates, use the no default-information in command. To suppress IGRP or Enhanced IGRP candidate information in outbound updates, use the no default-information out command.

default-information {in | out} {access-list-number | name}
no default-information {in | out}

Syntax Description

in

Allows IGRP or Enhanced IGRP exterior or default routes to be received by an IGRP process.

out

Allows IGRP or Enhanced IGRP exterior routes to be advertised in updates.

access-list-number | name

Number or name of an access list. It can be a number in the range 1 to 99 or an access list name.

Default

Normally, exterior routes are always accepted and default information is passed between IGRP or Enhanced IGRP processes when doing redistribution.

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0. The access-list-number and name arguments first appeared in Cisco IOS Release 11.2.

The default network of 0.0.0.0 used by RIP cannot be redistributed by IGRP or Enhanced IGRP.

Examples

The following example allows IGRP exterior or default routes to be received by the IGRP process in autonomous system 23:

router igrp 23
  default-information in

The following example allows IP Enhanced IGRP exterior or default routes to be received by the IP Enhanced IGRP process in autonomous system 23:

router eigrp 23
  default-information in

default-metric (IGRP and Enhanced IGRP only)

To set metrics for IGRP or Enhanced IGRP, use this form of the default-metric router configuration command. To remove the metric value and restore the default state, use the no form of this command.

default-metric bandwidth delay reliability loading mtu
no default-metric bandwidth delay reliability loading mtu

Syntax Description

bandwidth

Minimum bandwidth of the route in kilobits per second. It can be 0 or any positive integer.

delay

Route delay in tens of microseconds. It can be 0 or any positive number that is a multiple of 39.1 nanoseconds.

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 0 or any positive integer.

Default

Only connected routes and interface static routes can be redistributed without a default metric.

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

A default metric is required to redistribute a protocol into IGRP or Enhanced IGRP, unless you use the redistribute command. Automatic metric translations occur between IGRP and Enhanced IGRP. You do not need default metrics to redistributed IGRP or Enhanced IGRP into itself.

Metric defaults have been carefully set to work for a wide variety of networks. Take great care in changing these values.

Keeping the same metrics is supported only when redistributing from IGRP, Enhanced IGRP, or static routes.

Example

The following example takes redistributed RIP metrics and translates them into IGRP metrics with values as follows: bandwidth = 1000, delay = 100, reliability = 250, loading = 100, and mtu =1500.

router igrp 109
  network 131.108.0.0
  redistribute rip
  default-metric 1000 100 250 100 1500

Related Commands

You can use the master indexes or search online to find documentation of related commands.

redistribute

ip split-horizon

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.

Default

Varies with media

Command Mode

Interface configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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 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.

Example

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

You can use the master indexes or search online to find documentation of related commands.

neighbor

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.

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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.

Example

The following example disables metric holddown:

router igrp 15
  network 131.108.0.0
  network 192.31.7.0
  no metric holddown

Related Commands

You can use the master indexes or search online to find documentation of related commands.

metric maximum-hops
metric weights
timers basic

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.

Default

100 hops

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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.

Example

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

You can use the master indexes or search online to find documentation of related commands.

metric holddown
metric weights

metric weights

To allow the tuning of the IGRP or Enhanced IGRP metric calculations, use the metric weights router configuration command. To reset the values to their defaults, use the no form of this command.

metric weights tos k1 k2 k3 k4 k5
no metric weights

Syntax Description

tos

Type of service. Currently, it must always be zero.

k1-k5

Constants that convert an IGRP or Enhanced IGRP metric vector into a scalar quantity.

Defaults

tos: 0
k1: 1
k2: 0
k3: 1
k4: 0
k5: 0

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

Use this command to alter the default behavior of IGRP routing and metric computation and allow the tuning of the IGRP metric calculation for a particular type of service (TOS).

