Filtering during redistribution

Filtering during redistribution
EIGRP AS 100
R1
OPSF 1
Area 0
196.100.100.0 /24 172.16.168.0 /24 192.168.100.0 /24 192.168.200.0 /24
196.15.40.0 /24 192.168.24.0 /24
R2 R5
R3 R4 R6 R7
352 Chapter 10  Route Optimization
In this example, we will redistribute the routes contained in EIGRP AS 100 into OSPF 1.
However, we do not want the route 192.168.200.0 /24 redistributed into OSPF 1. We do want
all other routes and any future routes to be redistributed. First, we need to create a route map
that will deny that route and permit all other routes. We will then configure the redistribution
and include the route map:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#access-list 1 permit 192.168.200.0 0.0.0.255
R1(config)#route-map EIGRPTOOSPF deny 10
R1(config-route-map)#match ip address 1
R1(config-route-map)#route-map EIGRPTOOSPF permit 20
R1(config-route-map)#exit
R1(config)#router ospf 1
R1(config-router)#redistribute eigrp 100 metric 100 subnets route-map
➥EIGRPTOOSPF
R1(config-router)#^Z
R1#
That will do it. All other routes will be permitted, and 192.168.200.0 /24 will be denied.
Now that you understand how to filter routes with route maps for redistribution, let’s build
on it. This time, we still want to block route 192.168.200.0 /24 and set the metric of route
192.168.100.0 /24 to 150, and for any future routes, we want their metric to be set to 100:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#access-list 1 permit 192.168.200.0 0.0.0.255
R1(config)#access-list 2 permit 192.168.100.0 0.0.0.255
R1(config)#route-map EIGRPTOOSPF deny 10
R1(config-route-map)#match ip address 1
R1(config-route-map)#route-map EIGRPTOOSPF permit 20
R1(config-route-map)#match ip address 2
R1(config-route-map)#set metric 150
R1(config-route-map)#route-map EIGRPTOOSPF permit 30
R1(config-route-map)#set metric 100
R1(config-route-map)#exit
R1(config)#router ospf 1
R1(config-router)#redistribute eigrp 100 metric 100 subnets route-map
➥EIGRPTOOSPF
R1(config-router)#^Z
R1#
Summarization 353
Here’s a breakdown of what will occur:
1. 192.168.200.0 /24 will match the statement contained in sequence 10. Because sequence 10
is a deny sequence, the route will not be redistributed.
2. 192.168.100.0 /24 will match the statement contained in sequence 20. Since the condition
says to set the metric to 150, the route’s metric will be set to 150. The route is redistributed
because the sequence is a permit.
3. All other routes will be accepted by sequence 30 since no match statement was specified.
The metric of all the routes will be set to 100 as specified by the set metric action, and
then all routes will be redistributed because the sequence is a permit.
Using route maps with redistribution is an important concept to grasp. They are used
frequently in the real world. In order to master the concepts of redistribution and redistribution
with route maps, you need to spend time practicing using them. It will help you in
the long run.