CCNP / BSCI Examination Tutorial: Route Summarization As well as the OSPF Null Interface
CCNP Examination results, significantly within the BSCI Test, requires you understand the small print of route summarization. This ability not only involves that you've a ease and comfort stage with binary conversions, but You need to understand how and exactly where to use route summarization with Each and every specific protocol.
You even have to learn the “Unwanted side effects” of route summarization. With OSPF, there will essentially be an additional interface made at the point of summarization, which catches a lot of CCNP candidates by surprise. Permit’s Look into the null0 interface And exactly how it relates to OSPF summarization.
On R1, the next networks are redistributed into OSPF, and then summarized.
interface Loopback16
ip deal with 16.16.16.sixteen 255.0.0.0
interface Loopback17
ip deal with seventeen.17.17.17 255.0.0.0
interface Loopback18
ip tackle 18.eighteen.18.eighteen 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 related subnets
R1(config-router)#summary-address 16.0.0.0 252.0.0.0
The summary tackle seems on R2, a downstream router.
R2#display ip route 토토 ospf
O E2 16.0.0.0/six [one hundred ten/twenty] via 172.12.123.one, 00:00:05, Serial0
Permit’s return to R1 and have a look at its OSPF table.
R1#clearly show ip route ospf
O 16.0.0.0/6 is actually a summary, 00:01:fifty one, Null0
Where by did the null0 interface come from, and why is it there? Packets despatched towards the null interface are dropped, and In this instance, that’s a fantastic point.
Any time you configure summary routes in OSPF, a route to null0 will likely be put in into your OSPF routing desk. This assists to avoid routing loops. Any packets destined for that routes that have been summarized will have a longer match in the routing desk, as revealed below…
C 17.0.0.0/eight is instantly related, Loopback17
C 16.0.0.0/8 is instantly connected, Loopback16
C 19.0.0.0/eight is directly connected, Loopback19
C 18.0.0.0/eight is directly related, Loopback18
O sixteen.0.0.0/6 is really a summary, 00:01:fifty one, Null0
.. and packets that don't match one of several summarized routes but do match the summary route will be dropped.
Blocking routing loops when undertaking route redistribution and summarization is important. OSPF presents us a bit assist in that regard in this example, and as you analyze much more sophisticated redistribution eventualities in your strategy to the CCNP and CCIE, you’ll understand that we’ll take all the help we could get!