CCNP / BSCI Examination Tutorial: Route Summarization And also the OSPF Null Interface
CCNP Examination results, particularly within the BSCI exam, needs you recognize the main points of route summarization. This talent not only involves you have a comfort level with binary conversions, but You need to know how and the place to apply route summarization with Each and every individual protocol.
You even have to be aware of the “Uncomfortable side effects” of route summarization. With OSPF, there'll essentially be an extra interface created at the point of summarization, and this catches loads of CCNP candidates by surprise. Enable’s Consider the null0 interface And the way it pertains to OSPF summarization.
On R1, the next networks are redistributed into OSPF, and afterwards summarized.
interface Loopback16
ip handle 16.16.sixteen.sixteen 255.0.0.0
interface Loopback17
ip tackle 17.seventeen.seventeen.seventeen 255.0.0.0
interface Loopback18
ip address 18.eighteen.18.eighteen 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-tackle sixteen.0.0.0 252.0.0.0
The summary deal with seems on R2, a downstream router.
R2#exhibit ip route ospf
O E2 16.0.0.0/6 [one hundred ten/twenty] by using 172.12.123.1, 00:00:05, Serial0
Permit’s go back to R1 and evaluate its OSPF desk.
R1#exhibit ip route ospf
O sixteen.0.0.0/6 is actually a summary, 00:01:fifty one, Null0
Exactly where did the null0 interface come from, and why is it there? Packets despatched on the null 토토 interface are dropped, and In such a case, that’s a good factor.
After you configure summary routes in OSPF, a route to null0 will probably be put in into your OSPF routing table. This aids to stop routing loops. Any packets destined for the routes which were summarized will have a longer match inside the routing desk, as proven underneath…
C seventeen.0.0.0/8 is specifically connected, Loopback17
C 16.0.0.0/8 is instantly linked, Loopback16
C 19.0.0.0/eight is specifically linked, Loopback19
C eighteen.0.0.0/8 is instantly connected, Loopback18
O sixteen.0.0.0/6 is actually a summary, 00:01:fifty one, Null0
.. and packets that don't match among the list of summarized routes but do match the summary route will likely be dropped.
Protecting against routing loops when carrying out route redistribution and summarization is important. OSPF provides us slightly help in that regard in this example, and as you research far more complex redistribution scenarios on the method to the CCNP and CCIE, you’ll know that we’ll choose all the assistance we might get!