OSPF is a field matter on both the CCNA and CCNP exams, and it's also the matter that requires the most tending to detail. Where impulsive routing protocols much as RIP and IGRP hit exclusive digit router type, a countenance at a Cisco routing plateau shows individual assorted OSPF distinction types.
R1#show ip route
Codes:
C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA outside identify 1, N2 - OSPF NSSA outside identify 2
E1 - OSPF outside identify 1, E2 - OSPF outside identify 2, E - EGP
In this tutorial, we'll verify a countenance at the disagreement between digit of these distinction types, E1 and E2.
Route redistribution is the impact of attractive routes scholarly via digit routing prescript and injecting those routes into added routing domain. (Static and adjoining routes crapper also be redistributed.) When a router streaming OSPF takes routes scholarly by added routing prescript and makes them acquirable to the another OSPF-enabled routers it's act with, that router becomes an Autonomous System Border Router (ASBR).
Let's impact with an warning where R1 is streaming both OSPF and RIP. R4 is in the aforementioned OSPF field as R1, and we poverty R4 to see the routes that R1 is acquisition via RIP. This effectuation we hit to action distinction redistribution on the ASBR. The routes that are existence redistributed from RIP into OSPF module materialize as E2 routes on R4:
R4#show ip distinction ospf
O E2 5.1.1.1 [110/20 via 172.34.34.3, 00:33:21, Ethernet0
6.0.0.0/32 is subnetted, 1 subnets
O E2 6.1.1.1 [110/20 via 172.34.34.3, 00:33:21, Ethernet0
172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks
O E2 172.12.21.0/30 [110/20 via 172.34.34.3, 00:33:32,
Ethernet0
O E2 7.1.1.1 [110/20 via 172.34.34.3, 00:33:21, Ethernet0
15.0.0.0/24 is subnetted, 1 subnets
O E2 15.1.1.0 [110/20 via 172.34.34.3, 00:33:32, Ethernet0
E2 is the choice distinction identify for routes scholarly via redistribution. The key with E2 routes is that the outlay of these routes reflects exclusive the outlay of the distinction from the ASBR to the test destination; the outlay of the distinction from R4 to R1 is not echolike in this cost. (Remember that OSPF's amount for a distinction is referred to as cost.)
In this example, we poverty the outlay of the routes to emit the whole path, not meet the distinction between the ASBR and the instruction network. To do so, the routes staleness be redistributed into OSPF as E1 routes on the ASBR, as shown here.
R1#conf t
Enter plan commands, digit per line. End with CNTL/Z.
R1(config)#router ospf 1
R1(config-router)#redistribute countercurrent subnets metric-type 1
Now on R4, the routes materialize as E1 routes and hit a large metric, since the whole distinction outlay is today echolike in the routing table.
O E1 5.1.1.1 [110/94 via 172.34.34.3, 00:33:21, Ethernet0
6.0.0.0/32 is subnetted, 1 subnets
O E1 6.1.1.1 [110/100 via 172.34.34.3, 00:33:21, Ethernet0
172.12.0.0/16 is variably subnetted, 2 subnets, 2 masks
O E1 172.12.21.0/30 [110/94 via 172.34.34.3, 00:33:32, Ethernet0
O E1 7.1.1.1 [110/94 via 172.34.34.3, 00:33:21, Ethernet0
15.0.0.0/24 is subnetted, 1 subnets
O E1 15.1.1.0 [110/94 via 172.34.34.3, 00:33:32, Ethernet0
Knowing the disagreement between E1 and E2 routes is alive for CCNP communicating success, as substantially as full discernment a creation router's routing table. Good phenomenon in your studies!
Chris Bryant, CCIE #12933, is the someone of The Bryant Advantage, bag of liberated CCNP and CCNA tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
For a FREE double of his stylish e-books, How To Pass The CCNA and How To Pass The CCNP, meet meet the website! You crapper also intend FREE CCNA and CCNP communicating questions every day! Pass the CCNP communicating with The Bryant Advantage!
