CCNP / BSCI Examination Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP exam accomplishment, particularly to the BSCI Test, calls for you fully grasp the details of route summarization. This skill not only calls for you have a comfort and ease amount with binary conversions, but You should understand how and in which to apply route summarization with Every single specific protocol.
You also have to grasp the “Unwanted side effects” of route summarization. With OSPF, there'll essentially be an additional interface made at The purpose of summarization, which catches a lot of CCNP candidates by surprise. Enable’s Consider the null0 interface And just how it pertains to OSPF summarization.
On R1, the next 먹튀 networks are redistributed into OSPF, and then summarized.
interface Loopback16
ip address sixteen.sixteen.16.sixteen 255.0.0.0
interface Loopback17
ip address 17.seventeen.17.seventeen 255.0.0.0
interface Loopback18
ip deal with 18.18.18.18 255.0.0.0
interface Loopback19
ip address 19.19.19.19 255.0.0.0
R1(config)#router ospf one
R1(config-router)#redistribute linked subnets
R1(config-router)#summary-deal with 16.0.0.0 252.0.0.0
The summary address seems on R2, a downstream router.
R2#show ip route ospf
O E2 sixteen.0.0.0/6 [one hundred ten/twenty] by using 172.twelve.123.one, 00:00:05, Serial0
Enable’s go back to R1 and examine its OSPF table.
R1#show ip route ospf
O 16.0.0.0/six is actually a summary, 00:01:fifty one, Null0
Wherever did the null0 interface come from, and why is it there? Packets sent to the null interface are dropped, and In this instance, that’s a superb issue.
Any time you configure summary routes in OSPF, a path to null0 might be mounted in to the OSPF routing table. This aids to circumvent routing loops. Any packets destined for your routes which were summarized should have an extended match within the routing table, as proven below…
C seventeen.0.0.0/eight is directly related, Loopback17
C sixteen.0.0.0/8 is right linked, Loopback16
C 19.0.0.0/8 is instantly linked, Loopback19
C 18.0.0.0/eight is right connected, Loopback18
O sixteen.0.0.0/six is often a summary, 00:01:51, Null0
.. and packets that don't match among the list of summarized routes but do match the summary route are going to be dropped.
Protecting against routing loops when performing route redistribution and summarization is significant. OSPF provides us a little bit assist in that regard in this example, and while you research far more intricate redistribution scenarios on your own approach to the CCNP and CCIE, you’ll realize that we’ll choose all the assistance we may get!