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An IP prefix list is configured to match the destination address of routing information. You can use the
gateway
option to allow only routing information from certain routers to be received. For
gateway
option
information, see "Configuring RIP" and "Configuring OSPF."
An IP prefix list, identified by name, can comprise multiple items. Each item, identified by an index
number, can specify a prefix range to match. An item with a smaller index number is matched first. If one
item is matched, the IP prefix list is passed, and the packet will not go to the next item.
AS path list
An AS path list, configured based on the BGP AS_PATH attribute, can only be used to match BGP routing
information.
For more information about AS path list, see "Configuring BGP."
Community list
A community list, configured based on the BGP COMMUNITY attribute, can only be used to match BGP
routing information.
For more information about community list, see "Configuring BGP."
Extended community list
An extended community list, configured based on the BGP extended community attribute (Route-Target
for VPN and Source of Origin), can only be used to match BGP routing information.
Routing policy
A routing policy is used to match routing information and modify the attributes of permitted routes. It can
reference the filters to define its own match criteria.
A routing policy can comprise multiple nodes, which are in logic OR relationship. Each routing policy
node is a match unit, and a node with a smaller number is matched first. Once a node is matched, the
routing policy is passed and the packet will not go to the next node.
A routing policy node comprises a set of
if-match
,
apply
, and
continue
clauses.
•
The
if-match
clauses define the match criteria. The matching objects are some attributes of routing
information. The
if-match
clauses of a routing policy node is in a logical AND relationship. A
packet must match all the
if-match
clauses of the node to pass it.
•
The
apply
clauses of the node specify the actions to be taken on the permitted packets, such as
modifying a route attribute.
•
The
continue
clause specifies the next routing policy node to be matched. With this clause
configured, when a route matches the current routing policy node, it continues to match against the
specified next node in the same routing policy. The
continue
clause combines the
if-match
and
apply
clauses of the two nodes to improve flexibility of the routing policy.
Follow these guidelines when you configure
if-match
,
apply
, and
continue
clauses:
•
If you want to implement route filtering only, you do not need to configure
apply
clauses.
•
If you do not configure any
if-match
clauses for a permit-mode node, the node permits all routes to
pass.
•
Configure a permit-mode node containing no
if-match
or
apply
clauses behind multiple deny-mode
nodes to allow unmatched routes to pass.
