The 'area area-id nssa no-redistribution' OSPF Router Subcommand

The no-redistribution keyword is being used in situations where there is no need to inject external routes into an NSSA as Type-7 LSAs, eg: when an NSSA ASBR is also an NSSA ABR.

Below shows the routing table and OSPF LSDB on RT2 before implementing the no-redistribution keyword on RT1:

RT2#sh ip route

Gateway of last resort is 10.10.10.1 to network 0.0.0.0

     172.16.0.0/32 is subnetted, 1 subnets
O N2    172.16.1.1 [110/20] via 10.10.10.1, 00:00:10, Serial0/0
     10.0.0.0/30 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, Serial0/0
O*IA 0.0.0.0/0 [110/65] via 10.10.10.1, 00:00:12, Serial0/0
RT2#
RT2#sh ip ospf database

            OSPF Router with ID (2.2.2.2) (Process ID 100)

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         17          0x80000002 0x006EE1 2
2.2.2.2         2.2.2.2         20          0x80000001 0x000748 2

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         1.1.1.1         21          0x80000001 0x001B17

                Type-7 AS External Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Tag
172.16.1.1      1.1.1.1         15          0x80000001 0x0013C8 0
RT2#
RT2#debug ip routing
IP routing debugging is on
RT2#

Below shows the configuration implemented on RT1 as well as the routing table and OSPF LSDB on RT2 after implemented the no-redistribution keyword on RT1:

RT1#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
RT1(config)#router ospf 100
RT1(config-router)#area 1 nssa no-redistribution
RT1(config-router)#do sh run | b router ospf
router ospf 100
 router-id 1.1.1.1
 log-adjacency-changes
 area 1 nssa no-redistribution no-summary
 redistribute connected subnets
 network 10.10.10.1 0.0.0.0 area 1
 network 192.168.1.1 0.0.0.0 area 0
!
======================================================================
RT2#
00:00:42: RT: del 0.0.0.0 via 10.10.10.1, ospf metric [110/65]
00:00:42: RT: delete network route to 0.0.0.0
00:00:42: RT: NET-RED 0.0.0.0/0
00:00:42: RT: NET-RED 0.0.0.0/0
00:00:43: RT: del 172.16.1.1/32 via 10.10.10.1, ospf metric [110/20]
00:00:43: RT: delete subnet route to 172.16.1.1/32
00:00:43: RT: NET-RED 172.16.1.1/32
00:00:43: RT: delete network route to 172.16.0.0
00:00:43: RT: NET-RED 172.16.0.0/16
00:00:47: RT: add 0.0.0.0/0 via 10.10.10.1, ospf metric [110/65]
00:00:47: RT: NET-RED 0.0.0.0/0
00:00:47: RT: default path is now 0.0.0.0 via 10.10.10.1
00:00:47: RT: new default network 0.0.0.0
00:00:47: RT: NET-RED 0.0.0.0/0
RT2#
RT2#sh ip route

Gateway of last resort is 10.10.10.1 to network 0.0.0.0

     10.0.0.0/30 is subnetted, 1 subnets
C       10.10.10.0 is directly connected, Serial0/0
O*IA 0.0.0.0/0 [110/65] via 10.10.10.1, 00:00:04, Serial0/0
RT2#
RT2#sh ip ospf database

            OSPF Router with ID (2.2.2.2) (Process ID 100)

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         46          0x80000002 0x006EE1 2
2.2.2.2         2.2.2.2         50          0x80000001 0x000748 2

                Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         1.1.1.1         6           0x80000002 0x001918
RT2#

Note: There was a network interruption (~ 5 seconds) upon the default route when implementing the no-redistribution keyword on RT1 due to the route re-advertisement process of RT1 and the route removal and insertion process on RT2.