OSPF NSSA

19 Jan 2023

      Hello Team,

I encountered a weird problem with OSPF. I attache scheme.png.

R1 and R2 has configured area0 via vlan1000, both has also area1 NSSA to 
R3. Simply:

-------------------------
config R1:

protocol ospf CORE_OSPF {
         tick 1;
         ipv4 {
                 import all;
                 export none;
         };
         area 0.0.0.0 {
                 interface "vlan1000" {
                         cost 2;
                         type ptp;
                         bfd;
                 };
         };

         area 0.0.0.1 {
                 nssa;
                 interface "vlan4001" {
                         type ptp;
                         bfd yes;
                 };
         };
};
R1: Bird 2.0.10
-------------------------
config R2:

protocol ospf CORE_OSPF {
         tick 1;
         ipv4 {
                 import all;
                 export none;
         };
         area 0.0.0.0 {
                 interface "vlan1000" {
                         cost 2;
                         type ptp;
                         bfd;
                 };
         };

         area 0.0.0.1 {
                 nssa;
                 interface "vlan4011" {
                         type ptp;
                         bfd yes;
                 };
         };
};

R2: Bird 2.0.11

-------------------------
config R3:

function allow_network()
         prefix set localnet;
         {
                 localnet = [ 10.0.0.0/8{24,30}];
                 ospf_metric1 = 20;
                 if net ~ localnet then
                         return true;
                 else
                         return false;
         }

filter out_connected {
         if allow_network() then
                 accept;
         else
                 reject;
}

protocol ospf CORE_OSPF {
         tick 1;
         ipv4 {
                 import all;
                 export filter out_connected;
         };
         area 0.0.0.1 {
                 nssa;
                 interface "vlan4001" {
                         cost 100;
                         type ptp;
                         bfd yes;
                 };
                 interface "vlan4011" {
                         cost 100;
                         type ptp;
                         bfd yes;
                 };
         };
};

conntected interface with 10.7.100.254/24:

# ifconfig vlan91
vlan91: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 
1500

options=4600703<RXCSUM,TXCSUM,TSO4,TSO6,LRO,RXCSUM_IPV6,TXCSUM_IPV6,NOMAP>
         ether a0:36:9f:9d:4a:4c
         inet 10.7.100.254 netmask 0xffffff00 broadcast 10.7.100.255
         groups: vlan
         vlan: 91 vlanproto: 802.1q vlanpcp: 0 parent interface: lagg0
         media: Ethernet autoselect
         status: active
         nd6 options=29<PERFORMNUD,IFDISABLED,AUTO_LINKLOCAL>

R3: Bird 2.0.11

-------------------------

In normale state, every looks good. R1 and R2 see connected subnets from 
R3 as OSPF E1 via local vlan (R1->4001, R2->4011), R3 recevied default 
route (nssa):

from R1:

BIRD 2.0.10 ready.
bird> show route for 10.7.100.254
Table master4:
10.7.100.0/24        unicast [CORE_OSPF 23:08:09.064] * E1 (150/30) 
[xx.xx.xx.xx]
         via xx.xx.92.141 on vlan4001
bird>

from R2:

BIRD 2.0.11 ready.
bird> show route for 10.7.100.254
Table master4:
10.7.100.0/24        unicast [CORE_OSPF 23:21:35.334] * E1 (150/30) 
[xx.xx.xx.xx]
         via xx.xx.92.137 on vlan4011
bird>

but when on the switch remove e.g. vlan4001 to R3 (broken L2 
connectivity), R1 still see via vlan4001 (all dead times have expired - 
configured bfd). When I set ifconfig vlan4001 down on R3 the 
announcement disappears, R1 and R2 to do not see 10.7.100.0/24. if in 
this state (vlan4001 - broken connectivity, R3: vlan4001 state down), I 
restart bird process the situation is getting better - R2 see 
10.7.100.254 via vlan4011 and R1 see 10.7.100.254 via vlan1000 (area0).

I rewrite R3 config from Bird to Quagga and there is no such things. I 
have also R4 (mikrotik) connected in a similar way (AREA2 NSSA) and also 
works fine  when I emulate L2 connectivity interrupt.
I can provide all the logs from the devices,
All nodes are FreeBSD.

Regards,
Konrad Kręciwilk