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Each node has a match mode of permit or deny.
• permit—Specifies the permit match mode for a routing policy node. If a route matches all the
if-match clauses of the node, it is handled by the apply clauses of the node. The route does not
match against the next node unless the continue clause is configured. If a route does not
match all the if-match clauses of the node, it matches against the next node.
• deny—Specifies the deny match mode for a routing policy node. The apply and continue
clauses of a deny-mode node are never executed. If a route matches all the if-match clauses of
the node, it is discarded and does not match against the next node. If a route does not match all
the if-match clauses of the node, it matches against the next node.
A node can contain a set of if-match, apply, and continue clauses.
• if-match clauses—Configure the match criteria that match the attributes of routes. The
if-match clauses are in a logical AND relationship. A route must match all the if-match clauses
to match the node.
• apply clauses—Specify the actions to be taken on permitted routes, such as modifying a route
attribute.
• continue clause—Specifies the next node. A route that matches the current node
(permit-mode node) must match 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 only want to filter routes, do not configure apply clauses.
• If you do not configure any if-match clauses for a permit-mode node, the node will permit all
routes.
• Configure a permit-mode node containing no if-match or apply clauses behind multiple
deny-mode nodes to allow unmatched routes to pass.
Configuring filters
Configuration prerequisites
Determine the IP prefix list name, matching address range, and community list number.
Configuring an IP prefix list
Configuring an IPv4 prefix list
If all the items are set to deny mode, no routes can pass the IPv4 prefix list. To allow unmatched IPv4
routes to pass, you must configure the permit 0.0.0.0 0 less-equal 32 item following multiple deny
items.
To configure an IPv4 prefix list:
Step Command Remarks
1. Enter system view.
system-view
N/A
2. Configure an IPv4
prefix list.
ip prefix-list
prefix-list-name [
index
index-number ]
{
deny
|
permit
} ip-address mask-length
[
greater-equal
min-mask-length ] [
less-equal
max-mask-length ]
By default, no IPv4
prefix list is configured.
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