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Route Import and Export Policy Overview

182 Enterasys Xpedition User Reference Manual

Preference

Preference is the value the XP routing process uses to order preference of routes from one

protocol or peer over another. Preference can be set using several different configuration

commands. Preference can be set based on one network interface over another, from one

protocol over another, or from one remote gateway over another. Preference may not be

used to control the selection of routes within an Interior Gateway Protocol (IGP). This is

accomplished automatically by the protocol based on metric.

Preference may be used to select routes from the same Exterior Gateway Protocol (EGP)

learned from different peers or autonomous systems. Each route has only one preference

value associated with it, even though the preference can be set at many places using

configuration commands. The last or most specific preference value set for a route is the

value used. A preference value is an arbitrarily assigned value used to determine the

order of routes to the same destination in a single routing database. The active route is

chosen by the lowest preference value.

A default preference is assigned to each source from which the XP routing process

receives routes. Preference values range from 0 to 255 with the lowest number indicating

the most preferred route.

The following table summarizes the default preference values for routes learned in

various ways. The table lists the CLI commands that set preference, and shows the types

of routes to which each CLI command applies. A default preference for each type of route

is listed, and the table notes preference precedence between protocols. The narrower the

scope of the statement, the higher precedence its preference value is given, but the smaller

the set of routes it affects.

Table 9. Default Preference Values

Preference Defined by CLI Command Default

Direct connected networks

ip-router global set interface

OSPF routes

ospf

Static routes from config

ip add route

RIP routes

rip set preference

100

Point-to-point interface 110

Routes to interfaces that are

down

ip-router global set interface down-preference

120

Aggregate/generate routes

aggr-gen

130

OSPF AS external routes

ospf set ase-defaults preference

150

BGP routes

/jointfilesconvert/276250/bgp set preference

170

1 2 ... 197 198 199 200 201 202 203 204 205 206 207 ... 393 394

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