As part of my study notes, this will be the last series of OSPF Prefix Summarization which I will be focusing on LSA TYPE 5 or what we also know as External Routes Summarizations.

OBJECTIVE:

1. To understand that Type 5 LSA prefixes can only be summarized on ABR or ASBR.

2. To used  “redistributed connected subnets”  on ASBR to emulate routes from other routing domains.

3.  To summarized prefixes using the command “summary address” under OSPF process.

4. To show that any link failures on a summarized prefix will not affect the existing LSDB.

5. To check connectivity is working between SINGAPORE and MANILA router’s loopback addresses.

Here is my topology for this laboratory,

 

  Here are my configurations for the routers:

Now, let’s check the OSPF adjacencies,

 

So what does the LSDB on the router’s tells us so far, as we have not done the summarization on the ASBR yet.

 

>> Again as seen above, we can conclude that the 4 prefixes for the 10.x.x.x network were sent as LSU by MANILA router to the Melbourne & Singapore. We can see the Type-5 AS External LSA with the corresponding Link ID’s and from which router it came from ( in this case advertisement were all from 10.10.13.1 or the MA N ILA router)

 

 >> Similarly , we can see the same TYPE-5 LSA’s from MELBOURNE and MANILA router.

>> So as we can see, we are still NOT doing the summarizations as observed from LSDB’s on the routers. We should the fact that we can the same 4 prefixes for the 10.x.x.x network on the routing table entries.

So let’s start summarizing the 4 prefixes on the MANILA Router. Remember that we can used the

“summary address”command under OSPGF process to accomplish this. I will be summarizing the 4 prefixes into 10.0.0.0/8.

VERIFICATIONS:

A. Let’s check the LSDB of the routers by this time that we have enable the summarizations on MANILA router.

 

>>> As seen above, I have the LINK ID of 10.0.0.0 which is being advertised by MANILA router (10.10.13.1). The Router ID of 10.10.13.1 will be the highest loopbacK interface on the router not unless we have manually set this up under OSPF process.

 

>>>  Previously, we have 4 prefixes in LSDB of MANILA router for the 10.x.x.x subnets but now, we can only see just 1 summarized prefix.

 

>>> What about MELBOURNE & SINGAPORE router,

>>> As observed from both MELBOURNE & SINGAPORE routers, MANILA router have sent the LSU’s for the new LSA containing the summarized prefix with the LINK ID of 10.0.0.0.

B. So what’s the routing table tells us about this summarized prefix,

 

>>> As observed, we only have a single summarized prefix received by MELBOURNE router as we have manually summarized from MANILA router the 4 prefixes to a single prefix of 10.0.0.0/8. We can see it as O E2. If you still remember, This OSPF codes refers to OSPF External Routes or Routes that were redistributed into OSPF.  I should be able to see the same results from SINGAPORE router as seen below,

 

 

Let’s try a bit of some failure scenarios here, I will disabled the Loopback Interface 0 & 1 on MANILA router and let’s check whether there will be a changes on the LSDB sequence numbers on both MELBOURNE and SINGAPORE routers for the 10.0.0.0 Link ID.

Now, let’s check the LSDB of MELBOURNE and SINGAPORE routers,

 

 

>>> As seen there were no changes on the SEQUENCE Number of both MELBOURNE & SINGAPORE router as compared with the previous LSDB records even though, I have manually shutdown Loopback 0 & Loopback 1.

 

>>> As we know, the sequence number will increase if there are changes on existing networks. We can proved by simply adding a new network in MANILA and advertise it into OSPF.

 

My current configurations in MANILA will redistribute all “Connected Network”. So let’s check the LSDB updates on MELBOURNE & SINGAPORE. As we see below, once we add a new network of 100.100.100.0/24 , the sequence number for the Link ID 10.0.0.0 have incremented by 1.

That’s enough for proving how LSDB is being updated.

 

C. Let’s test the connectivity.

 

 A successful ping sourcing SINGAPORE loopback towards any of MANILA loopback interface will proved our connectivity will be successful and we have setup the correct configurations.