Cabletron Systems 9032578-05 manual Multi-Exit Discriminator Attribute Example

Chapter 12: BGP Configuration Guide

For example, in Figure 14, routers SSR12, SSR13, and SSR14 have the following line in their CLI configuration files:

bgp set peer-group as901 set-pref 100

•The value of the set-prefoption should be consistent with the import policy in the network.

The metric value should be set high enough to avoid conflicts between BGP routes and IGP or static routes. For example, if the import policy sets GateD preferences ranging from 170 to 200, a set-pref metric of 170 would make sense. You should set the metric high enough to avoid conflicts between BGP routes and IGP or static routes.

Multi-Exit Discriminator Attribute Example

Multi-Exit Discriminator (MED) is a BGP attribute that affects the route selection process. MED is used on external links to discriminate among multiple exit or entry points to the same neighboring AS. All other factors being equal, the exit or entry point with a lower metric should be preferred. If received over external links, the MED attribute may be propagated over internal links to other BGP speakers within the same AS. The MED attribute is never propagated to other BGP speakers in neighboring autonomous systems.

Figure 15 shows a sample BGP configuration where the MED attribute has been used.

SSR4

10.200.12.4/24

172.16.200.4/24

172.16.200.6/24

SSR6

AS 64752

10.200.12.6/24 N1

10.200.12.0/24

10.200.12.15/24

C1

Legend:		AS 64751
	Physical Link

Peering Relationship

Information Flow

Figure 15. Sample BGP Configuration (MED Attribute)

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