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CCNP / BSCI Examination Tutorial: Route Summarization As well as OSPF Null Interface

CCNP Examination accomplishment, specifically around the BSCI Test, demands you fully grasp the details of route summarization. This ability not simply requires that you have a comfort degree with binary conversions, but You must understand how and where to apply route summarization with Each and every specific protocol.

You also have to understand the “Negative effects” of route summarization. With OSPF, there will truly be an extra interface made at The purpose of summarization, which catches a lot of CCNP candidates by surprise. Enable’s Consider the null0 interface And exactly how it pertains to OSPF summarization.

On R1, the subsequent networks are redistributed into OSPF, after which you can summarized.

interface Loopback16

ip deal with sixteen.16.16.16 255.0.0.0

interface Loopback17

ip deal with 17.seventeen.seventeen.seventeen 255.0.0.0

image

interface Loopback18

ip address eighteen.18.eighteen.18 255.0.0.0

interface Loopback19

ip handle 19.19.19.19 255.0.0.0

R1(config)#router ospf one

R1(config-router)#redistribute linked subnets

R1(config-router)#summary-deal 토토 with 16.0.0.0 252.0.0.0

The summary deal with seems on R2, a downstream router.

R2#exhibit ip route ospf

O E2 sixteen.0.0.0/six [one hundred ten/20] by means of 172.12.123.1, 00:00:05, Serial0

Allow’s go back to R1 and have a look at its OSPF desk.

R1#exhibit ip route ospf

O 16.0.0.0/6 can be a summary, 00:01:fifty one, Null0

Where by did the null0 interface come from, and why could it be there? Packets despatched on the null interface are dropped, and In cases like this, that’s a very good factor.

Whenever you configure summary routes in OSPF, a path to null0 are going to be installed in to the OSPF routing desk. This will help to forestall routing loops. Any packets destined for your routes that have been summarized could have a longer match during the routing desk, as demonstrated under…

C seventeen.0.0.0/8 is specifically connected, Loopback17

C sixteen.0.0.0/8 is straight linked, Loopback16

C 19.0.0.0/8 is right connected, Loopback19

C eighteen.0.0.0/eight is straight connected, Loopback18

O 16.0.0.0/six is really a summary, 00:01:51, Null0

.. and packets that don't match one of the summarized routes but do match the summary route are going to be dropped.

Preventing routing loops when doing route redistribution and summarization is vital. OSPF gives us just a little help in that regard in this example, and while you analyze more intricate redistribution scenarios in your approach to the CCNP and CCIE, you’ll recognize that we’ll just take all the assistance we can get!