
Configuring IP Services
1-14
IP Routing Policies and Filters
The IP router allows you to control the flow of routing data to and from the
routing tables. This control is provided by two mechanisms:
• IP accept and announce policies
• Import and export filters
IP accept policies (and the subset of parameters provided by import filters) govern
the addition of new RIP-, OSPF-, BGP-, or EGP-derived routes to the routing
tables. When RIP, OSPF, BGP, or EGP receives a new routing update, it consults
its accept policies to validate the information before entering the update into the
routing tables. Accept policies contain search information (to match fields in
incoming routing updates) and action information (to specify the action to take
with matching routes).
IP announce policies (and the subset of parameters provided by export filters)
govern the propagation of RIP, OSPF, BGP, or EGP routing information. When
preparing a routing advertisement, RIP, OSPF, BGP, or EGP consults its announce
policies to determine whether the routes to specific networks are to be advertised
and how they are to be propagated. Announce policies contain network numbers
(to associate a policy with a specific network) and action information (to specify a
route propagation procedure).
IP accept and announce policies and policy parameters are described in Chapter 9.
IP import and export filters and filter parameters are described in Chapter 10.
Note: Accept and announce policies provide a superset of the parameters
provided by import and export filters. We currently support both IP policies
and IP route filters. However, network administrators using import and export
filters for routing table management should migrate as quickly as possible to
IP policies. In a future release, support for import and export filters will be
discontinued.
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