CCNP / BSCI Exam Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP exam accomplishment, especially around the BSCI Examination, calls for you comprehend the small print of route summarization. This ability not just involves you have a ease and comfort amount with binary conversions, but You will need to understand how and the place to use route summarization with Every single specific protocol.
You also have to know the “Unwanted side effects” of route summarization. With OSPF, there'll really be an additional interface made at The purpose of summarization, and this catches a great deal of CCNP candidates by surprise. Enable’s Examine the null0 interface And the way it relates to OSPF summarization.
On R1, the following networks are redistributed into OSPF, and afterwards summarized.
interface Loopback16
ip handle 16.sixteen.16.16 255.0.0.0
interface Loopback17
ip address seventeen.seventeen.seventeen.seventeen 255.0.0.0
interface Loopback18
ip deal with 18.18.18.18 255.0.0.0
interface Loopback19
ip tackle 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute linked subnets
R1(config-router)#summary-address 16.0.0.0 252.0.0.0
The summary tackle seems on R2, a downstream router.
R2#demonstrate ip route ospf
O E2 16.0.0.0/six [one hundred ten/twenty] by way of 172.twelve.123.1, 토토 00:00:05, Serial0
Enable’s return to R1 and take a look at its OSPF desk.
R1#demonstrate ip route ospf
O 16.0.0.0/6 is a summary, 00:01:51, Null0
Where by did the null0 interface come from, and why can it be there? Packets despatched for the null interface are dropped, and In this instance, that’s a superb matter.
If you configure summary routes in OSPF, a route to null0 will probably be set up into your OSPF routing desk. This allows to prevent routing loops. Any packets destined with the routes that were summarized could have an extended match while in the routing table, as proven down below…
C seventeen.0.0.0/eight is immediately related, Loopback17
C 16.0.0.0/8 is right linked, Loopback16
C 19.0.0.0/8 is directly connected, Loopback19
C eighteen.0.0.0/eight is immediately connected, Loopback18
O sixteen.0.0.0/six is often a summary, 00:01:51, Null0
.. and packets that do not match one of many summarized routes but do match the summary route might be dropped.
Blocking routing loops when performing route redistribution and summarization is important. OSPF offers us somewhat assist in that regard in this case, and as you review additional complex redistribution eventualities on your technique to the CCNP and CCIE, you’ll know that we’ll acquire all the help we can get!