Ticket #10

Ticket #10

Network diagram

IGP diagram


The problem:

R6 was configured to summarize R3's Lo30,Lo31,Lo32 and Lo33, so R4 would see only one summarized route for them.

However, R4 still sees all the routes.

Fix the problem while, making sure R6 sees all R3's routes.

The solution:

First, lets check R4's routing table.

On R4:

R4#sh ip route

Codes: C - connected, S - static, 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

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route


Gateway of last resort is not set


     1.0.0.0/8 is variably subnetted, 5 subnets, 2 masks

O       1.15.6.6/32 [110/2] via 1.15.46.6, 00:32:43, FastEthernet0/1

C       1.15.4.4/32 is directly connected, Loopback0

O IA    1.15.3.3/32 [110/3] via 1.15.46.6, 00:32:43, FastEthernet0/1

C       1.15.46.0/24 is directly connected, FastEthernet0/1

O IA    1.15.36.0/24 [110/2] via 1.15.46.6, 00:32:43, FastEthernet0/1

     3.0.0.0/32 is subnetted, 4 subnets

O E2    3.3.3.3 [110/20] via 1.15.46.6, 00:31:26, FastEthernet0/1

O E2    3.3.3.2 [110/20] via 1.15.46.6, 00:31:26, FastEthernet0/1

O E2    3.3.3.1 [110/20] via 1.15.46.6, 00:31:26, FastEthernet0/1

O E2    3.3.3.0 [110/20] via 1.15.46.6, 00:31:26, FastEthernet0/1


Indeed, we can see that R4 do not see a summarized route for R3's Loopback interfaces, but sp

Lets check R6's OSPF configuration to check how it was configured to summarize the routes.

On R6:

R6#sh run | sec router ospf

router ospf 1

 log-adjacency-changes

 summary-address 3.3.3.0 255.255.255.252


R6 was configured to summaraize R3's Lo interfaces, but it is not working? Why?

The reason is that in OSPF, only the originating router can summarize external LSAs, and since R3 is originating the routes, only R3 can summarize them.

Since we are asked that R6 will have specific routes for R3's Loopbacks, we need R6 to do the summarization.

In order for R6 to summarize OSPF routes, we need to cause R6 to generate these routes it self!

One of the options to do so, is to turn area 1 to NSSA. Then R6 will translate LSA type 7 comming from R3 to LSA type 5 going to R4. And then we can do summarization.

On R3:

R3(config)#router ospf 1

R3(config-router)#area 1 nssa

On R6:

R6(config)#router ospf 1

R6(config-router)#area 1 nssa


Now, lets check R4's routing table.

On R4:

R4#sh ip route

Codes: C - connected, S - static, 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

       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

       ia - IS-IS inter area, * - candidate default, U - per-user static route

       o - ODR, P - periodic downloaded static route


Gateway of last resort is not set


     1.0.0.0/8 is variably subnetted, 5 subnets, 2 masks

O       1.15.6.6/32 [110/2] via 1.15.46.6, 01:32:25, FastEthernet0/1

C       1.15.4.4/32 is directly connected, Loopback0

O IA    1.15.3.3/32 [110/3] via 1.15.46.6, 00:00:29, FastEthernet0/1

C       1.15.46.0/24 is directly connected, FastEthernet0/1

O IA    1.15.36.0/24 [110/2] via 1.15.46.6, 01:32:25, FastEthernet0/1

     3.0.0.0/30 is subnetted, 1 subnets

O E2    3.3.3.0 [110/20] via 1.15.46.6, 00:00:24, FastEthernet0/1


Success!! Now the routes for R3's Loopback interfaces are being summarized.
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