[POC] Cisco vs Juniper running OSPF w/o Backbone Area 0

As everyone knows that OSPFv2 is a standard routing protocol (http://www.ietf.org/rfc/rfc2328.txt), but not all vendors device will implement it exactly the same. Especially when the network scenario was not follow the standard design, then it might have different exceptional behavior in different vendor devices.

In order to compare the difference behavior between Cisco and Juniper. I designed a special OSPF topology just like below, so we can see Cisco and Juniper have different result of routing exchange behavior.

Cisco IOS (GNS3)

When we are using Cisco device with IOS to simulate this topology:

  • R1 will not receive any routes. But if you check the R1 OSPF database, actually, you still see that LSA type 5 was received from R2, even R2 is not an ABR(because it has no backbone area 0).
  • R2 will learn all routes because it belong to both OSPF areas.
  • R3 will only learn all routes which was belong to area 2.
R1#sh running-config
Building configuration...

 Current configuration : 1144 bytes
!
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname R1
!
boot-start-marker
boot-end-marker
!
!
ip subnet-zero
no ip icmp rate-limit unreachable
ip cef
!
!
ip tcp synwait-time 5
no ip domain-lookup
!
no mpls traffic-eng auto-bw timers frequency 0
call rsvp-sync
!
!
!
!
!
!
!
!
interface FastEthernet0/0
ip address 10.1.1.1 255.255.255.252
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet1/0
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet1/1
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
router ospf 1
log-adjacency-changes
network 1.1.1.1 0.0.0.0 area 1
network 10.1.1.0 0.0.0.3 area 1
!
ip classless
!
no ip http server
!
!
!
!
!
!
control-plane
!
!
dial-peer cor custom
!
!
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line vty 0 4
no login
!
!
end

R1#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

 Gateway of last resort is not set

      10.0.0.0/30 is subnetted, 1 subnets

C       10.1.1.0 is directly connected, FastEthernet0/0

R1#sh ip ospf database

             OSPF Router with ID (10.1.1.1) (Process ID 1)

                 Router Link States (Area 1)

 Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         882         0x80000003 0x005AA9 1
10.1.1.1        10.1.1.1        903         0x80000003 0x00CB31 1

                 Net Link States (Area 1)

 Link ID         ADV Router      Age         Seq#       Checksum
10.1.1.1        10.1.1.1        903         0x80000002 0x003ECE

                 Type-5 AS External Link States

 Link ID         ADV Router      Age         Seq#       Checksum Tag
100.100.100.0   10.1.1.6        697         0x80000002 0x003A26 0



 R2#sh run
Building configuration...

 Current configuration : 1297 bytes
!
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname R2
!
boot-start-marker
boot-end-marker
!
!
ip subnet-zero
no ip icmp rate-limit unreachable
ip cef
!
!
ip tcp synwait-time 5
no ip domain-lookup
!
no mpls traffic-eng auto-bw timers frequency 0
call rsvp-sync
!
!
!
!
!
!
!
!
interface Loopback0
ip address 2.2.2.2 255.255.255.255
no clns route-cache
!
interface FastEthernet0/0
ip address 10.1.1.2 255.255.255.252
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet0/1
ip address 10.1.1.5 255.255.255.252
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet1/0
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet1/1
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
router ospf 1
log-adjacency-changes
redistribute static subnets
network 2.2.2.2 0.0.0.0 area 2
network 10.1.1.0 0.0.0.3 area 1
network 10.1.1.4 0.0.0.3 area 2
!
ip classless
!
no ip http server
!
!
!
!
!
!
control-plane
!
!
dial-peer cor custom
!
!
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line vty 0 4
no login
!
!
end

R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

 Gateway of last resort is not set

      2.0.0.0/32 is subnetted, 1 subnets
C       2.2.2.2 is directly connected, Loopback0
     100.0.0.0/24 is subnetted, 1 subnets
O E2    100.100.100.0 [110/20] via 10.1.1.6, 00:51:05, FastEthernet0/1
     3.0.0.0/32 is subnetted, 1 subnets
O       3.3.3.3 [110/2] via 10.1.1.6, 00:51:05, FastEthernet0/1
     10.0.0.0/30 is subnetted, 2 subnets
C       10.1.1.0 is directly connected, FastEthernet0/0

C       10.1.1.4 is directly connected, FastEthernet0/1



R2#sh ip ospf database

            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         1315        0x80000003 0x005AA9 1
10.1.1.1        10.1.1.1        1338        0x80000003 0x00CB31 1

                Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
10.1.1.1        10.1.1.1        1338        0x80000002 0x003ECE

                Router Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         1315        0x80000004 0x00DC06 2
10.1.1.6        10.1.1.6        1130        0x80000005 0x00794F 2

                Net Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum
10.1.1.5        2.2.2.2         1315        0x80000002 0x00A365

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
100.100.100.0   10.1.1.6        1130        0x80000002 0x003A26 0



 R3#sh run
Building configuration...

