Using Multiple Routing Protocols

There are several reasons you may need to run multiple routing protocols in your network. Some include:

■ Migrating from one routing protocol to another, where both protocols will ran in the network temporarily

■ Applications that run under certain routing protocols but not others a Areas of the network under different administrative control ("layer 8" issues)

■ A multi-vendor environment in which some parts of the network require a standards-based protocol

CCNP BSC) Quick Reference Sheets

Configuring Route Redistribution

If routing information must be exchanged among the different protocols or routing domains, redistribution can be used. Only routes that are in the routing table and learned via the specified protocol are redistributed. Each protocol has some unique characteristics when redistributing, as shown in Table 5-1.

TABLE 5-1 Route Redistribution Characteristics

Protocol

Redistribution Characteristics

RIP

Metric must be set, except when redistributing

static or connected routes, which have a metric of I.

OSPF

Default metric is 20. Can specify the metric type:

the default is E2. Must use subnets keyword or only

classful networks are redistributed.

EIGRP

Metric must be set, except when redistributing

static or connected routes, which get their metric

from the interface. Metric value is "bandwidth.

delay, reliability, load, MTU." Redistributed routes

have a higher administrative distance than internal

ones.

IS-IS

Default metric is 0. Can specify route level: default

is L2. Can choose to redistribute only external or

internal routes into IS- IS from OSPF and into

OSPF from IS-IS.

Static/Connected To include local networks not running the routing protocol, you must redistribute connected inter faces. You can also redistribute static routes into a dynamic protocol.

Static/Connected To include local networks not running the routing protocol, you must redistribute connected inter faces. You can also redistribute static routes into a dynamic protocol.

© 2007 Cisco Systems Inc. Ail rights reserved. This publication is protected by copyright. Please see page 73 for more details.

CHAPTER 5

OPTIMIZING ROUTING

You can redistribute only between protocols that use the same protocol stack, such as IP protocols, which cannot advertise IPX routes. To configure redistribution, issue this command under the routing process that is to receive the new routes:

Router)corfig-router)#redistribute (route-source) [metric metric] [route-map tag]

Seed Metric

Redistribution involves configuring a routing protocol to advertise routes learned by another routing process. Normally, protocols base their metric on an interface value, such as bandwidth, but 110 interface for a redistributed route exists. Protocols use incompatible metrics, so the redistributed routes must be assigned a new metric compatible with the new protocol.

A route's starting metric is called its seed metric. Set the seed metric for all redistributed routes with the default-metric [metric] command under the routing process. To set the metric for specific routes, either use the metric keyword when redistributing or use the route-map keyword to link a route map to the redistribution. After the seed metric is specified, it increments normally as the route is advertised through the network (except for certain OSPF routes).

CCNP 8SC1 Quick Reference Sheets

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