Ip Unicast Policy Routing Overview - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide
Chapter 12 IP Unicast Policy Routing

12.1 IP Unicast Policy Routing Overview

IP policy routing is a mechanism in which packets are transmitted and forwarded by
strategy without going through the routing table. It is a more flexible routing mechanism,
compared with routing according to the destination address of data packet.
When a router is forwarding a packet, it is filtered via a route-policy first, deciding
which packets to be forwarded and the next hop.
Policy routing is configured by the user. It is composed of a group of if-match clauses
and a group of apply clauses. When some packets fully satisfy the if-match clauses of
strategy, the apply clauses in the strategy are executed in a certain sequence, to
complete the packet forwarding.
Route-policies are used for policy routing. One route-policy may contain multiple nodes,
each consisting of multiple if-match and apply clauses.
The if-match clauses of a route-policy node define the match rules whereas its apply
clauses define the actions performed on the packets filtered in by the node.
For a route-policy node, the relationship between its if-match clauses is AND for packet
filtering, meaning a packet is permitted by the node only when it matches all if-match
clauses.
At present, two if-match clauses i.e. if-match packet-length and if-match acl are
provided.
The apply clause defines the operation of the policy. At present, there are five apply
clauses: apply ip-precedence, apply output-interface, apply ip-address next-hop,
apply default output-interface, and apply ip-address default next-hop. When all
the if-match clauses are satisfied, the operation defined by the apply clauses are as
follows:
Configuring the priority: apply ip-precedence. Once configured, this clause is
executed.
Configuring the outbound interface and next hop: apply output-interface and
apply ip-address next-hop, where the apply output-interface clause has a
higher priority than the apply ip-address next-hop clause. When both of them
are configured and valid, the system executes only the apply output-interface
clause.
Configuring the default outbound interface and next hop: apply default
output-interface and apply ip-address default next-hop. The apply default
Chapter 12 IP Unicast Policy Routing Configuration
Configuration
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