CCNP / BSCI Exam Tutorial: Route Summarization Plus the OSPF Null Interface
CCNP Examination good results, specially about the BSCI Examination, needs you recognize the main points of route summarization. This ability not merely needs that you've got a convenience level with binary conversions, but You will need to understand how and the place to use route summarization with Every unique protocol.
You also have to be aware of the “Unintended effects” of route summarization. With OSPF, there'll really be an additional interface established at The purpose of summarization, and this catches a great deal of CCNP candidates by surprise. Let’s Consider the null0 interface and how it relates to OSPF summarization.
On R1, the next networks are redistributed into OSPF, after which you can summarized.
interface Loopback16
ip handle sixteen.sixteen.sixteen.sixteen 255.0.0.0
interface Loopback17
ip handle seventeen.17.17.seventeen 255.0.0.0
interface Loopback18
ip handle 18.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 linked subnets
R1(config-router)#summary-tackle sixteen.0.0.0 252.0.0.0
The summary address appears on R2, a downstream router.
R2#clearly show ip route ospf
O E2 16.0.0.0/6 [a hundred and ten/20] through 172.12.123.one, 00:00:05, Serial0
Allow’s go back to R1 and evaluate its OSPF desk.
R1#clearly show ip route ospf
O 16.0.0.0/six is 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 먹튀 dropped, and in this case, that’s an excellent factor.
Once you configure summary routes in OSPF, a route to null0 are going to be put in in the OSPF routing table. This helps to circumvent routing loops. Any packets destined to the routes that were summarized may have an extended match from the routing desk, as shown below…
C 17.0.0.0/8 is instantly connected, Loopback17
C 16.0.0.0/8 is specifically linked, Loopback16
C 19.0.0.0/8 is specifically related, Loopback19
C 18.0.0.0/eight is straight related, Loopback18
O 16.0.0.0/six is actually a summary, 00:01:fifty one, Null0
.. and packets that do not match one of many summarized routes but do match the summary route will be dropped.
Blocking routing loops when doing route redistribution and summarization is significant. OSPF offers us just a little help in that regard in this case, and while you analyze extra complicated redistribution scenarios on the solution to the CCNP and CCIE, you’ll realize that we’ll take all the help we can get!