CCNP / BSCI Exam Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP Examination achievements, notably to the BSCI Test, requires you recognize the main points of route summarization. This talent not merely calls for that you have a comfort level with binary conversions, but It's important to know how and in which to use route summarization with each personal protocol.
You also have to grasp the “side effects” of route summarization. With OSPF, there'll actually be an additional interface designed at The purpose of summarization, which catches loads of CCNP candidates by surprise. Allow’s Look into the null0 interface and how it relates to OSPF summarization.
On R1, the next networks are redistributed into OSPF, then 먹튀검증 summarized.
interface Loopback16
ip tackle sixteen.sixteen.sixteen.sixteen 255.0.0.0
interface Loopback17
ip address seventeen.17.17.17 255.0.0.0
interface Loopback18
ip deal with 18.eighteen.18.eighteen 255.0.0.0
interface Loopback19
ip deal with 19.19.19.19 255.0.0.0
R1(config)#router ospf one
R1(config-router)#redistribute linked subnets
R1(config-router)#summary-handle sixteen.0.0.0 252.0.0.0
The summary tackle seems on R2, a downstream router.
R2#show ip route ospf
O E2 16.0.0.0/six [110/twenty] through 172.12.123.one, 00:00:05, Serial0
Let’s return to R1 and look at its OSPF table.
R1#demonstrate ip route ospf
O sixteen.0.0.0/6 is usually a summary, 00:01:51, Null0
Wherever did the null0 interface come from, and why can it be there? Packets despatched for the null interface are dropped, and in this case, that’s an excellent detail.
Any time you configure summary routes in OSPF, a route to null0 will be mounted to the OSPF routing desk. This will help to circumvent routing loops. Any packets destined for the routes that were summarized could have an extended match from the routing table, as shown down below…
C seventeen.0.0.0/8 is specifically related, Loopback17
C 16.0.0.0/8 is straight connected, Loopback16
C 19.0.0.0/eight is immediately connected, Loopback19
C eighteen.0.0.0/eight is instantly linked, Loopback18
O sixteen.0.0.0/six is really a summary, 00:01:51, Null0
.. and packets that do not match on the list of summarized routes but do match the summary route is going to be dropped.
Protecting against routing loops when accomplishing route redistribution and summarization is important. OSPF offers us somewhat assist in that regard in this example, and as you examine a lot more complicated redistribution eventualities on the way to the CCNP and CCIE, you’ll understand that we’ll just take all the assistance we could get!