Summarization challenge (thinking outside the box - solution2)

This exercise was first post by Arwin Reprakash (http://ithitman.blogspot.com/2015/03/configuring-ospf-summarization-lab.html#more). I just implement the solution that he proposed

 

 

THE PROBLEM

 

Summarize 192.168.1.2/32 from Area 2 as 192.168.1.0/24 into area 0.

 

RESTRICTIONS

 

Do not use area-range command or summary-address to summarize the routes into Area 0.

R3 and other routers in Area 0 or any new additional areas should only have the summary address to reach 192.168.1.2. 

If prefix 192.168.1.2/32 is withdrawn (i.e shutdown loopback0 on R2) from R1 OSPF database then 192.168.1.0/24 should not be summarized/advertised into area 0.

 

 

THE SOLUTION

 

First let's stop advertising 192.168.1.2 into área 0. This must be done in the ABR (R1), it has no effect if you apply the following command in R2. Check cisco documentation for more details (http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fiarospf.html)

 

R1#conf term

R1(config)#router ospf 1
R1(config-router)#area 2 filter-list prefix NOADVERTISE out

 

 

A prefix-list filter will be applied to the routes advertise by área 2. let's configure the prefix-filter:

 

R1(config)#ip prefix-list NOADVERTISE deny 192.168.1.2/32


If we check R3 routing table will see that there is no route for 192.168.1.2

The next step is to créate an SLA to check for interface l0 status by ping


R2#show run | section sla
ip sla 1
 icmp-echo 192.168.1.2
 frequency 5
ip sla schedule 1 life forever start-time now


We'll associate that SLA with a TRACK to check the  SLA status

R2(config)#track 1 ip sla 1 reachability
Now let's add a static route for 192.168.1.2 which will remain in R2's routing table as long as the TRACK for the SLA is ok

R2(config)#ip route 192.168.1.0 255.255.255.0 GigabitEthernet0/1 track 1


Finally we redistribute that static route into ospf

R2#show run | section ospf
 ip ospf cost 1
router ospf 1
 redistribute static subnets
 network 12.12.12.0 0.0.0.255 area 2
 network 192.168.1.2 0.0.0.0 area 2

If we check R3's routing table we'll see the route for 192.168.1.0/24

R3#show ip route ospf
O E2  192.168.1.0/24 [110/20] via 13.13.13.1, 00:52:37, GigabitEthernet0/1


To verify let's make a ping from R3 to 192.168.1.2

R3#ping 192.168.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds:
!!!!!


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