User Manual

Route Import and Export Policy Overview
238 Enterasys X-Pedition User Reference Manual
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.
Import Policies
Import policies control the importation of routes from routing protocols and their installation in the
routing databases (Routing Information Base and Forwarding Information Base). Import Policies
determine which routes received from other systems are used by the XP routing process. Every
import policy can have up to two components:
•Import-Source
Table 11. Default Preference Values
Preference Defined by CLI Command Default
Direct connected networks
ip-router global set interface
0
OSPF routes
ospf
10
Static routes from config
ip add route
60
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
bgp set preference
170