 Current configuration : 1295 bytes
!
version 12.2
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname R3
!
boot-start-marker
boot-end-marker
!
!
ip subnet-zero
no ip icmp rate-limit unreachable
ip cef
!
!
ip tcp synwait-time 5
no ip domain-lookup
!
no mpls traffic-eng auto-bw timers frequency 0
call rsvp-sync
!
!
!
!
!
!
!
!
interface Loopback0
ip address 3.3.3.3 255.255.255.255
no clns route-cache
!
interface FastEthernet0/0
ip address 10.1.1.6 255.255.255.252
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet0/1
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet1/0
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
interface FastEthernet1/1
no ip address
shutdown
duplex auto
speed auto
no clns route-cache
!
router ospf 1
log-adjacency-changes
redistribute static subnets
network 3.3.3.3 0.0.0.0 area 2
network 10.1.1.4 0.0.0.3 area 2
!
ip classless
ip route 100.100.100.0 255.255.255.0 Null0
!
no ip http server
!
!
!
!
!
!
control-plane
!

!
dial-peer cor custom
!
!
!
!
line con 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line aux 0
exec-timeout 0 0
privilege level 15
logging synchronous
stopbits 1
line vty 0 4
no login
!
!
end

R3#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route

 Gateway of last resort is not set

      2.0.0.0/32 is subnetted, 1 subnets
O       2.2.2.2 [110/2] via 10.1.1.5, 00:52:24, FastEthernet0/0
     100.0.0.0/24 is subnetted, 1 subnets
S       100.100.100.0 is directly connected, Null0
     3.0.0.0/32 is subnetted, 1 subnets
C       3.3.3.3 is directly connected, Loopback0
     10.0.0.0/30 is subnetted, 1 subnets

C       10.1.1.4 is directly connected, FastEthernet0/0



R3# sh ip ospf database

            OSPF Router with ID (10.1.1.6) (Process ID 1)

                Router Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         1387        0x80000004 0x00DC06 2
10.1.1.6        10.1.1.6        1200        0x80000005 0x00794F 2

                Net Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum
10.1.1.5        2.2.2.2         1387        0x80000002 0x00A365

                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
100.100.100.0   10.1.1.6        1200        0x80000002 0x003A26 0


Juniper JUNOS(olive)

When we are using Juniper device with JUNOS to simulate the same topology:

  • R1 will receive all routes. Just like we still have OSPF backbone area 0.
  • R2 will learn all routes because it belong to both OSPF areas.
  • R3 will receive all routes. Just like we still have OSPF backbone area 0.

 lab# show logical-systems R1
interfaces {
    em1 {
        unit 12 {
            vlan-id 12;
            family inet {
                address 10.1.1.1/30;
            }
        }
    }
    lo0 {
        unit 1 {
            family inet {
                address 1.1.1.1/32;
            }
        }
    }
}
protocols {
    ospf {
        area 0.0.0.1 {
            interface em1.12;
            interface lo0.1;
        }
    }
}



lab# run show route logical-system R1

inet.0: 8 destinations, 8 routes (8 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

1.1.1.1/32         *[Direct/0] 02:19:11
                    > via lo0.1
2.2.2.2/32         *[OSPF/10] 00:03:01, metric 1
                    > to 10.1.1.2 via em1.12
3.3.3.3/32         *[OSPF/10] 00:03:01, metric 2
                    > to 10.1.1.2 via em1.12
10.1.1.0/30        *[Direct/0] 00:03:46
                    > via em1.12
10.1.1.1/32        *[Local/0] 00:03:46
                      Local via em1.12
10.1.1.4/30        *[OSPF/10] 00:03:01, metric 2
                    > to 10.1.1.2 via em1.12
100.100.100.0/24   *[OSPF/150] 00:03:01, metric 0, tag 0
                    > to 10.1.1.2 via em1.12
224.0.0.5/32       *[OSPF/10] 02:13:34, metric 1
                      MultiRecv


