CCNP / BSCI Exam Tutorial: Route Summarization As well as the OSPF Null Interface
CCNP exam achievement, particularly on the BSCI Test, needs you fully grasp the details of route summarization. This talent not just involves that you've a comfort degree with binary conversions, but You must understand how and exactly where to use route summarization with Every unique protocol.
You also have to be aware of the “Unwanted side effects” of route summarization. With OSPF, there'll truly be an extra interface developed at the point of summarization, and this catches plenty of CCNP candidates by surprise. Permit’s Examine the null0 interface And the way it pertains to OSPF summarization.
On R1, the following networks are redistributed into OSPF, and then summarized.
interface Loopback16
ip handle 16.sixteen.16.16 255.0.0.0
interface Loopback17
ip deal with 17.17.17.17 255.0.0.0
interface Loopback18
ip deal with eighteen.eighteen.eighteen.eighteen 255.0.0.0
interface Loopback19
ip address 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute related subnets
R1(config-router)#summary-deal with sixteen.0.0.0 252.0.0.0
The summary deal with 먹튀검증 seems on R2, a downstream router.
R2#demonstrate ip route ospf
O E2 sixteen.0.0.0/six [110/20] by way of 172.12.123.one, 00:00:05, Serial0
Enable’s return to R1 and examine its OSPF desk.
R1#demonstrate ip route ospf
O 16.0.0.0/6 is often a summary, 00:01:51, Null0
Exactly where did the null0 interface originate from, and why could it be there? Packets sent towards the null interface are dropped, and in this case, that’s a great point.
Any time you configure summary routes in OSPF, a route to null0 is going to be set up in to the OSPF routing table. This helps to forestall routing loops. Any packets destined for the routes which were summarized will have a longer match in the routing table, as shown below…
C seventeen.0.0.0/8 is specifically linked, Loopback17
C 16.0.0.0/8 is straight related, Loopback16
C 19.0.0.0/eight is right connected, Loopback19
C 18.0.0.0/eight is immediately connected, Loopback18
O sixteen.0.0.0/6 can be a summary, 00:01:fifty one, Null0
.. and packets that don't match one of several summarized routes but do match the summary route will likely be dropped.
Avoiding routing loops when carrying out route redistribution and summarization is vital. OSPF presents us just a little assist in that regard in this case, and while you examine more intricate redistribution situations on your own way to the CCNP and CCIE, you’ll understand that we’ll just take all the help we could possibly get!