NSSA with the Translator Role Option
Type-7 to Type-5 translation is done by an NSSA-ABR. If an NSSA has multiple NSSA-ABRs, only one will perform the translation. The NSSA-ABR translator role options are:
• Candidate (default)
• Always
In the topology in Figure 12-95:
• R1 is NSSA-ASBR
• R2 and R3 are NSSA-ABRs
• R4 is a backbone router
In this example, the NSSA translator role candidate is configured on both NSSA-ABRs (R2 and R3). The Type-7 to Type-5 translation is done by the router with the higher router identifier (R3).
Topology
Figure 12-95: Using the translator-role Option
Configuration
When one NSSA-ABR is configured with the translator role as always and the other as candidate, then translation is done by the router configured as always. In this scenario, the translation can be biased by setting the translator role to always on the router that has the lower router identifier.
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)#interface eth2 | Enter interface mode for eth2. |
(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-if)#interface lo | Enter interface mode for Loopback |
(config-if)#ipv6 address 3333::1/64 | Assign IPv6 address to loopback interface |
(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 the area as NSSA. |
(config-router)#redistribute static | Redistribute the static route configured into the OSPF NSSA |
(config-router)#redistribute connected | Redistribute the connected network into OSPF NSSA |
(config-router)#commit | Commit the candidate configuration to the running configuration. |
(config-router)#exit | Exit interface mode |
(config)#ipv6 route 4444::1:0:0:0:0/64 6666::3 | Configure the static route with the nexthop address as R2’s eth1 IPv6 address |
(config)#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 area (0) |
(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)#area 1 nssa translator-role candidate | Configure the NSSA-ABR with the translator role candidate. |
(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 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 area (0) |
(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)#area 1 nssa translator-role candidate | Configure the NSSA-ABR with the translator role candidate. |
(config-router)#commit | Commit the candidate configuration to the running configuration. |
(config-router)#exit | Exit interface mode |
R4
(config)#interface eth1 | Enter interface mode for eth1. |
(config-if)#ipv6 router ospf tag 100 area 0 | Configure interface in backbone area (0) |
(config)#interface eth2 | Enter interface mode for eth2 |
(config-if)#ipv6 router ospf tag 100 area 0 | Configure interface in backbone area (0) |
(config-if)#exit | Exit interface mode. |
(config)#router ipv6 ospf 100 | Configure the routing process and specify the tag (100). |
(config-router)#router-id 40.40.40.40 | 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 |
The command to configure the NSSA-Translator role as always is:
(config-router)#area 1 nssa translator-role always
The NSSA-ABR can continue to perform translation after its services are no longer required for the stability interval which is set using the command below on the NSSA-ABR.
(config-router)#area 1 nssa stability-interval 7777
Validation 1
The translation is done by the NSSA-ABR with the higher router identifier. In the output below, check the router identifier of the NSSA-ABR. Also, check the router which is elected and the router which is disabled.
R2#sh ipv6 ospf
Routing Process "OSPFv3 (100)" with ID 20.20.20.20
Process uptime is 21 minutes
SPF schedule delay min 0.500 secs, SPF schedule delay max 50.0 secs
Minimum LSA interval 5 secs, Minimum LSA arrival 1 secs
Number of incoming current DD exchange neighbors 0/5
Number of outgoing current DD exchange neighbors 0/5
Number of external LSA 4. Checksum Sum 0x1F816
Number of AS-Scoped Unknown LSA 0
Number of LSA originated 28
Number of LSA received 58
Number of areas in this router is 2
Area BACKBONE(0)
Number of interfaces in this area is 1(1)
SPF algorithm executed 7 times
Number of LSA 19. Checksum Sum 0x7454D
Number of Unknown LSA 0
Area 0.0.0.1 (NSSA)
Number of interfaces in this area is 1(1)
SPF algorithm executed 14 times
Number of LSA 19. Checksum Sum 0xA4D18
Number of Unknown LSA 0
NSSA Translator State is disabled
R3#sh ipv6 ospf
Routing Process "OSPFv3 (100)" with ID 30.30.30.30
Process uptime is 19 minutes
SPF schedule delay min 0.500 secs, SPF schedule delay max 50.0 secs
Minimum LSA interval 5 secs, Minimum LSA arrival 1 secs
Number of incomming current DD exchange neighbors 0/5
Number of outgoing current DD exchange neighbors 0/5
Number of external LSA 4. Checksum Sum 0x1F816
Number of AS-Scoped Unknown LSA 0
Number of LSA originated 31
Number of LSA received 69
Number of areas in this router is 2
Area BACKBONE(0)
Number of interfaces in this area is 1(1)
SPF algorithm executed 15 times
Number of LSA 19. Checksum Sum 0x7454D
Number of Unknown LSA 0
Area 0.0.0.1 (NSSA)
Number of interfaces in this area is 1(1)
SPF algorithm executed 10 times
Number of LSA 19. Checksum Sum 0xA4D18
Number of Unknown LSA 0
NSSA Translator State is elected
Validation 2
The translated Type-5 LSA in R4 in area 0 has the advertising router identifier of R3. In the output below, the LS Type is AS-External-LSA and the advertising router has the higher router identifier.
R4#sh ipv6 ospf database external
OSPFv3 Router with ID (40.40.40.40) (Process 100)
AS-external-LSA
LS age: 885
LS Type: AS-External-LSA
Link State ID: 0.0.0.7
Advertising Router: 30.30.30.30
LS Seq Number: 0x80000001
Checksum: 0xD3FE
Length: 40
Metric Type: 2 (Larger than any link state path)
Metric: 20
Prefix: 3333::/64
Prefix Options: 0 (-|-|-|-)
External Route Tag: 0
LS age: 18
LS Type: AS-External-LSA
Link State ID: 0.0.0.8
Advertising Router: 30.30.30.30
LS Seq Number: 0x80000003
Checksum: 0x7457
Length: 56
Metric Type: 2 (Larger than any link state path)
Metric: 20
Prefix: 4444::/64
Prefix Options: 0 (-|-|-|-)
Forwarding Address: 6666::3
External Route Tag: 0
Last modified date: 10/16/2023