BSCI Exam Success, Not To Mention Earning Your CCNP, Can Come Down To Your OSPF Route Summarization Skills. There Are A Few Different Commands And Situations You Need To Be Ready For, And One Of These Situations Is The Proper Use Of The "summary-address" Command.The Summary-address Command Should Be Used On An ASBR In Order To Summarize Routes That Are Being Injected Into The OSPF Domain Via Redistribution. In The Following Example, Four Routes Are Being Redisitributed Into OSPF On R1, Making R1 An ASBR.interface Loopback16ip Address 16.16.16.16 255.0.0.0!interface Loopback17ip Address 17.17.17.17 255.0.0.0!interface Loopback18ip Address 18.18.18.18 255.0.0.0!interface Loopback19ip Address 19.19.19.19 255.0.0.0R1(config)router Ospf 1R1(config-router)redistribute Connected Subnets These Four Routes Are Seen On Downstream Router R2 As External Type-2, The Default For Routes Redistributed Into OSPF.R2show Ip Route OspfO E2 17.0.0.08 11020 Via 172.12.123.1, 00:00:07, Serial0O E2 16.0.0.08 11020 Via 172.12.123.1, 00:00:07, Serial0O E2 19.0.0.08 11020 Via 172.12.123.1, 00:00:07, Serial0O E2 18.0.0.08 11020 Via 172.12.123.1, 00:00:07, Serial0To Summarize Networks Learned By Redistribution, Use The OSPF Command Summary-address. You Can Probably Do This Summarization In Your Head, But Do So Before Continuing With The Lab.R1(config)router Ospf 1R1(config-router)summary-address 16.0.0.0 252.0.0.0Look At The Change In R2's OSPF Table.R2show Ip Route OspfO E2 16.0.0.06 11020 Via 172.12.123.1, 00:00:05, Serial0The External Routes Have Been Successfully Summarized. Note That The Summary Route Is Still Marked As An E2 Route.There's An Interesting Route Installed Into R1's OSPF Table As Well.R1show Ip Route OspfO 16.0.0.06 Is A Summary, 00:01:51, Null0When You Configure Summary Routes In OSPF, A Route To Null0 Will Be Installed Into The OSPF Routing Table. This Helps To Prevent Routing Loops. Any Packets Destined For The Routes That Have Been Summarized Will Have A Longer Match In The Routing Table.... C 17.0.0.08 Is Directly Connected, Loopback17C 16.0.0.08 Is Directly Connected, Loopback16C 19.0.0.08 Is Directly Connected, Loopback19C 18.0.0.08 Is Directly Connected, Loopback18O 16.0.0.06 Is A Summary, 00:03:10, Null0O 12.0.0.06 Is A Summary, 00:07:53, Null0.. And Packets That Do Not Match One Of The Summarized Routes But Do Match The Summary Route Will Be Dropped.
