Basic configuration of all routers:
R1:
ipv uni
!
interface FastEthernet0/0
ip address 123.0.0.1 255.255.255.0
ipv6 enable
ospfv3 1 ipv4 area 0
no shut
!
router ospfv3 1
!
address-family ipv4 unicast
router-id 1.1.1.1
exit-address-family
R2:
ipv uni
!
interface FastEthernet0/0
ip address 123.0.0.2 255.255.255.0
ipv6 enable
ospfv3 1 ipv4 area 0
no shut
!
interface Serial1/0
ip address 24.0.0.2 255.255.255.0
ipv6 enable
ospfv3 1 ipv4 area 1
no shut
!
router ospfv3 1
!
address-family ipv4 unicast
router-id 2.2.2.2
exit-address-family
R3:
ipv uni
!
interface FastEthernet0/0
ip address 123.0.0.3 255.255.255.0
ipv6 enable
ospfv3 1 ipv4 area 0
no shut
!
interface Serial1/0
ip address 34.0.0.3 255.255.255.0
ipv6 enable
ospfv3 1 ipv4 area 1
no shut
!
router ospfv3 1
!
address-family ipv4 unicast
router-id 3.3.3.3
exit-address-family
R4:
ipv uni
!
interface Loopback0
ip address 4.4.4.4 255.255.255.0
!
interface Serial1/0
ip address 24.0.0.4 255.255.255.0
ipv6 enable
ospfv3 1 ipv4 area 1
no shut
!
interface Serial1/1
ip address 34.0.0.4 255.255.255.0
ipv6 enable
ospfv3 1 ipv4 area 1
no shut
!
router ospfv3 1
router-id 4.4.4.4
!
address-family ipv4 unicast
redistribute connected route-map CONNECTED
area 1 nssa
exit-address-family
!
route-map CONNECTED permit 10
match interface Loopback0
Area 1 an NSSA.
R2 and R3 are ABRs NSSA.
R4 is ASBR NSSA and redistributes the prefix 4.4.4.0/24 into NSSA:
We can see below that R4 creates LSA Type 7 for the prefix 4.4.4.0/24:
R4#show ospfv3 database nssa-external
OSPFv3 1 address-family ipv4 (router-id 4.4.4.4)
Type-7 AS External Link States (Area 1)
LS age: 63
LS Type: AS External Link
Link State ID: 1
Advertising Router: 4.4.4.4
LS Seq Number: 80000001
Checksum: 0x6148
Length: 48
Prefix Address: 4.4.4.0
Prefix Length: 24, Options: P
Metric Type: 2 (Larger than any link state path)
Metric: 20
Forward Address: 34.0.0.4
R4#
From RFC 3101, If there are multiple NSSA ABRs capable of performing Type 7-to-5 translation, the router advertising with higher Router ID is elected as the translator. The NSSA ABR that is no longer required to perform translation, flushes its Type 5 LSAs. In this case the RID of R2 is 2.2.2.2 and the RID of R3 is 3.3.3.3 thus R3 wins and performs the translation of LSA 7 into LSA5, the show ospv3 data ext command below shown the LSA Type 5 originated by R3:
R3#show ospfv3 database external
OSPFv3 1 address-family ipv4 (router-id 3.3.3.3)
Type-5 AS External Link States
LS age: 116
LS Type: AS External Link
Link State ID: 0
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x8315
Length: 48
Prefix Address: 4.4.4.0
Prefix Length: 24, Options: None
Metric Type: 2 (Larger than any link state path)
Metric: 20
Forward Address: 34.0.0.4
R3#
We can verify that R2 does not originate LSA Type 5 using the show ospfv3 database external self-originate command and it learns the LSA Type 5 from R3 as shown by the show ospfv3 database external adv 3.3.3.3 command:
R2#show ospfv3 database external self-originate
OSPFv3 1 address-family ipv4 (router-id 2.2.2.2)
R2#
R2#show ospfv3 database external adv 3.3.3.3
OSPFv3 1 address-family ipv4 (router-id 2.2.2.2)
Type-5 AS External Link States
LS age: 286
LS Type: AS External Link
Link State ID: 0
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x8315
Length: 48
Prefix Address: 4.4.4.0
Prefix Length: 24, Options: None
Metric Type: 2 (Larger than any link state path)
Metric: 20
Forward Address: 34.0.0.4
R2#
R3#show ospfv3 database external self-originate
OSPFv3 1 address-family ipv4 (router-id 3.3.3.3)
Type-5 AS External Link States
LS age: 217
LS Type: AS External Link
Link State ID: 0
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x8315
Length: 48
Prefix Address: 4.4.4.0
Prefix Length: 24, Options: None
Metric Type: 2 (Larger than any link state path)
Metric: 20
Forward Address: 34.0.0.4
R3#
