
Operation Manual – IPv4 Routing
H3C S5500-EI Series Ethernet Switches
Chapter 6 Routing Policy Configuration
6-2
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.
6.1.2 Filters
Routing protocols can use six filters: ACL, IP prefix list, AS path ACL, community list,
extended community list and routing policy.
I. ACL
ACL involves IPv4 ACL only. 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
ACL configuration
.
II. 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. Moreover, you can specify the
gateway
option to indicate that only routing information advertised by certain routers
will be received.
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.
III. AS-path
AS path is only applicable to BGP. There is an AS-path field in the BGP packet. An AS
path list specifies matching conditions according to the AS-path field.
IV. Community list
Community list only applies to BGP. The BGP packet contains a community attribute
field to identify a community. A community list specifies matching conditions based on
the community attribute.