Routing; Introduction To Routing Policy - 3Com Switch 4800G 24-Port Configuration Manual

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Introduction to
Routing Policy
Routing Policy
Filters
R P
OUTING
A routing policy is used on the router for route inspection, filtering, attributes
modifying when routes are received, advertised, or redistributed.
When distributing or receiving routing information, a router can use a routing
policy to filter routing information. For example, a router receives or advertises
only routing information that matches the criteria of a routing policy; a routing
protocol redistributes routes from another protocol only routes matching the
criteria of a routing policy and modifies some attributes of these routes to satisfy
its needs using the routing policy.
To implement a routing policy, you need to define a set of match criteria according
to attributes in routing information, such as destination address, advertising
router's address and so on. The match criteria can be set beforehand and then
apply them to a routing policy for route distribution, reception and redistribution.
Routing protocols can use six filters: ACL, IP prefix list, AS path ACL, community
list, extended community list and routing policy.
ACL
When defining an ACL, you can specify IP addresses and prefixes to match
destinations or next hops of routing information.
For ACL configuration, refer to "IPv6 ACL Configuration" on page 851.
IP prefix list
IP prefix list plays a role similar to ACL, but it is more flexible than ACL and easier
to understand. When an IP prefix list is applied to filtering routing information, its
matching object is the destination address of routing information.
An IP prefix list is identified by name. Each IP prefix list can comprise multiple
items, and each item, which is identified by an index number, can specify a
matching range in the network prefix format. The index number indicates the
matching sequence of items in the IP prefix list.
During matching, the router compares the packet with the items in the ascending
order. If one item is matched, the IP prefix list filter is passed, and the packet will
not go to the next item.
C
OLICY ONFIGURATION