The show ospfv3 is another way to verify which NSSA ABR is performing the translation, below the output displayed on R3 shown that it is the translator, notice line "Perform type-7/type-5 LSA translation" :
R3#show ospfv3
OSPFv3 1 address-family ipv4
Router ID 3.3.3.3
Supports NSSA (compatible with RFC 3101)
Event-log enabled, Maximum number of events: 1000, Mode: cyclic
It is an area border and autonomous system boundary router
Redistributing External Routes from,
Router is not originating router-LSAs with maximum metric
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
Minimum LSA interval 5 secs
Minimum LSA arrival 1000 msecs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Retransmission limit dc 24 non-dc 24
Number of external LSA 1. Checksum Sum 0x00791E
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Graceful restart helper support enabled
Reference bandwidth unit is 100 mbps
RFC1583 compatibility enabled
Area BACKBONE(0)
Number of interfaces in this area is 1
SPF algorithm executed 7 times
Number of LSA 12. Checksum Sum 0x065EE8
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 1
Number of interfaces in this area is 1
It is a NSSA area
Perform type-7/type-5 LSA translation
SPF algorithm executed 10 times
Number of LSA 11. Checksum Sum 0x0551F8
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
R3#
The same command show ospfv3 can be used on R2 to verify that there is no mention of the message "Perform type-7/type-5 LSA translation":
R2#show ospfv3
OSPFv3 1 address-family ipv4
Router ID 2.2.2.2
Supports NSSA (compatible with RFC 3101)
Event-log enabled, Maximum number of events: 1000, Mode: cyclic
It is an area border and autonomous system boundary router
Redistributing External Routes from,
Router is not originating router-LSAs with maximum metric
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
Minimum LSA interval 5 secs
Minimum LSA arrival 1000 msecs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Retransmission limit dc 24 non-dc 24
Number of external LSA 1. Checksum Sum 0x009704
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Graceful restart helper support enabled
Reference bandwidth unit is 100 mbps
RFC1583 compatibility enabled
Area BACKBONE(0)
Number of interfaces in this area is 1
SPF algorithm executed 12 times
Number of LSA 12. Checksum Sum 0x065EE8
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 1
Number of interfaces in this area is 1
It is a NSSA area
SPF algorithm executed 17 times
Number of LSA 11. Checksum Sum 0x057503
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
R2#
In the outputs of the show ospfv3 command displayed above on R2 and R3, we can see that the RFC 3101 is enabled as shown by the line "Supports NSSA (compatible with RFC 3101)".
We can Configure the NSSA ABR R2 as a forced NSSA LSA 7 translator using the area 1 nssa translate type7 always command, the always keyword configures an NSSA ABR as a forced NSSA LSA 7 translator:
R2(config)#router ospfv3 1
R2(config-router)#address-family ipv4 unicast
R2(config-router-af)#area 1 nssa translate type7 always
Below we can see that R2 is originating the LSA Type 5:
R2#show ospfv3 database external
OSPFv3 1 address-family ipv4 (router-id 2.2.2.2)
Type-5 AS External Link States
LS age: 31
LS Type: AS External Link
Link State ID: 2
Advertising Router: 2.2.2.2
LS Seq Number: 80000001
Checksum: 0x8D0D
Length: 48
Prefix Address: 4.4.4.0
Prefix Length: 24, Options: None
Metric Type: 2 (Larger than any link state path)
Metric: 20
Forward Address: 34.0.0.4
R2#
Let's confirm with the show ospfv3 command that R2 is the translator:
1-The line "Configured to translate Type-7 LSAs" tells us that R2 is configured as a forced NSSA
ABR translator.
2-The line "Perform type-7/type-5 LSA translation" tells us that R2 is NSSA ABR performing the
translation.
R2#show ospfv3 | incl 7
Configured to translate Type-7 LSAs
Perform type-7/type-5 LSA translation
R2#
RFC 5340 defines a new bit Nt bit (Nt stands for NSSA translation) in the Type-1 LSA for OSPFv3.
