2-5 area area-id nssa default-information-originate

 <  Free Open Study  >  

2-5 area area-id nssa default-information-originate

Syntax Description:

  • area-id ” OSPF area ID. This value can be entered as a decimal number in the range of 1 to 4,294,967,295 or in IP address form in the range 0.0.0.1 to 255.255.255.255. Area 0 can be entered, but Area 0 cannot be configured as an NSSA.

Purpose: This command is used on an OSPF ABR or an OSPF ASBR to generate an OSPF NSSA external type 2 default route into an NSSA. A default route does not need to be defined when using this command on an ABR. If this command is configured on an ASBR, then a default route needs to be configured. 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 since 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 2-5, you want Router B, the ABR, to block OSPF external 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 2-5. The default-information-originate Command Generates an OSPF NSSA Default Route into an OSPF NSSA

graphics/02fig05.gif

Initial Cisco IOS Software Release: 11.2

Configuration Example: Advertising an OSPF NSSA Default Route into an OSPF NSSA

In Figure 2-5, 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, you 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 Loopback 0 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 since 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 an OSPF NSSA default route into the NSSA.

 Router B  router ospf 1    area 1 nssa defalt-information-originate    network 10.1.1.0 0.0.0.3 area 0   network 10.1.1.4 0.0.0.3 area 1  
Verification

Verify that a default route is being advertised into the NSSA 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, 00:00:23, Serial1 R       156.26.33.0 [120/1] via 10.1.1.9, 00:00:23, 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, 00:14:39, Serial0 C       10.1.1.4 is directly connected, Serial0  O*N2 0.0.0.0/0 [110/1] via 10.1.1.5, 00:14:39, Serial0  
Troubleshooting
Step 1. Verify that there is a neighbor relationship between the OSPF routers by using the show ip ospf neighbor command.

Step 2. Verify that every router in the NSSA has been configured with the command area x nssa.

Step 3. The command option default-information-originate can only be used on the NSSA ABR or ASBR. Ensure that this command has been configured on either the ABR or ASBR.

 <  Free Open Study  >  


Cisco[r] OSPF Command and Configuration Handbook
Cisco OSPF Command and Configuration Handbook (paperback)
ISBN: 1587055406
EAN: 2147483647
Year: 2002
Pages: 236

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net