Not-So-Stubby Area
This section contains OSPFv3 NSSA (Not-So-Stubby Area) configuration examples.
An NSSA allows external routes to be advertised into the OSPF autonomous system while retaining the characteristics of a stub area to the rest of the autonomous system. To do this, the ASBR in an NSSA will originate type 7 LSAs to advertise the external destinations. These NSSA external LSAs are flooded throughout the NSSA but are blocked at the ABR.
The NSSA external LSA has a flag in its header known as the P-bit. The NSSA ASBR has the option of setting or clearing the P-bit. If an NSSA’s ABR receives a type 7 LSA with the P-bit set to one, it translates the type 7 LSA into a type 5 LSA and floods it throughout the other areas. If the P-bit is set to zero, no translation takes place and the destination in the type 7 LSA is not advertised outside of the NSSA.
Topology
Figure 12-92: Translating Type 7 LSAs into Type 5 LSAs
NSSA with Route Option
This example shows the configuration to enable NSSA and to configure different route options for NSSA. There are three area nssa command options for originating default Type-3 LSA and default Type-7 LSA, and for blocking redistribution of Type-7 LSA into an NSSA:
• no-summary: The NSSA ABR blocks all type-3 and type-4 LSAs into the NSSA area and sends a single type-3 LSA into the area to advertise a default route
• default-information-originate: The NSSA ABR advertises a default route into the NSSA as a type-7 LSA.
• no-redistribution: The NSSA ABR bocks type-7 LSA from being redistributed into the NSSA area.
In Figure 12-93, R2 is an NSSA ABR as well as an NSSA ASBR that maps the router interfaces to two different areas and redistributes the connected routes of the loopback interface. Also, this example sets the no-summary, no-redistribution, and default-information-originate options on R2 to originate default Type-3 LSAs and default Type-7 LSAs into the NSSA and to block Type-7 LSAs.
Topology
Figure 12-93: NSSA with Route Options
R1
(config)#interface eth1 | Enter interface mode for eth1. |
(config-if)#ipv6 router ospf tag 100 area 1 | Configure interface in an area assigned with the area ID (1). |
(config-if)#exit | Exit interface mode. |
(config)#router ipv6 ospf 100 | Configure the routing process and specify the tag (100). |
(config-router)#router-id 10.10.10.10 | Configure the router ID to use on this instance (100) |
(config-router)#area 1 nssa | Configure area as NSSA |
(config-router)#commit | Commit the candidate configuration to the running configuration. |
(config-router)#exit | Exit interface mode |
R2
(config)#interface eth1 | Enter interface mode for eth1. |
(config-if)#ipv6 router ospf tag 100 area 1 | Configure interface in an area assigned with the area ID (1). |
(config-if)#exit | Exit interface mode. |
(config)#interface eth2 | Enter interface mode for eth2 |
(config-if)#ipv6 router ospf tag 100 area 0 | Configure interface in backbone |
(config-if)#interface lo | Enter interface mode for Loopback |
(config-if)#ipv6 address 8000::24b:0:0:0:0/64 | Assign IPv6 address to loopback interface |
(config-if)#ipv6 address 8000::250:0:0:0:0/64 | Assign IPv6 address to loopback interface |
(config-if)#ipv6 address 8000::27d:0:0:0:0/64 | Assign IPv6 address to loopback interface |
(config-if)#ipv6 address 8000::27e:0:0:0:0/64 | Assign IPv6 address to loopback interface |
(config-if)#commit | Commit the candidate configuration to the running configuration. |
(config-if)#exit | Exit interface mode. |
(config)#router ipv6 ospf 100 | Configure the routing process and specify the tag (100). |
(config-router)#router-id 20.20.20.20 | Configure the router ID to use on this instance (100) |
(config-router)#redistribute connected | Redistribute the configured loopback network into the NSSA |
(config-router)#area 1 nssa no-redistribution default-information-originate no-summary | Configure the Router to originate default Type-3 LSAs and default Type-7 LSAs, and to block Type-7 LSAs into the NSSA |
(config-router)#commit | Commit the candidate configuration to the running configuration. |
(config-router)#exit | Exit interface mode |
R3
(config)#interface eth1 | Enter interface mode for eth1. |
(config-if)#ipv6 router ospf tag 100 area 0 | Configure interface in an area assigned with the area ID (1). |
(config-if)#exit | Exit interface mode. |
(config)#router ipv6 ospf 100 | Configure the routing process and specify the tag (100). |
(config-router)#router-id 30.30.30.30 | Configure the router ID to use on this instance (100) |
(config-router)#commit | Commit the candidate configuration to the running configuration. |
(config-router)#exit | Exit interface mode |
Validation 1
In the output of show ipv6 ospf neighbor below, verify that OSPFv3 adjacency is in state “full” for both R1 and R2 under the process identifier 100.
R1#sh ipv6 ospf neighbor
OSPFv3 Process (100)
Neighbor ID Pri State Dead Time Interface Instance ID
20.20.20.20 1 Full/DR 00:00:34 eth1 0
R2#show ipv6 ospf neighbor
Total number of full neighbors: 2
OSPFv3 Process (100)
Neighbor ID Pri State Dead Time Interface Instance ID
10.10.10.10 1 Full/DR 00:00:36 eth1 0
30.30.30.30 1 Full/Backup 00:00:39 eth2 0
R2#
Validation 2
The output below shows originating default Type-3 LSAs into the NSSA with the no-summary option. The advertising router identifier is for R2 (20.20.20.20, the NSSA-ABR). Also, the prefix is ::/0 and the LS-Type is Inter-Area-Prefix-LSA for the default Type-3 LSA route into the NSSA.
R1#sh ipv6 ospf database inter-prefix
OSPFv3 Router with ID (10.10.10.10) (Process 100)
Inter-Area-Prefix-LSA (Area 0.0.0.1)
LS age: 1234
LS Type: Inter-Area-Prefix-LSA
Link State ID: 0.0.0.6
Advertising Router: 20.20.20.20
LS Seq Number: 0x80000001
Checksum: 0x17D0
Length: 28
Metric: 1
Prefix: ::/0
Prefix Options: 0
Validation 3
The output below shows originating default type-7 LSAs alone after setting the no-redistribution and default-information originate options. The advertising router identifier is for R2 (20.20.20.20, the NSSA-ABR). Also, the prefix is ::/0 and LS-Type is NSSA-external-LSA for the default Type-7 LSA route into the NSSA
R1#sh ipv6 ospf database nssa-external
OSPFv3 Router with ID (10.10.10.10) (Process 100)
NSSA-external-LSA (Area 0.0.0.1)
LS age: 1758
LS Type: NSSA-external-LSA
Link State ID: 0.0.0.20
Advertising Router: 20.20.20.20
LS Seq Number: 0x80000002
Checksum: 0x6468
Length: 32
Metric Type: 2 (Larger than any link state path)
Metric: 1
Prefix: ::/0
Prefix Options: 0 (-|-|-|-)
External Route Tag: 0
Last modified date: 10/16/2023