CCNP / BSCI Examination Tutorial: Route Summarization Along with the OSPF Null Interface
CCNP Test accomplishment, specially over the BSCI Examination, requires you understand the main points of route summarization. This ability not merely demands that you've got a comfort amount with binary conversions, but You need to understand how and wherever to use route summarization with Each and every unique protocol.
You even have to find out the “side effects” of route summarization. With OSPF, there'll truly be an additional interface created at the point of summarization, and this catches loads of CCNP candidates without warning. Let’s Examine the null0 interface And the way it relates to OSPF summarization.
On R1, the subsequent networks are redistributed into OSPF, and afterwards summarized.
interface Loopback16
ip address 16.sixteen.16.16 255.0.0.0
interface Loopback17
ip tackle 17.seventeen.17.17 255.0.0.0
interface Loopback18
ip deal with 18.18.18.eighteen 255.0.0.0
interface Loopback19
ip address 19.19.19.19 255.0.0.0
R1(config)#router ospf one
R1(config-router)#redistribute related subnets
R1(config-router)#summary-deal with 16.0.0.0 252.0.0.0
The summary address appears on R2, a downstream router.
R2#demonstrate ip route ospf
O E2 sixteen.0.0.0/six [one hundred ten/twenty] via 172.12.123.one, 00:00:05, Serial0
Permit’s return to R1 and take a look at its OSPF desk.
R1#demonstrate ip route ospf
O sixteen.0.0.0/six is usually a summary, 00:01:fifty one, Null0
Where did the null0 interface originate from, and why can it be there? Packets sent into the null interface are dropped, and In such cases, that’s a very good factor.
Any time you configure summary routes in OSPF, a path to null0 will be installed in the OSPF routing desk. This will help to avoid routing loops. Any packets destined for that routes which were summarized will likely have a longer match during the routing desk, as proven underneath…
C 17.0.0.0/eight is specifically connected, Loopback17
C 16.0.0.0/eight is instantly connected, Loopback16
C 19.0.0.0/eight is straight connected, Loopback19
C 18.0.0.0/8 is directly related, Loopback18
O 16.0.0.0/six is really a summary, 00:01:fifty one, Null0
.. and packets that do not match one of the summarized routes but do match the summary route is going to be dropped.
Blocking routing loops when doing route redistribution and summarization is significant. OSPF gives us slightly help in that regard 먹튀 in this situation, and when you review more intricate redistribution eventualities on the method to the CCNP and CCIE, you’ll know that we’ll acquire all the assistance we could get!