CCNP / BSCI Examination Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP exam good results, especially within the BSCI exam, demands you comprehend the details of route summarization. This skill not only calls for you have a comfort and ease stage with binary conversions, but You need to understand how and exactly where to use route summarization with Each and every person protocol.
You also have to know the “Uncomfortable side effects” of route summarization. With OSPF, there will actually be an additional interface produced at the point of summarization, and this catches many CCNP candidates by surprise. Allow’s take a look at the null0 interface And the way it pertains to OSPF summarization.
On R1, the subsequent networks are redistributed into OSPF, after which you can summarized.
interface Loopback16
ip tackle 16.sixteen.sixteen.sixteen 255.0.0.0
interface Loopback17
ip tackle seventeen.seventeen.seventeen.17 255.0.0.0
interface 토토 Loopback18
ip deal with eighteen.eighteen.18.eighteen 255.0.0.0
interface Loopback19
ip tackle 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute connected subnets
R1(config-router)#summary-handle sixteen.0.0.0 252.0.0.0
The summary handle appears on R2, a downstream router.
R2#present ip route ospf
O E2 sixteen.0.0.0/six [110/20] via 172.12.123.one, 00:00:05, Serial0
Allow’s go back to R1 and examine its OSPF desk.
R1#demonstrate ip route ospf
O 16.0.0.0/six is actually a summary, 00:01:fifty one, Null0
Exactly where did the null0 interface come from, and why could it be there? Packets despatched into the null interface are dropped, and In such a case, that’s a fantastic factor.
If you configure summary routes in OSPF, a route to null0 is going to be put in into the OSPF routing desk. This assists to circumvent routing loops. Any packets destined for your routes that have been summarized could have an extended match inside the routing table, as demonstrated beneath…
C seventeen.0.0.0/eight is straight connected, Loopback17
C 16.0.0.0/eight is immediately related, Loopback16
C 19.0.0.0/eight is immediately related, Loopback19
C eighteen.0.0.0/8 is instantly linked, Loopback18
O 16.0.0.0/6 is a summary, 00:01:fifty one, Null0
.. and packets that don't match among the list of summarized routes but do match the summary route will be dropped.
Preventing routing loops when executing route redistribution and summarization is vital. OSPF offers us a bit help in that regard in this case, and while you examine extra sophisticated redistribution situations on your own way to the CCNP and CCIE, you’ll recognize that we’ll just take all the assistance we can get!