CCNP / BSCI Examination Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP Test accomplishment, specifically around the BSCI Examination, needs you understand the small print of route summarization. This talent not only needs that you have a ease and comfort amount with binary conversions, but You need to understand how and the place to use route summarization with each unique protocol.
You also have to learn the “Unwanted side effects” of route summarization. With OSPF, there'll essentially be an additional interface created at The purpose of summarization, and this catches loads of CCNP candidates abruptly. Permit’s Look into the null0 interface And the way it pertains to OSPF summarization.
On R1, the following networks are redistributed into OSPF, after which summarized.
interface Loopback16
ip address sixteen.sixteen.sixteen.sixteen 255.0.0.0
interface Loopback17
ip address 17.seventeen.17.17 255.0.0.0
interface Loopback18
ip tackle eighteen.eighteen.18.18 255.0.0.0
interface Loopback19
ip tackle 19.19.19.19 255.0.0.0
R1(config)#router ospf one
R1(config-router)#redistribute linked subnets
R1(config-router)#summary-deal with 16.0.0.0 252.0.0.0
The summary tackle appears on R2, a downstream router.
R2#show ip route ospf
O E2 16.0.0.0/6 [110/twenty] by way of 172.twelve.123.1, 00:00:05, Serial0
Enable’s return to R1 and look at its 토토사이트 OSPF desk.
R1#present ip route ospf
O 16.0.0.0/6 is really a summary, 00:01:fifty one, Null0
In which did the null0 interface originate from, and why is it there? Packets despatched for the null interface are dropped, and In cases like this, that’s a good issue.
Any time you configure summary routes in OSPF, a path to null0 will be mounted into your OSPF routing desk. This can help to circumvent routing loops. Any packets destined for that routes which were summarized should have a longer match from the routing table, as shown below…
C seventeen.0.0.0/8 is specifically linked, Loopback17
C sixteen.0.0.0/eight is instantly linked, Loopback16
C 19.0.0.0/8 is instantly related, Loopback19
C 18.0.0.0/8 is instantly related, Loopback18
O sixteen.0.0.0/6 can be a summary, 00:01:51, Null0
.. and packets that do not match one of several summarized routes but do match the summary route will likely be dropped.
Blocking routing loops when executing route redistribution and summarization is vital. OSPF presents us slightly assist in that regard in this situation, and when you analyze much more advanced redistribution eventualities on your own way to the CCNP and CCIE, you’ll recognize that we’ll get all the assistance we will get!