CCNP / BSCI Exam Tutorial: Route Summarization And The OSPF Null Interface
CCNP Examination success, particularly over the BSCI exam, needs you have an understanding of the details of route summarization. This ability don't just calls for that you've got a ease and comfort stage with binary conversions, but You will need to understand how and exactly where to apply route summarization with each personal protocol.
You also have to understand the “Unintended effects” of route summarization. With OSPF, there'll truly be an extra interface created at the point of summarization, which catches a great deal of CCNP candidates by surprise. Permit’s Look into the null0 interface and how it relates to OSPF summarization.
On R1, the following networks are redistributed into OSPF, after which summarized.
interface Loopback16
ip tackle sixteen.sixteen.16.sixteen 255.0.0.0
interface Loopback17
ip handle seventeen.seventeen.seventeen.seventeen 255.0.0.0
interface Loopback18
ip deal with 18.eighteen.18.18 255.0.0.0
interface Loopback19
ip tackle 19.19.19.19 255.0.0.0
R1(config)#router ospf one
R1(config-router)#redistribute related subnets
R1(config-router)#summary-address 16.0.0.0 252.0.0.0
The summary address appears on R2, a downstream router.
R2#exhibit ip route ospf
O E2 16.0.0.0/six [one hundred ten/twenty] by using 172.12.123.1, 00:00:05, Serial0
Let’s go back to R1 and examine its OSPF desk.
R1#exhibit ip route ospf
O sixteen.0.0.0/6 is really a summary, 00:01:fifty one, Null0
In which did 먹튀 the null0 interface come from, and why is it there? Packets despatched towards the null interface are dropped, and In such cases, that’s a great matter.
Whenever you configure summary routes in OSPF, a path to null0 are going to be mounted in to the OSPF routing table. This helps to stop routing loops. Any packets destined for the routes that were summarized could have an extended match within the routing desk, as revealed down below…
C seventeen.0.0.0/eight is instantly related, Loopback17
C sixteen.0.0.0/eight is specifically linked, Loopback16
C 19.0.0.0/eight is straight related, Loopback19
C eighteen.0.0.0/8 is instantly linked, Loopback18
O sixteen.0.0.0/6 can be a summary, 00:01:fifty one, Null0
.. and packets that do not match among the summarized routes but do match the summary route will probably be dropped.
Blocking routing loops when carrying out route redistribution and summarization is vital. OSPF offers us somewhat assist in that regard in this case, and while you examine far more sophisticated redistribution scenarios on your own strategy to the CCNP and CCIE, you’ll know that we’ll get all the assistance we might get!