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Routing policy
A routing policy can contain multiple nodes, which are in a logical OR relationship. A node with a
smaller number is matched first. A route matches the routing policy if it matches one node (except
the node configured with the continue clause) in the routing policy.
Each node has a match mode of permit or deny.
• permit—Specifies the permit match mode for a routing policy node. If a route meets all the
if-match clauses of the node, it is handled by the apply clauses of the node. The route is not
compared with the next node unless the continue clause is configured. If a route does not meet
all the if-match clauses of the node, it is compared with the next node.
• deny—Specifies the deny match mode for a routing policy node. The apply and continue
clauses of a deny node are never executed. If a route meets all the if-match clauses of the
node, it is denied without being compared with the next node. If a route does not meet all the
if-match clauses of the node, it is compared with the next node.
A node can contain a set of if-match, apply, and continue clauses.
• if-match clauses—Specify the match criteria that match the attributes of routes. The if-match
clauses are in a logical AND relationship. A route must meet 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 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 node, the node will permit all routes.
• Configure a permit node containing no if-match or apply clauses following multiple deny 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 permit unmatched
IPv4 routes, you must configure the permit 0.0.0.0 0 less-equal 32 item following multiple deny
items.
To configure an IPv4 prefix list:
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
By default, no IPv4
prefix lists exist.
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