CCNP / BSCI Test Tutorial: Route Summarization And also the OSPF Null Interface
CCNP Examination achievement, significantly on the BSCI exam, requires you have an understanding of the small print of route summarization. This ability not just demands you have a convenience amount with binary conversions, but You must know the way and wherever to apply route summarization with Just about every personal protocol.
You even have to learn the “Unintended effects” of route summarization. With OSPF, there will basically be an extra interface designed at the point of summarization, and this catches plenty of CCNP candidates by surprise. Let’s take a look at the null0 interface And the way it pertains to OSPF summarization.
On R1, the subsequent networks are redistributed into OSPF, then summarized.
interface Loopback16
ip tackle sixteen.sixteen.sixteen.16 255.0.0.0
interface Loopback17
ip address 17.seventeen.seventeen.seventeen 255.0.0.0
interface Loopback18
ip tackle eighteen.eighteen.18.eighteen 255.0.0.0
interface Loopback19
ip address 19.19.19.19 255.0.0.0
R1(config)#router ospf 1
R1(config-router)#redistribute connected subnets
R1(config-router)#summary-address 16.0.0.0 252.0.0.0
The summary handle appears on R2, a downstream router.
R2#exhibit ip route ospf
O E2 16.0.0.0/six [one hundred ten/20] via 172.12.123.one, 00:00:05, Serial0
Let’s go back to R1 and check out its OSPF table.
R1#show ip route ospf
O 16.0.0.0/six is actually a summary, 00:01:fifty one, Null0
Exactly where did the null0 interface originate from, and why is it there? Packets despatched on the null interface are dropped, and in this case, that’s an excellent thing.
When you configure summary routes in OSPF, a path to null0 will be mounted into your OSPF routing desk. This assists to circumvent routing loops. Any packets destined to the routes that have been summarized should have a longer match inside the routing table, as revealed down below…
C 17.0.0.0/eight is immediately connected, Loopback17
C sixteen.0.0.0/8 is immediately connected, Loopback16
C 19.0.0.0/eight is immediately connected, Loopback19
C eighteen.0.0.0/eight is directly connected, Loopback18
O sixteen.0.0.0/6 is actually a summary, 00:01:51, Null0
.. and packets that don't match on the list of summarized routes but do match the summary route are going to be dropped.
Preventing routing 먹튀 loops when executing route redistribution and summarization is important. OSPF provides us somewhat help in that regard in this example, and as you examine much more elaborate redistribution scenarios on your own solution to the CCNP and CCIE, you’ll recognize that we’ll consider all the help we could possibly get!