CCNP / BSCI Exam Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP Examination accomplishment, specifically within the BSCI Examination, calls for you understand the small print of route summarization. This talent not only demands you have a convenience stage with binary conversions, but you have to know the way and the place to apply route summarization with Just about every personal protocol.
You also have to learn the “side effects” of route summarization. With OSPF, there will basically be an additional interface established at The purpose of summarization, which catches many CCNP candidates by surprise. Enable’s Look into the null0 interface And just how it pertains to OSPF summarization.
On R1, the subsequent networks are redistributed into OSPF, after which summarized.
interface Loopback16
ip deal with 16.16.sixteen.16 255.0.0.0
interface Loopback17
ip tackle 17.17.17.17 255.0.0.0
interface Loopback18
ip tackle eighteen.18.18.eighteen 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-handle sixteen.0.0.0 252.0.0.0
The summary address appears on R2, a downstream router.
R2#demonstrate ip route ospf
O E2 sixteen.0.0.0/6 [one hundred ten/twenty] via 172.12.123.1, 00:00:05, Serial0
Permit’s return to R1 and look at its OSPF table.
R1#show ip route ospf
O sixteen.0.0.0/6 can be a summary, 00:01:fifty one, Null0
Where by did the null0 interface originate from, and why is it there? Packets despatched on the null interface are dropped, and In cases like this, that’s a fantastic issue.
Whenever you configure summary routes in OSPF, a route to null0 will probably be installed into the OSPF routing desk. This aids to stop routing loops. Any packets destined for the routes which were summarized will likely have a longer match while in the routing desk, as shown underneath…
C seventeen.0.0.0/8 is right related, Loopback17
C sixteen.0.0.0/8 is right connected, Loopback16
C 19.0.0.0/eight is specifically related, Loopback19
C eighteen.0.0.0/eight is immediately related, Loopback18
O 16.0.0.0/six 토토 is usually a summary, 00:01:fifty one, Null0
.. and packets that don't match among the summarized routes but do match the summary route will be dropped.
Protecting against routing loops when carrying out route redistribution and summarization is significant. OSPF gives us a little bit help in that regard in this example, and as you research a lot more intricate redistribution situations on your method to the CCNP and CCIE, you’ll know that we’ll acquire all the assistance we will get!