CCNP / BSCI Exam Tutorial: Route Summarization And The OSPF Null Interface

Computer and Technology - CCNP exam success, particularly in the BSCI exam, demands you understand the details of route summarization. This skill not just requires that have the ear of a comfort level with binary conversions, but you need to understand how and where to use route summarization with each protocol. 

CCNP / BSCI Exam Tutorial:  Route Summarization And The OSPF Null Interface

CCNP / BSCI Exam Tutorial: Route Summarization And The OSPF Null Interface

 You might also need to understand the "side effects" of route summarization. With OSPF, There‘ll be an additional interface created in the point of summarization, which catches lots of CCNP candidates by surprise. Let us check out the null0 interface and just how it pertains to OSPF summarization. 

 On R1, the listed networks are redistributed into OSPF, after which summarized. 

 interface Loopback16 

 IP address 16. 16. 16. 16 255. 0. 0. 0 
interface Loopback17 

 IP address 17. 17. 17. 17 255. 0. 0. 0 
interface Loopback18 

 IP address 18. 18. 18. 18 255. 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 address appears on R2, a downstream router. 

 R2#show ip route OSPF 
O E2 16. 0. 0. 0 / 6 110 / 20 via 172. 12. 123. 1, 00 : 00 : 05, Serial0 
Let us go to R1 and look into its OSPF table. 

 R1#show ip route OSPF 
O 16. 0. 0. 0 / 6 is really a summary, 00 : 01 : 51, Null0 

 Where did the null0 interface derive from, and why can it be there? Packets sent towards the null interface are dropped, and during this case, that is a very good thing. 

 Whenever you configure summary routes in OSPF, a route to null0 will certainly be installed straight into the OSPF routing table. This helps to avoid routing loops. Any packets destined to the routes which have been summarized will possess a longer match inside the routing table, as shown below... 

 C 17. 0. 0. 0 / 8 is directly connected, Loopback17 

 C 16. 0. 0. 0 / 8 is directly connected, Loopback16 

 C 19. 0. 0. 0 / 8 is directly connected, Loopback19 

 C 18. 0. 0. 0 / 8 is directly connected, Loopback18 

 O 16. 0. 0. 0 / 6 is really a summary, 00 : 01 : 51, Null0 
.. and packets that don‘t match perhaps one of the summarized routes but do match the summary route will certainly be dropped. 

 Preventing routing loops when performing route redistribution and summarization is vital. OSPF gives us just a little assist in that regard during this situation, and also as you study more complex redistribution scenarios on your path towards the CCNP and CCIE, you will understand that we will take all of the help we will get!

 I think it's enough all about CCNP / BSCI Exam Tutorial:  Route Summarization And The OSPF Null Interface. Thanks so much :)

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