Understanding the network.pdf - Back to Home

oute-map identifier, which associates the route-map with the policy route
statement.
Policy routes, like ACLs, use deny as their implicit action. If no action statement is
declared, the map sequence will be interpreted as a deny action.
The sequence number serves two roles:
• Sequence identification
• Sequence order
Route-map statements can be entered in any order, but they will be processed and
matched in sequence, starting with the lowest-numbered statement. When building
map statements, it is not a bad idea to leave numbers between statements (like old
BASIC programming) so if you want to add a statement later you can just slide it in.
Let's create a simple map to redirect Web traffic to a Web cache server:
jung(config)#route-map http permit 10
jung(config-route-map)#match ip address 113
jung(config-route-map)#set ip next-hop 172.16.84.2
NOTE
The deny action has a different effect depending on the application of the route-map.
If the map is being applied as a policy route and a datagram matches a deny
statement, the datagram is processed normally (outside of the policy route). If the
map is used for filtering a route redistribution, a deny match will not redistributed.
In the example above, the route-map
configuration subcommand is used to reference ACL 113 for matching criteria. TCP
packets that meet this criterion are forwarded to the Web cache server with the IP
address of 172.16.84.2. All other traffic is implicitly denied—in other words, is
routed normally. The operator is used to define policy route
matching criteria. Table 9.8 lists the set operators available for use with policy
routing.