16-3 summary-address ip-address mask tag value

16-3 summary-address ip-address mask tag value

Syntax Description:

• ip-address ” IP address of the summary route.

• mask ” Subnet mask used to generate the summary.

• tag ” The summary route will be tagged with this value. The range of values is 0 to 4,294,967,295.

Purpose: OSPF can summarize routes that have been redistributed into OSPF. The summary can be applied to routes redistributed from a dynamic routing protocol, static, or connected routes. The router performing the redistribution is an ASBR. The summary-address command can only be used on an ASBR. Using the not-advertise keyword will suppress the advertisement of the summary route by the ASBR. Using a tag allows routing policies to be based on the tag value instead of the IP address.

Initial Cisco IOS Software Release: 10.0

Configuration Example 1: Attaching a Tag to Summarized Routes Created on an ASBR

In Figure 16-2, Router B will summarize the four networks that are being redistributed into OSPF into two summaries. Each summary will be given a different tag value. This example simulates four networks on Router B using loopback interfaces. These four networks will then be redistributed into OSPF. The router performing the redistribution is an ASBR.

Figure 16-2. Tagging Redistributed Routes

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   !   interface Serial0/1   ip address 10.1.1.1 255.255.255.252   clockrate 64000   !   router ospf 1   network 10.1.1.0 0.0.0.3 area 1  _______________________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Loopback1   ip address 156.26.32.1 255.255.255.240   !   interface Loopback2   ip address 156.26.32.17 255.255.255.240   no ip directed-broadcast   !   interface Loopback3   ip address 156.26.32.33 255.255.255.240   !   interface Loopback4   ip address 156.26.32.49 255.255.255.240   !   interface Serial0   ip address 10.1.1.2 255.255.255.252   no ip directed-broadcast   !   router ospf 1   network 10.1.1.0 0.0.0.3 area 1    redistribute connected subnets   

Before summarizing the routes, inspect the IP routing table on Router A to verify that the four networks are being advertised.

 rtrA#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets C       1.1.1.1 is directly connected, Loopback0      2.0.0.0/32 is subnetted, 1 subnets O E2    2.2.2.2 [110/20] via 10.1.1.2, 00:03:17, Serial0/1      156.26.0.0/28 is subnetted, 4 subnets  O E2    156.26.32.32 [110/20] via 10.1.1.2, 00:03:17, Serial0/1   O E2    156.26.32.48 [110/20] via 10.1.1.2, 00:03:17, Serial0/1   O E2    156.26.32.0 [110/20] via 10.1.1.2, 00:02:52, Serial0/1   O E2    156.26.32.16 [110/20] via 10.1.1.2, 00:03:17, Serial0/1  10.0.0.0/30 is subnetted, 1 subnets C       10.1.1.0 is directly connected, Serial0/1 

A 27-bit subnet mask will be used to summarize the four loopback addresses being advertised by Router B into two summaries. Modify the configuration on Router B in order to summarize the four loopback addresses into two summaries.

 Router B  router ospf 1    summary-address 156.26.32.0 255.255.255.224 tag 88     summary-address 156.26.32.32 255.255.255.224 tag 42    network 10.1.1.0 0.0.0.3 area 1  

Verification

Verify that Router B has summarized the four loopback networks into two summaries by inspecting the IP routing table on Router A.

 rtrA#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets C       1.1.1.1 is directly connected, Loopback0      2.0.0.0/32 is subnetted, 1 subnets O E2    2.2.2.2 [110/20] via 10.1.1.2, 00:36:53, Serial0/1      156.26.0.0/27 is subnetted, 2 subnets  O E2    156.26.32.32 [110/20] via 10.1.1.2, 00:01:04, Serial0/1   O E2    156.26.32.0 [110/20] via 10.1.1.2, 00:01:09, Serial0/1  10.0.0.0/30 is subnetted, 1 subnets C       10.1.1.0 is directly connected, Serial0/1 

Verify that the summaries have been tagged with the proper values.

 rtrA#  show ip route 156.26.32.0  Routing entry for 156.26.32.0/27   Known via "ospf 1", distance 110, metric 20  Tag 88, type extern 2, forward metric 64  Redistributing via ospf 1   Last update from 10.1.1.2 on Serial0/1, 00:02:43 ago   Routing Descriptor Blocks:   * 10.1.1.2, from 2.2.2.2, 00:02:43 ago, via Serial0/1       Route metric is 20, traffic share count is 1 rtrA#  show ip route 156.26.32.32  Routing entry for 156.26.32.32/27   Known via "ospf 1", distance 110, metric 20  Tag 42, type extern 2, forward metric 64  Redistributing via ospf 1   Last update from 10.1.1.2 on Serial0/1, 00:02:46 ago   Routing Descriptor Blocks:   * 10.1.1.2, from 2.2.2.2, 00:02:46 ago, via Serial0/1       Route metric is 20, traffic share count is 1 

Configuration Example 2: Using the Tag Value to Control Route Redistribution

In Figure 16-2, Routers A and C are running RIP Version 2. Redistribute OSPF into RIP on Router A, but allow only those routes with a tag value of 88 to be redistributed. Add the configuration for Router C and modify the configuration for Router A as follows :

 Router A  interface Serial0/0   ip address 10.1.1.9 255.255.255.252   !   interface Serial0/1   ip address 10.1.1.1 255.255.255.252   clockrate 64000   !   router ospf 1   network 10.1.1.0 0.0.0.3 area 1   !   router rip   version 2    redistribute ospf 1 metric 1 route-map checktags    passive-interface Serial0/1   network 10.0.0.0   no auto-summary   !    route-map checktags permit 10     match tag 88   _______________________________________________________________________ Router C  interface Serial1   ip address 10.1.1.10 255.255.255.252   clockrate 64000   !   router rip   version 2   network 10.0.0.0  

Verification

Verify that the only routes that were redistributed into RIP on Router A are routes with a tag value of 88.

 rtrC#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set  156.26.0.0/27 is subnetted, 1 subnets   R       156.26.32.0 [120/1] via 10.1.1.9, 00:00:25, Serial1  10.0.0.0/30 is subnetted, 2 subnets C       10.1.1.8 is directly connected, Serial1 R       10.1.1.0 [120/1] via 10.1.1.9, 00:00:25, Serial1 

Troubleshooting

Step 1. Verify that there is a neighbor relationship between the OSPF routers by using the show ip ospf neighbor command.

Step 2. The summary-address command will only work on an OSPF ASBR.

Step 3. Verify that you are using the correct IP address and mask with the summary-address command.