CCNP / BSCI Exam Tutorial: Route Summarization And The OSPF Null Interface
CCNP Examination achievements, especially over the BSCI Test, calls for you fully grasp the small print of route summarization. This ability not only necessitates that you have a convenience amount with binary conversions, but you have to know how and where to use route summarization with Each individual individual protocol.
You even have to know the “Unwanted side effects” of route summarization. With OSPF, there'll basically be an extra interface developed at The purpose of summarization, and this catches many CCNP candidates by surprise. Enable’s Consider the null0 interface And exactly how it relates to OSPF summarization.
On R1, the following networks are redistributed into OSPF, and after that summarized.
interface Loopback16
ip handle 16.16.sixteen.16 255.0.0.0
interface Loopback17
ip address 17.17.17.17 255.0.0.0
interface Loopback18
ip tackle eighteen.18.18.18 255.0.0.0
interface Loopback19
ip address 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute linked subnets
R1(config-router)#summary-deal with sixteen.0.0.0 252.0.0.0
The summary deal with seems on R2, a downstream router.
R2#demonstrate ip route ospf
O E2 16.0.0.0/6 [one hundred ten/twenty] by using 172.12.123.1, 00:00:05, Serial0
Allow’s return to R1 and look at its OSPF desk.
R1#display ip route ospf
O sixteen.0.0.0/six is actually a summary, 00:01:51, Null0
Where by did the null0 interface come from, and why can it be there? Packets despatched into the null interface are dropped, and In such cases, that’s a good thing.
Whenever you configure summary routes in OSPF, a path to null0 might be mounted to the OSPF routing desk. This aids to circumvent routing loops. Any packets destined with the routes which have been summarized should have an extended match in the routing table, as shown down below…
C 17.0.0.0/eight is specifically linked, Loopback17
C 16.0.0.0/8 is specifically linked, Loopback16
C 19.0.0.0/eight is straight linked, Loopback19
C eighteen.0.0.0/eight is directly linked, Loopback18
O sixteen.0.0.0/6 is really a summary, 00:01:fifty one, Null0
.. and packets that do not match among the summarized routes but do match the summary route will likely be dropped.
Preventing routing loops when performing route redistribution and summarization is important. OSPF gives us just a little help in that regard in this case, and when you research additional complex redistribution eventualities on your own way to the CCNP and CCIE, you’ll 토토사이트 know that we’ll just take all the assistance we can get!