RFC 5340 section: A.4.3. Router-LSAs
Bit Nt
When set, the router is an NSSA border router that is
unconditionally translating NSSA-LSAs into AS-external-LSAs (Nt
stands for NSSA translation). Note that such routers have their
NSSATranslatorRole area configuration parameter set to Always.
(See [NSSA].)
RFC 3101 includes also the Nt Bit explained in the following option:
Appendix B: Router-LSAs
bit Nt
When set, the router is an NSSA border router that is
unconditionally translating Type-7 LSAs into Type-5 LSAs (Nt
stands for NSSA translation). Note that such routers have
their NSSATranslatorRole area configuration parameter set to
Always. (See Appendix D and Section 3.1.)
Appendix
NSSATranslatorRole
Specifies whether or not an NSSA border router will
unconditionally translate Type-7 LSAs into Type-5 LSAs. When
it is set to Always, an NSSA border router always translates
Type-7 LSAs into Type-5 LSAs regardless of the translator state
of other NSSA border routers. When it is set to Candidate, an
NSSA border router participates in the translator election
process described in Section 3.1. The default setting is
Candidate.
The LSA Type 1 originated by R2 in Area 1 shows the line "The “Unconditional NSSA translator", it indicates that the status of the NSSA ASBR router is as a forced NSSA LSA translator. This means that the Nt-Bit is set in LSA Type 1:
R2#show ospfv data router self | beg Area 1
Router Link States (Area 1)
LS age: 226
Options: (N-Bit, R-bit, DC-Bit, AF-Bit)
LS Type: Router Links
Link State ID: 0
Advertising Router: 2.2.2.2
LS Seq Number: 80000002
Checksum: 0x8006
Length: 40
Area Border Router
AS Boundary Router
Unconditional NSSA translator
Number of Links: 1
Link connected to: another Router (point-to-point)
Link Metric: 64
Local Interface ID: 4
Neighbor Interface ID: 4
Neighbor Router ID: 4.4.4.4
R2#
By default the RFC 3101 is enabled on R2, let's enable RFC 1587 using the compatible rfc1587 command:
R2(config)#router ospfv 1
R2(config-router)#address-family ipv4 uni
R2(config-router-af)#compatible rfc1587
Let's see what happen for the translation, below we can see that R3 is originating the LSA Type 5 and it is the translator:
R2#show ospfv3 database external
OSPFv3 1 address-family ipv4 (router-id 2.2.2.2)
Type-5 AS External Link States
Routing Bit Set on this LSA
LS age: 13
LS Type: AS External Link
Link State ID: 2
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x6F27
Length: 48
Prefix Address: 4.4.4.0
Prefix Length: 24, Options: None
Metric Type: 2 (Larger than any link state path)
Metric: 20
Forward Address: 34.0.0.4
R2#
Let's verify the always keyword on R2, it's clear the area 1 nssa translate type7 always command is still here:
R2#show run | s router
router ospfv3 1
!
address-family ipv4 unicast
router-id 2.2.2.2
compatible rfc1587
area 1 nssa translate type7 always
exit-address-family
R2#
Let's confirm that R3 is the translator using the show ospfv3 command:
R3#show ospfv3 | incl 7|RFC
Supports NSSA (compatible with RFC 3101)
Number of external LSA 1. Checksum Sum 0x006F27
RFC1583 compatibility enabled
SPF algorithm executed 7 times
Perform type-7/type-5 LSA translation
R3#
Why R3 is the translator even though R2 is the forced NSSA ABR translator ?
Let's see the show ospfv3 command on R2, two things we can deduce from the output:
From cisco:
1-the line "Supports NSSA (compatible with RFC 1587)" Specifies that RFC 1587 is active or that the OSPFv3 NSSA area is RFC 1587 compatible.
2-the line "Configured to translate Type-7 LSAs, inactive (RFC3101 support disabled)" Specifies that the OSPFv3 NSSA area has an ABR device configured to act as a forced translator of Type 7 LSA. However, it is inactive because RFC 3101 is disabled.
