CCNP / BSCI Examination Tutorial: Route Summarization And The OSPF Null Interface
CCNP Test achievement, significantly on the BSCI Examination, demands you fully grasp the details of route summarization. This ability not only requires you have a comfort degree with binary conversions, but You will need to know how and in which to apply route summarization with Each individual person protocol.
You also have to know the “Unwanted side effects” of route summarization. With OSPF, there will truly be an additional interface created at The purpose of summarization, and this catches a lot of CCNP candidates unexpectedly. Permit’s Consider the null0 interface And exactly how it pertains to OSPF summarization.
On R1, the next networks are redistributed into OSPF, then summarized.
interface Loopback16
ip deal with sixteen.sixteen.sixteen.16 255.0.0.0
interface Loopback17
ip address 17.17.17.17 255.0.0.0
interface Loopback18
ip address 18.18.18.eighteen 255.0.0.0
interface Loopback19
ip handle 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute connected subnets
R1(config-router)#summary-handle sixteen.0.0.0 252.0.0.0
The summary handle seems on R2, a downstream router.
R2#clearly show ip route ospf
O E2 sixteen.0.0.0/6 [a hundred and ten/20] by means of 172.twelve.123.one, 00:00:05, Serial0
Let’s return to R1 and look at its OSPF desk.
R1#clearly 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 come from, and why is it there? Packets sent for the null interface are dropped, and In such a 먹튀검증 case, that’s a great factor.
When you configure summary routes in OSPF, a route to null0 is going to be mounted into your OSPF routing desk. This aids to forestall routing loops. Any packets destined for that routes that were summarized will likely have an extended match while in the routing desk, as proven under…
C 17.0.0.0/eight is specifically connected, Loopback17
C 16.0.0.0/8 is immediately linked, Loopback16
C 19.0.0.0/8 is straight related, Loopback19
C eighteen.0.0.0/eight is right 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 will be dropped.
Stopping routing loops when undertaking route redistribution and summarization is important. OSPF gives us a bit assist in that regard in this example, and as you study a lot more complex redistribution situations on the strategy to the CCNP and CCIE, you’ll understand that we’ll take all the assistance we can get!