2-7 area area-id nssa no-summary
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2-7 area area-id nssa no-summarySyntax Description:
Purpose: This command is used on an OSPF ABR to block OSPF inter-area routes from entering an NSSA. This command will also generate an OSPF inter-area default route into the NSSA. This will make the NSSA a totally stubby area. In a stub or totally stubby area, the ABR to the stub area will prevent OSPF external routes (type 5) from being advertised into the stub area. This implies that an ASBR cannot be part of a stubby or totally stubby area because an ASBR generates OSPF external type 5 routes. Situations arise where you want to create a stubby or totally stubby area relative to OSPF but also want to advertise redistributed routes from an ASBR across the area. An OSPF area that has these properties is an NSSA. In Figure 2-7, you want Router B, the ABR, to block OSPF external routes and OSPF inter-area routes from Area 1 and advertise a default route into the NSSA. You also want the routes redistributed by Router C, the ASBR, to be allowed into the area. If you configure Area 1 as an NSSA, then the external OSPF routes that Router B receives from Area 0 will be blocked from Area 1. The redistributed routes from the ASBR will be sent as OSPF type 7 routes. Router B will convert these type 7 routes to OSPF type 5 routes and advertise them into Area 0. Normally, routes redistributed into OSPF are type 5 routes. An ASBR that has been configured as an NSSA will generate type 7 routes instead of type 5 routes. By default, an ABR does not generate a default route into an NSSA. Figure 2-7. A Totally Stubby NSSA Initial Cisco IOS Software Release: 11.2 Configuration Example: Creating a Totally Stubby NSSAIn Figure 2-7, Routers C and D are running RIP version 2. Router D is advertising the networks 156.26.32.0/24 and 156.26.33.0/24 to Router C via RIP. Router C will redistribute the RIP routes, including the 10.1.1.8/30 network, into OSPF. Because Area 1 has been defined as an NSSA, the redistributed RIP routes will be advertised into Area 1 as OSPF type 7 routes. Initially we will configure Area 1 as a normal OSPF area in order to see the routes that are advertised. Router A interface Loopback0 ip address 1.1.1.1 255.255.255.255 ! interface Serial0/1 ip address 10.1.1.1 255.255.255.252 clockrate 64000 ! router ospf 1 redistribute connected subnets network 10.1.1.0 0.0.0.3 area 0 _______________________________________________________________________ Router B interface Loopback0 ip address 2.2.2.2 255.255.255.255 ! interface Serial0 ip address 10.1.1.2 255.255.255.252 ! interface Serial1 ip address 10.1.1.5 255.255.255.252 lockrate 64000 ! router ospf 1 network 10.1.1.0 0.0.0.3 area 0 network 10.1.1.4 0.0.0.3 area 1 _______________________________________________________________________ Router C interface Loopback0 ip address 3.3.3.3 255.255.255.255 ! interface Serial0 ip address 10.1.1.6 255.255.255.252 ! interface Serial1 ip address 10.1.1.10 255.255.255.252 clockrate 64000 ! router ospf 1 redistribute rip subnets network 10.1.1.4 0.0.0.3 area 1 ! router rip version 2 passive-interface Serial0 network 10.0.0.0 _______________________________________________________________________ Router D interface Loopback0 ip address 156.26.32.1 255.255.255.0 ! interface Loopback1 ip address 156.26.33.1 255.255.255.0 ! interface Serial0/0 ip address 10.1.1.9 255.255.255.252 ! router rip version 2 network 10.0.0.0 network 156.26.0.0 no auto-summary Router A is advertising Loopback0 as an OSPF type 5 external route because this route was injected into OSPF through redistribution. Routers A and B are also learning the redistributed RIP routes as external type 5 OSPF routes. 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 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 156.26.0.0/24 is subnetted, 2 subnets O E2 156.26.32.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1 O E2 156.26.33.0 [110/20] via 10.1.1.2, 00:02:25, Serial0/1 10.0.0.0/30 is subnetted, 3 subnets O E2 10.1.1.8 [110/20] via 10.1.1.2, 00:02:25, Serial0/1 C 10.1.1.0 is directly connected, Serial0/1 O IA 10.1.1.4 [110/128] via 10.1.1.2, 00:02:25, Serial0/1 _______________________________________________________________________ rtrB# 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 1.0.0.0/32 is subnetted, 1 subnets O E2 1.1.1.1 [110/20] via 10.1.1.1, 00:04:14, Serial0 2.0.0.0/32 is subnetted, 1 subnets C 2.2.2.2 is directly connected, Loopback0 156.26.0.0/24 is subnetted, 2 subnets O E2 156.26.32.0 [110/20] via 10.1.1.6, 00:04:14, Serial1 O E2 156.26.33.0 [110/20] via 10.1.1.6, 00:04:14, Serial1 10.0.0.0/30 is subnetted, 3 subnets O E2 10.1.1.8 [110/20] via 10.1.1.6, 00:04:14, Serial1 C 10.1.1.0 is directly connected, Serial0 C 10.1.1.4 is directly connected, Serial1 Router C is learning the network redistributed by Router A as an OSPF external type 5 route. rtrC# 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 1.0.0.0/32 is subnetted, 1 subnets O E2 1.1.1.1 [110/20] via 10.1.1.5, 00:06:24, Serial0 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 156.26.0.0/24 is subnetted, 2 subnets R 156.26.32.0 [120/1] via 10.1.1.9, 00:00:18, Serial1 R 156.26.33.0 [120/1] via 10.1.1.9, 00:00:18, Serial1 10.0.0.0/30 is subnetted, 3 subnets C 10.1.1.8 is directly connected, Serial1 O IA 10.1.1.0 [110/128] via 10.1.1.5, 00:06:24, Serial0 C 10.1.1.4 is directly connected, Serial0 Now modify the OSPF configurations on Routers B and C in order to create the NSSA. Router B router ospf 1 area 1 nssa network 10.1.1.0 0.0.0.3 area 0 network 10.1.1.4 0.0.0.3 area 1 _______________________________________________________________________ Router C router ospf 1 area 1 nssa redistribute rip subnets network 10.1.1.4 0.0.0.3 area 1 Verify that Area 1 has been configured as an NSSA. rtrB# show ip ospf Routing Process "ospf 1" with ID 2.2.2.2 Supports only single TOS(TOS0) routes It is an area border and autonomous system boundary router Redistributing External Routes from, SPF schedule delay 5 secs, Hold time between two SPFs 10 secs Minimum LSA interval 5 secs. Minimum LSA arrival 1 secs Number of external LSA 5. Checksum Sum 0x324D4 Number of DCbitless external LSA 0 Number of DoNotAge external LSA 0 Number of areas in this router is 2. 1 normal 0 stub 1 nssa Area BACKBONE(0) Number of interfaces in this area is 1 Area has no authentication SPF algorithm executed 11 times Area ranges are Number of LSA 3. Checksum Sum 0x20790 Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Area 1 Number of interfaces in this area is 1 It is a NSSA area Perform type-7/type-5 LSA translation Area has no authentication SPF algorithm executed 22 times Area ranges are Number of LSA 7. Checksum Sum 0x26D1D Number of DCbitless LSA 0 Number of indication LSA 0 Number of DoNotAge LSA 0 Now inspect the routing tables on Routers A, B, and C to view the effect of configuring Area 1 as an NSSA. rtrB# 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 1.0.0.0/32 is subnetted, 1 subnets O E2 1.1.1.1 [110/20] via 10.1.1.1, 00:03:55, Serial0 2.0.0.0/32 is subnetted, 1 subnets C 2.2.2.2 is directly connected, Loopback0 156.26.0.0/24 is subnetted, 2 subnets O N2 156.26.32.0 [110/20] via 10.1.1.6, 00:03:55, Serial1 O N2 156.26.33.0 [110/20] via 10.1.1.6, 00:03:55, Serial1 10.0.0.0/30 is subnetted, 3 subnets O N2 10.1.1.8 [110/20] via 10.1.1.6, 00:03:55, Serial1 C 10.1.1.0 is directly connected, Serial0 C 10.1.1.4 is directly connected, Serial1 The redistributed RIP routes have been converted from OSPF E2 routes to OSPF N2 routes. This means that the redistributed RIP routes are now being advertised as type 7 routes instead of type 5 routes. On Router A, these routes should still be OSPF type 5 routes because Router B is converting them from type 7 to type 5. 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 1.0.0.0/32 is subnetted, 1 subnets C 1.1.1.1 is directly connected, Loopback0 156.26.0.0/24 is subnetted, 2 subnets O E2 156.26.32.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1 O E2 156.26.33.0 [110/20] via 10.1.1.2, 00:07:28, Serial0/1 10.0.0.0/30 is subnetted, 3 subnets O E2 10.1.1.8 [110/20] via 10.1.1.2, 00:07:28, Serial0/1 C 10.1.1.0 is directly connected, Serial0/1 O IA 10.1.1.4 [110/128] via 10.1.1.2, 00:08:31, Serial0/1 Finally, inspect the IP routing table on Router C. rtrC# 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 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 156.26.0.0/24 is subnetted, 2 subnets R 156.26.32.0 [120/1] via 10.1.1.9, 00:00:10, Serial1 R 156.26.33.0 [120/1] via 10.1.1.9, 00:00:10, Serial1 10.0.0.0/30 is subnetted, 3 subnets C 10.1.1.8 is directly connected, Serial1 O IA 10.1.1.0 [110/128] via 10.1.1.5, 00:08:58, Serial0 C 10.1.1.4 is directly connected, Serial0 The 1.1.1.1 route that Router A was advertising as an OSPF external type 5 route has been blocked from entering the NSSA area by Router B, but the inter-area routes have been permitted. Also notice that unlike a stub or totally stubby area, there is no default route advertised by the ABR or ASBR. Modify the configuration on Router B in order to generate a default route into the NSSA and to block OSPF inter-area routes. Router B router ospf 1 area 1 nssa no-summary network 10.1.1.0 0.0.0.3 area 0 network 10.1.1.4 0.0.0.3 area 1 VerificationVerify that a default route is being advertised into the NSSA and that OSPF inter-area routes are being blocked by the ABR by inspecting the routing table on Router C. rtrC# 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 10.1.1.5 to network 0.0.0.0 3.0.0.0/24 is subnetted, 1 subnets C 3.3.3.0 is directly connected, Loopback0 156.26.0.0/24 is subnetted, 2 subnets R 156.26.32.0 [120/1] via 10.1.1.9, 00:00:25, Serial1 R 156.26.33.0 [120/1] via 10.1.1.9, 00:00:25, Serial1 10.0.0.0/30 is subnetted, 2 subnets C 10.1.1.8 is directly connected, Serial1 C 10.1.1.4 is directly connected, Serial0 O*IA 0.0.0.0/0 [110/65] via 10.1.1.5, 00:00:03, Serial0 Troubleshooting
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