Cisco OSPF Command and Configuration Handbook (paperback)
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6-6 distance ospf intra-area administrative-distance
Syntax Description:
Purpose: If a router has learned about a network from more than one routing protocol, then the administrative distance is used to select the best route. The best route is the route that will be installed in the IP routing table, the route with the lowest administrative distance. The default administrative distances for the IP routing protocols are:
There are three types of OSPF routes. These types are external (either type 1 or 2), inter-area, and intra-area. External routes are those that have been redistributed into OSPF. A route to an area directly connected to the router is an intra-area route and a route to an area that is not directly connected to the router is an inter-area route. These commands are used to modify the administrative distance of all routes belonging to one of the three types of OSPF routes. Initial Cisco IOS Software Release: 11.1 Configuration Example: Adjusting the Administrative Distance Based on the Type of OSPF Route
In Figure 6-3, Router A is receiving two OSPF external routes from the redistribution of EIGRP on Router B. Router A is also receiving an OSPF inter-area route and an OSPF intra-area route from Router B. Figure 6-3. The Three Types of OSPF Routes Are Inter-area, Intra-area, and External
Router A interface Loopback0 ip address 1.1.1.1 255.255.255.255 ! interface Ethernet0/0 ip address 172.16.1.1 255.255.255.0 ! router ospf 1 network 1.1.1.1 0.0.0.0 area 1 network 172.16.1.0 0.0.0.255 area 0 ________________________________________________________________________________ Router B interface Loopback0 ip address 2.2.2.2 255.255.255.255 ! interface Loopback1 ip address 51.51.51.51 255.255.255.0 ! interface Ethernet0 ip address 172.16.1.2 255.255.255.0 ! interface Serial1 bandwidth 64 ip address 10.1.1.5 255.255.255.252 clockrate 64000 ! router eigrp 1 network 10.0.0.0 ! router ospf 1 router-id 2.2.2.2 redistribute eigrp 1 subnets network 2.2.2.2 0.0.0.0 area 2 network 51.51.51.51 0.0.0.0 area 0 network 172.16.1.0 0.0.0.255 area 0 ________________________________________________________________________________ Router C interface Loopback0 ip address 3.3.3.3 255.255.255.0 ! interface Serial0 bandwidth 64 ip address 10.1.1.6 255.255.255.252 ! router eigrp 1 network 3.0.0.0 network 10.0.0.0 no auto-summary Verify that Routers A and B have established an OSPF neighbor relationship. rtrA# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 1 FULL/BDR 00:00:30 172.16.1.2 Ethernet0/0 ________________________________________________________________________________ rtrB# show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 1.1.1.1 1 FULL/DR 00:00:38 172.16.1.1 Ethernet0 Verify that Routers B and C have formed an EIGRP relationship. rtrB# show ip eigrp neighbors IP-EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 10.1.1.6 Se1 10 00:13:27 399 2394 0 4 ________________________________________________________________________________ rtrC# show ip eigrp neighbors IP-EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 10.1.1.5 Se0 11 00:13:53 28 2280 0 6 Verify that Router A is learning each type of OSPF route. rtrA# 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 external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1, E2 - OSPF external type 2 , E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route, o - ODR Gateway of last resort is not set 51.0.0.0/32 is subnetted, 1 subnets O 51.51.51.51 [110/11] via 172.16.1.2, 00:21:44, Ethernet0/0 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 2.0.0.0/32 is subnetted, 1 subnets O IA 2.2.2.2 [110/11] via 172.16.1.2, 00:21:44, Ethernet0/0 3.0.0.0/24 is subnetted, 1 subnets O E2 3.3.3.0 [110/20] via 172.16.1.2, 00:21:44, Ethernet0/0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, Ethernet0/0 10.0.0.0/30 is subnetted, 1 subnets O E2 10.1.1.4 [110/20] via 172.16.1.2, 00:21:44, Ethernet0/0 Modify the configuration on Router A to set the administrative distance of OSPF inter-area routes to 60, intra-area routes to 70, and external routes to 50. Router A router ospf 1 network 1.1.1.1 0.0.0.0 area 1 network 3.3.3.0 0.0.0.255 area 0 network 172.16.1.0 0.0.0.255 area 0 distance ospf intra-area 70 inter-area 60 external 50 Verification
Verify that the different OSPF route types have been configured with the proper administrative distance. rtrA# 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 external type 1, N2 - OSPF NSSA external type 2 E1 - OSPF external type 1 , E2 - OSPF external type 2 , E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route, o - ODR Gateway of last resort is not set 51.0.0.0/32 is subnetted, 1 subnets O 51.51.51.51 [ 70 /11] via 172.16.1.2, 00:02:04, Ethernet0/0 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 2.0.0.0/32 is subnetted, 1 subnets O IA 2.2.2.2 [ 60 /11] via 172.16.1.2, 00:02:04, Ethernet0/0 3.0.0.0/24 is subnetted, 1 subnets O E2 3.3.3.0 [ 50 /20] via 172.16.1.2, 00:02:04, Ethernet0/0 172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, Ethernet0/0 10.0.0.0/30 is subnetted, 1 subnets O E2 10.1.1.4 [ 50 /20] via 172.16.1.2, 00:02:04, Ethernet0/0 Troubleshooting
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