CCNP / BSCI Examination Tutorial: Route Summarization As well as the OSPF Null Interface
CCNP exam success, particularly on the BSCI Examination, demands you have an understanding of the details of route summarization. This ability not simply needs that you've got a consolation stage with binary conversions, but You must know the way and wherever to use route summarization with Just about every personal protocol.
You also have to know the “Unwanted effects” of route summarization. With OSPF, there will actually be an extra interface established at the point of summarization, and this catches a great deal of CCNP candidates unexpectedly. Let’s Have a look at the null0 interface And just how it relates to OSPF summarization.
On R1, the next networks are redistributed into OSPF, and after that summarized.
interface Loopback16
ip handle sixteen.sixteen.sixteen.sixteen 255.0.0.0
interface Loopback17
ip deal with 17.17.seventeen.17 255.0.0.0
interface Loopback18
ip handle 18.eighteen.eighteen.eighteen 255.0.0.0
interface Loopback19
ip deal with 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute connected subnets
R1(config-router)#summary-handle 16.0.0.0 252.0.0.0
The summary tackle seems on R2, a downstream router.
R2#present ip route ospf
O E2 16.0.0.0/six [a hundred and ten/twenty] by way of 172.12.123.1, 00:00:05, Serial0
Let’s go back to R1 and look at its OSPF desk.
R1#clearly show ip route ospf
O 16.0.0.0/six can be a summary, 00:01:51, Null0
Wherever did the null0 interface come from, and why is it there? Packets despatched into the null interface are dropped, and in this case, that’s a very good issue.
After you configure summary routes in OSPF, a path to null0 might be set up in to the OSPF routing desk. This helps to avoid routing loops. Any packets destined with the routes which were summarized will likely have a longer match from the routing table, as revealed down below…
C seventeen.0.0.0/eight is specifically linked, Loopback17
C 16.0.0.0/eight is instantly linked, Loopback16
C 19.0.0.0/eight is instantly connected, Loopback19
C 18.0.0.0/eight is immediately linked, Loopback18
O 16.0.0.0/six is really a summary, 00:01:51, Null0
.. and packets that don't match one of several summarized routes but do match the summary route might 토토사이트 be dropped.
Blocking routing loops when doing route redistribution and summarization is significant. OSPF gives us a little bit help in that regard in this situation, and as you review much more sophisticated redistribution scenarios on your way to the CCNP and CCIE, you’ll realize that we’ll get all the help we can get!