CCNP / BSCI Examination Tutorial: Route Summarization And The OSPF Null Interface
CCNP Test good results, especially over the BSCI Examination, demands you have an understanding of the small print of route summarization. This talent not just involves that you've a comfort and ease stage with binary conversions, but You need to know the way and exactly where to use route summarization with Every unique protocol.
You also have to know the “Negative effects” of route summarization. With OSPF, there will basically be an additional interface produced at The purpose of summarization, which catches loads of CCNP candidates by surprise. Let’s Consider the null0 interface and how it pertains to OSPF summarization.
On R1, the subsequent networks are redistributed into OSPF, then summarized.
interface Loopback16
ip deal with sixteen.16.sixteen.16 255.0.0.0
interface Loopback17
ip deal with seventeen.seventeen.17.17 먹튀 255.0.0.0
interface Loopback18
ip tackle 18.18.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 connected subnets
R1(config-router)#summary-handle sixteen.0.0.0 252.0.0.0
The summary handle appears on R2, a downstream router.
R2#exhibit ip route ospf
O E2 16.0.0.0/6 [a hundred and ten/twenty] via 172.twelve.123.1, 00:00:05, Serial0
Allow’s return to R1 and take a look at its OSPF table.
R1#exhibit ip route ospf
O 16.0.0.0/six is a summary, 00:01:fifty one, Null0
The place did the null0 interface originate from, and why could it be there? Packets despatched on the null interface are dropped, and In cases like this, that’s a superb point.
Whenever you configure summary routes in OSPF, a route to null0 might be set up into the OSPF routing desk. This helps to forestall routing loops. Any packets destined for your routes that have been summarized may have an extended match from the routing table, as demonstrated below…
C seventeen.0.0.0/eight is specifically related, Loopback17
C 16.0.0.0/eight is immediately linked, Loopback16
C 19.0.0.0/eight is immediately connected, Loopback19
C 18.0.0.0/8 is straight connected, Loopback18
O sixteen.0.0.0/six is really a summary, 00:01:fifty one, Null0
.. and packets that don't match on the list of summarized routes but do match the summary route will probably be dropped.
Avoiding routing loops when performing route redistribution and summarization is vital. OSPF offers us just a little help in that regard in this example, and while you analyze more elaborate redistribution scenarios on your technique to the CCNP and CCIE, you’ll recognize that we’ll just take all the help we could get!