If k5 equals 0, the composite IGRP or enhanced IGRP metric is computed according to the following formula:

metric = [k1 * bandwidth + (k2 * bandwidth)/(256 - load) + k3 * delay]

If k5 does not equal zero, an additional operation is done:

metric = metric * [k5 / (reliability + k4)]

Bandwidth is inverse minimum bandwidth of the path in bits per second scaled by a factor of 2.56  ¥  1012. The range is from a 1200-bps line to 10 terabits per second.

Delay is in units of 10 microseconds. This gives a range of 10 microseconds to 168 seconds. A delay of all ones indicates that the network is unreachable.

The delay parameter is stored in a 32-bit field, in increments of 39.1 nanoseconds. This gives a range of 1 (39.1 nanoseconds) to hexadecimal FFFFFFFF (decimal 4,294,967,040 nanoseconds). A delay of all ones (that is, a delay of hexadecimal FFFFFFFF) indicates that the network is unreachable.

Table 22 lists the default values used for several common media.


Table 22: Bandwidth Values by Media Type
Media Type Delay Bandwidth

Satellite

5120 (2 seconds)

5120 (500 Mbits)

Ethernet

25600 (1 ms)

256000 (10 Mbits)

1.544 Mbps

512000 (20,000 ms)

1,657,856 bits

64 kbps

512000 (20,000 ms)

40,000,000 bits

56 kbps

512000 (20,000 ms)

45,714,176 bits

10 kbps

512000 (20,000 ms)

256,000,000 bits

1 kbps

512000 (20,000 ms)

2,560,000,000 bits

Reliability is given as a fraction of 255. That is, 255 is 100 percent reliability or a perfectly stable link.

Load is given as a fraction of 255. A load of 255 indicates a completely saturated link.

Example

The following example sets the metric weights to slightly different values than the defaults:

router igrp 109
  network 131.108.0.0
  metric weights 0 2 0 2 0 0

Related Commands

You can use the master indexes or search online to find documentation of related commands.

bandwidth
delay

metric holddown
metric maximum-hops

neighbor (IGRP and RIP)

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

ip-address

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

Default

No neighboring routers are defined.

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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.

Example

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

You can use the master indexes or search online to find documentation of related commands.

passive-interface

network (IGRP and Enhanced 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

network-number

IP address of the directly connected networks.

Default

No networks are specified.

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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.

Example

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

You can use the master indexes or search online to find documentation of related commands.

router igrp

offset-list

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

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.

Default

Disabled

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0. The type and number arguments first appeared in Cisco IOS Release 10.3. The name argument first appeared in Cisco IOS Release 11.2.

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

router 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.

Default

No IGRP routing process is defined.

Command Mode

Global configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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.

Example

The following example configures an IGRP routing process and assign process number  109:

router igrp 109

Related Commands

You can use the master indexes or search online to find documentation of related commands.

network (IGRP and Enhanced IGRP)

set metric

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

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.

Default

No metric will be set in the route-map.

Command Mode

Route-map configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.


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.

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.

Example

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

timers basic

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

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 Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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 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.

Example

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.

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.

Default

Traffic is distributed proportionately to the ratios of the metrics.

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

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.

Example

In the following example, only routes of minimum cost will be used:

router igrp 5
  traffic-share min

validate-update-source

To have the Cisco IOS software validate the source IP address of incoming routing updates for RIP and IGRP routing protocols, use the validate-update-source router configuration command. To disable this function, use the no form of this command.

validate-update-source
no validate-update-source

Syntax Description

This command has no arguments or keywords.

Default

Enabled

Command Mode

Router configuration

Usage Guidelines

This command first appeared in Cisco IOS Release 10.0.

This command is only applicable to RIP and IGRP. The software ensures that the source IP address of incoming routing updates is on the same IP network as one of the addresses defined for the receiving interface.

Disabling split horizon on the incoming interface will also cause the system to perform this validation check.

For unnumbered IP interfaces (interfaces configured as ip unnumbered), no checking is performed.

Example

The following example configures a router not to perform validation checks on the source IP address of incoming RIP updates:

router rip
  network 128.105.0.0
  no validate-update-source


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