As a result, because R2 is implementing the RFC 1587 and the RFC 3101 is disabled, OSPFv3 ignores the area 1 nssa translate type7 always command, and the tie breaker is the router-id:
R2#show ospfv3
OSPFv3 1 address-family ipv4
Router ID 2.2.2.2
Supports NSSA (compatible with RFC 1587)
Event-log enabled, Maximum number of events: 1000, Mode: cyclic
It is an area border and autonomous system boundary router
Redistributing External Routes from,
Router is not originating router-LSAs with maximum metric
Initial SPF schedule delay 5000 msecs
Minimum hold time between two consecutive SPFs 10000 msecs
Maximum wait time between two consecutive SPFs 10000 msecs
Minimum LSA interval 5 secs
Minimum LSA arrival 1000 msecs
LSA group pacing timer 240 secs
Interface flood pacing timer 33 msecs
Retransmission pacing timer 66 msecs
Retransmission limit dc 24 non-dc 24
Number of external LSA 1. Checksum Sum 0x006F27
Number of areas in this router is 2. 1 normal 0 stub 1 nssa
Graceful restart helper support enabled
Reference bandwidth unit is 100 mbps
RFC1583 compatibility enabled
Area BACKBONE(0)
Number of interfaces in this area is 1
SPF algorithm executed 13 times
Number of LSA 12. Checksum Sum 0x065EE8
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
Area 1
Number of interfaces in this area is 1
It is a NSSA area
Configured to translate Type-7 LSAs, inactive (RFC3101 support disabled)
SPF algorithm executed 21 times
Number of LSA 11. Checksum Sum 0x057105
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
R2#
Let's enable RFC 1587 on R3:
R3(config)#router ospfv 1
R3(config-router)#address-family ipv4 unicast
R3(config-router-af)#compatible rfc1587
The show ospfv3 command shown that R3 is the translator because it has a higher router-id:
R3#show ospfv3 | sec type-7|RFC
Supports NSSA (compatible with RFC 1587)
RFC1583 compatibility enabled
Area BACKBONE(0)
Perform type-7/type-5 LSA translation
R3#
Therefore R3 originates LSA Type 5 as shown by the show ospfv3 database external command:
R3#show ospfv3 database external
OSPFv3 1 address-family ipv4 (router-id 3.3.3.3)
Type-5 AS External Link States
LS age: 709
LS Type: AS External Link
Link State ID: 2
Advertising Router: 3.3.3.3
LS Seq Number: 80000001
Checksum: 0x6F27
Length: 48
Prefix Address: 4.4.4.0
Prefix Length: 24, Options: None
Metric Type: 2 (Larger than any link state path)
Metric: 20
Forward Address: 34.0.0.4
R3#
Let's confirm by changing the router-id of R2 to be higher than 3.3.3.3, for example 22.22.22.22, clear the OSPFv3 process using the clear ospfv3 process command:
R2(config)#router ospfv 1
R2(config-router)#address-family ipv4 unicast
R2(config-router-af)#router-id 22.22.22.22
% OSPFv3-1-IPv4: Reload or use "clear ospfv3 process" command, for this to take effect
R2(config-router-af)#do clea ospfv3 pro
Reset selected OSPFv3 processes? [no]: y
R2(config-router-af)#
*Sep 18 08:57:51.563: %OSPFv3-5-ADJCHG: Process 1, IPv4, Nbr 1.1.1.1 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
*Sep 18 08:57:51.567: %OSPFv3-5-ADJCHG: Process 1, IPv4, Nbr 3.3.3.3 on FastEthernet0/0 from FULL to DOWN, Neighbor Down: Interface down or detached
*Sep 18 08:57:51.647: %OSPFv3-5-ADJCHG: Process 1, IPv4, Nbr 4.4.4.4 on Serial1/0 from FULL to DOWN, Neighbor Down: Interface down or detached
*Sep 18 08:57:52.375: %OSPFv3-5-ADJCHG: Process 1, IPv4, Nbr 4.4.4.4 on Serial1/0 from LOADING to FULL, Loading Done
Now R2 is the Translator because it has a higher router-id:
R2#show ospfv3 | incl 7|RFC
Supports NSSA (compatible with RFC 1587)
RFC1583 compatibility enabled
Configured to translate Type-7 LSAs, inactive (RFC3101 support disabled)
Perform type-7/type-5 LSA translation
R2#
R3#show ospfv3 | beg Area 1
Area 1
Number of interfaces in this area is 1
It is a NSSA area
SPF algorithm executed 17 times
Number of LSA 11. Checksum Sum 0x049B1A
Number of DCbitless LSA 0
Number of indication LSA 0
Number of DoNotAge LSA 0
Flood list length 0
R3#
