Cisco Systems 78-11741-02 manual Understanding Supported Metric Translations, IPC-369

Configuring IP Routing Protocol-Independent Features

Redistributing Routing Information

Command	Purpose
Router(config-route-map)# set metric-type internal	Sets the Multi Exit Discriminator (MED) value on
	prefixes advertised to Exterior BGP neighbor to match
	the Interior Gateway Protocol (IGP) metric of the next
	hop.
Router(config-route-map)# set tag tag-value	Sets the tag value to associate with the redistributed
	routes.

See the “BGP Route Map Examples” section in the “Configuring BGP” chapter for examples of BGP route maps. See the “BGP Community with Route Maps Examples” section in the “Configuring BGP” chapter for examples of BGP communities and route maps.

To distribute routes from one routing domain into another and to control route redistribution, use the following commands in router configuration mode:

	Command	Purpose
Step 1
	Router(config-router)# redistribute protocol	Redistributes routes from one routing protocol to
	[process-id]{level-1 level-1-2 level-2} [metric	another routing protocol.
	metric-value][metric-typetype-value] [match
	internal external type-value] [tag tag-value]
	[route-map map-tag] [subnets]
Step 2
	Router(config-router)# default-metricnumber	Causes the current routing protocol to use the same
		metric value for all redistributed routes (BGP, OSPF,
		RIP).
Step 3
	Router(config-router)# default-metricbandwidth	Causes the IGRP or Enhanced IGRP (EIGRP) routing
	delay reliability loading mtu	protocol to use the same metric value for all
		non-IGRP redistributed routes.
Step 4
	Router(config-router)#no default-information {in	Disables the redistribution of default information
	out}	between IGRP processes, which is enabled by
		default.

The metrics of one routing protocol do not necessarily translate into the metrics of another. For example, the RIP metric is a hop count and the IGRP metric is a combination of five quantities. In such situations, an artificial metric is assigned to the redistributed route. Because of this unavoidable tampering with dynamic information, carelessly exchanging routing information between different routing protocols can create routing loops, which can seriously degrade network operation.

Understanding Supported Metric Translations

This section describes supported automatic metric translations between the routing protocols. The following descriptions assume that you have not defined a default redistribution metric that replaces metric conversions:

•RIP can automatically redistribute static routes. It assigns static routes a metric of 1 (directly connected).

•BGP does not normally send metrics in its routing updates.

Cisco IOS IP Configuration Guide

IPC-369