CCNP / BSCI Exam Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP Test achievement, specially around the BSCI exam, demands you realize the small print of route summarization. This ability not simply calls for that you've got a ease and comfort degree with binary conversions, but You will need to understand how and where by to apply route summarization with Every single individual protocol.
You even have to know the “Unwanted side effects” of route summarization. With OSPF, there'll basically be an extra interface created at The purpose of summarization, and this catches loads of CCNP candidates without warning. Enable’s Look into the null0 interface and how it relates to OSPF summarization.
On R1, the next networks are redistributed into OSPF, after which summarized.
interface Loopback16
ip address sixteen.16.16.sixteen 255.0.0.0
interface Loopback17
ip handle 17.17.seventeen.17 255.0.0.0
interface Loopback18
ip handle eighteen.eighteen.eighteen.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 related subnets
R1(config-router)#summary-handle 16.0.0.0 252.0.0.0
The summary address appears on R2, a downstream router.
R2#exhibit ip route ospf
O E2 16.0.0.0/six [110/twenty] via 172.twelve.123.1, 00:00:05, Serial0
Let’s go back to R1 and look at its OSPF table.
R1#exhibit ip route ospf
O 16.0.0.0/6 is usually a summary, 00:01:fifty one, Null0
Exactly where did the null0 interface originate from, and why could it be 토토 there? Packets sent towards the null interface are dropped, and In this instance, that’s a very good issue.
When you configure summary routes in OSPF, a path to null0 might be put in into the OSPF routing table. This aids to stop routing loops. Any packets destined with the routes that have been summarized will have an extended match from the routing table, as proven under…
C seventeen.0.0.0/8 is specifically related, Loopback17
C sixteen.0.0.0/8 is right related, Loopback16
C 19.0.0.0/8 is straight linked, Loopback19
C 18.0.0.0/eight is instantly linked, Loopback18
O sixteen.0.0.0/six can be 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.
Blocking routing loops when undertaking route redistribution and summarization is significant. OSPF presents us a little bit help in that regard in this situation, and as you study extra intricate redistribution eventualities on your own method to the CCNP and CCIE, you’ll recognize that we’ll consider all the help we can get!