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Chapter 9: Routing Policy Configuration Guide
The routes contributing to an aggregate can be identified by their associated attributes:
•
Protocol type (RIP, OSPF, BGP, Static, Direct, Aggregate).
•
Autonomous system from which the route was learned.
•
AS path associated with a route. When BGP is configured, all routes are assigned an AS
path when they are added to the routing table. For interior routes, this AS path
specifies IGP as the origin and no ASs in the AS path (the current AS is added when
the route is exported). For BGP routes, the AS path is stored as learned from BGP.
•
Tag associated with a route. Both OSPF and RIP version 2 currently support tags. All
other protocols have a tag of zero.
In some cases, a combination of the associated attributes can be specified to identify the
routes contributing to an aggregate.
Route-Filter
This component specifies the individual routes that are to be aggregated or summarized.
The preference to be associated with these routes can also be explicitly specified using this
component.
The contributing routes are ordered according to the aggregation preference that applies
to them. If there is more than one contributing route with the same aggregating
preference, the route's own preferences are used to order the routes. The preference of the
aggregate route will be that of contributing route with the lowest aggregate preference.
A route may only contribute to an aggregate route that is more general than itself; it must
match the aggregate under its mask. Any given route may only contribute to one
aggregate route, which will be the most specific configured, but an aggregate route may
contribute to a more general aggregate.
An aggregate-route only comes into existence if at least one of its contributing routes is
active.
Authentication
Authentication guarantees that routing information is only imported from trusted routers.
Many protocols like RIP V2 and OSPF provide mechanisms for authenticating protocol
exchanges. A variety of authentication schemes can be used. Authentication has two
components: an Authentication Method and an Authentication Key. Many protocols allow
different authentication methods and keys to be used in different parts of the network.
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Internet Appliance User Reference Manual
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