
IP Concepts, Terminology, and Features
308627-14.20 Rev 00
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Route Preferences
The IP router maintains an internal routing table. When determining how to
forward a datagram, the IP router consults the table to determine the specific route
that a datagram should take. A routing table can contain direct routes for the IP
router’s network interfaces, static routes, and any routes learned from RIP, OSPF,
BGP, or EGP. (Information about adjacent hosts is maintained in a separate table.)
Preferences determine what goes into the routing table. Multiple routes to the
same destination may exist in the table. Preference values range from 1 (lowest)
through 16 (highest).
By default, RIP, BGP, EGP, and OSPF external routes have a preference value of
1. Static routes, direct routes, and OSPF intra-area and interarea routes have a
default preference value of 16.
You can configure a preference value from 1 through 16 for RIP, BGP, EGP, OSPF
external, and static routes. You cannot configure a preference value for direct
routes and OSPF intra-area and interarea routes.
To assign a preference value to a route learned by RIP, OSPF, BGP, or EGP, you
configure an accept policy for the route (see “
IP Routing Policies and Filters” on
page 1-23). If an incoming route matches the policy, IP assigns the preference
value that you specify to the route and considers the route for possible inclusion in
the routing table.
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