CCNP / BSCI Exam Tutorial: Route Summarization And The OSPF Null Interface
CCNP Test achievement, particularly around the BSCI Test, needs you understand the small print of route summarization. This talent not merely demands that you've a ease and comfort stage with binary conversions, but You should know the way and the place to apply route summarization with Every individual protocol.
You also have to be aware of the “Unwanted effects” of route summarization. With OSPF, there'll actually be an extra interface created at the point of summarization, and this catches a lot of CCNP candidates by surprise. Let’s Have a look at the null0 interface and how it pertains to OSPF summarization.
On R1, the subsequent networks are redistributed into OSPF, after which you can summarized.
interface Loopback16
ip tackle sixteen.16.sixteen.sixteen 255.0.0.0
interface Loopback17
ip handle seventeen.seventeen.seventeen.seventeen 255.0.0.0
interface Loopback18
ip handle eighteen.18.eighteen.eighteen 255.0.0.0
interface Loopback19
ip handle 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute linked subnets
R1(config-router)#summary-address sixteen.0.0.0 252.0.0.0
The summary deal with appears on R2, a downstream router.
R2#demonstrate ip route ospf
O E2 16.0.0.0/six [one hundred ten/twenty] by way of 172.12.123.one, 00:00:05, Serial0
Let’s go back to R1 and evaluate its OSPF desk.
R1#show ip route ospf
O sixteen.0.0.0/6 is actually a summary, 00:01:fifty one, Null0
Where by did the null0 interface originate from, and why can it be there? Packets sent on the null interface are dropped, and In this 먹튀 instance, that’s a fantastic thing.
If you configure summary routes in OSPF, a route to null0 will likely be set up to the OSPF routing desk. This assists to avoid routing loops. Any packets destined for your routes that were summarized will likely have an extended match in the routing table, as proven down below…
C seventeen.0.0.0/eight is specifically related, Loopback17
C 16.0.0.0/8 is instantly linked, Loopback16
C 19.0.0.0/eight is specifically connected, Loopback19
C eighteen.0.0.0/eight is directly connected, Loopback18
O 16.0.0.0/six can be a summary, 00:01:51, Null0
.. and packets that don't match one of several summarized routes but do match the summary route is going to be dropped.
Protecting against routing loops when doing route redistribution and summarization is important. OSPF provides us a little bit assist in that regard in this case, and while you review extra intricate redistribution eventualities in your solution to the CCNP and CCIE, you’ll recognize that we’ll choose all the assistance we can get!