[edit]
lab# run show ospf database detail logical-system R1

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router  *1.1.1.1          1.1.1.1          0x8000001b   206  0x22 0x2eb3  48
  bits 0x0, link count 2
  id 10.1.1.2, data 10.1.1.1, Type Transit (2)
    Topology count: 0, Default metric: 1
  id 1.1.1.1, data 255.255.255.255, Type Stub (3)
    Topology count: 0, Default metric: 0
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.2
      Metric: 1, Bidirectional
Router   2.2.2.2          2.2.2.2          0x8000001b   207  0x22 0x31ba  36
  bits 0x1, link count 1
  id 10.1.1.2, data 10.1.1.2, Type Transit (2)
    Topology count: 0, Default metric: 1
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.2
      Metric: 1, Bidirectional
Network  10.1.1.2         2.2.2.2          0x80000004   207  0x22 0x1404  32
  mask 255.255.255.252
  attached router 2.2.2.2
  attached router 1.1.1.1
  Topology default (ID 0)
    Type: Transit, Node ID: 1.1.1.1
      Metric: 0, Bidirectional
    Type: Transit, Node ID: 2.2.2.2
      Metric: 0, Bidirectional
Summary  2.2.2.2          2.2.2.2          0x80000004  2007  0x22 0xea3f  28
  mask 255.255.255.255
  Topology default (ID 0) -> Metric: 0
Summary  3.3.3.3          2.2.2.2          0x80000003   207  0x22 0xc85d  28
  mask 255.255.255.255
  Topology default (ID 0) -> Metric: 1
Summary  10.1.1.4         2.2.2.2          0x80000009   211  0x22 0x73ab  28
  mask 255.255.255.252
  Topology default (ID 0) -> Metric: 1
ASBRSum  3.3.3.3          2.2.2.2          0x80000003   207  0x22 0xba6a  28
  mask 0.0.0.0
  Topology default (ID 0) -> Metric: 1
    OSPF AS SCOPE link state database
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Extern   100.100.100.0    3.3.3.3          0x80000002  1245  0x22 0x86f1  36
  mask 255.255.255.0
  Topology default (ID 0)
    Type: 2, Metric: 0, Fwd addr: 0.0.0.0, Tag: 0.0.0.0



[edit]
lab# show logical-systems R2
interfaces {
    em2 {
        unit 12 {
            vlan-id 12;
            family inet {
                address 10.1.1.2/30;
            }
        }
        unit 23 {
            vlan-id 23;
            family inet {
                address 10.1.1.5/30;
            }
        }
    }
    lo0 {
        unit 2 {
            family inet {
                address 2.2.2.2/32;
            }
        }
    }
}
protocols {
    ospf {
        area 0.0.0.1 {
            interface em2.12;
        }
        area 0.0.0.2 {
            interface lo0.2;
            interface em2.23;
        }
    }
}



[edit]
lab# run show route logical-system R2

inet.0: 9 destinations, 9 routes (9 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

1.1.1.1/32         *[OSPF/10] 00:04:47, metric 1
                    > to 10.1.1.1 via em2.12
2.2.2.2/32         *[Direct/0] 02:20:57
                    > via lo0.2
3.3.3.3/32         *[OSPF/10] 00:04:51, metric 1
                    > to 10.1.1.6 via em2.23
10.1.1.0/30        *[Direct/0] 00:05:32
                    > via em2.12
10.1.1.2/32        *[Local/0] 00:05:32
                      Local via em2.12
10.1.1.4/30        *[Direct/0] 00:05:32
                    > via em2.23
10.1.1.5/32        *[Local/0] 00:05:32
                      Local via em2.23
100.100.100.0/24   *[OSPF/150] 00:04:51, metric 0, tag 0
                    > to 10.1.1.6 via em2.23
224.0.0.5/32       *[OSPF/10] 02:15:20, metric 1
                      MultiRecv



[edit]
lab# run show ospf database detail logical-system R2

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router   1.1.1.1          1.1.1.1          0x8000001b   255  0x22 0x2eb3  48
  bits 0x0, link count 2
  id 10.1.1.2, data 10.1.1.1, Type Transit (2)
    Topology count: 0, Default metric: 1
  id 1.1.1.1, data 255.255.255.255, Type Stub (3)
    Topology count: 0, Default metric: 0
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.2
      Metric: 1, Bidirectional
Router  *2.2.2.2          2.2.2.2          0x8000001b   254  0x22 0x31ba  36
  bits 0x1, link count 1
  id 10.1.1.2, data 10.1.1.2, Type Transit (2)
    Topology count: 0, Default metric: 1
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.2
      Metric: 1, Bidirectional
Network *10.1.1.2         2.2.2.2          0x80000004   254  0x22 0x1404  32
  mask 255.255.255.252
  attached router 2.2.2.2
  attached router 1.1.1.1
  Topology default (ID 0)
    Type: Transit, Node ID: 1.1.1.1
      Metric: 0, Bidirectional
    Type: Transit, Node ID: 2.2.2.2
      Metric: 0, Bidirectional
Summary *2.2.2.2          2.2.2.2          0x80000004  2054  0x22 0xea3f  28
  mask 255.255.255.255
  Topology default (ID 0) -> Metric: 0
Summary *3.3.3.3          2.2.2.2          0x80000003   254  0x22 0xc85d  28
  mask 255.255.255.255
  Topology default (ID 0) -> Metric: 1
Summary *10.1.1.4         2.2.2.2          0x80000009   258  0x22 0x73ab  28
  mask 255.255.255.252
  Topology default (ID 0) -> Metric: 1
ASBRSum *3.3.3.3          2.2.2.2          0x80000003   254  0x22 0xba6a  28
  mask 0.0.0.0
  Topology default (ID 0) -> Metric: 1

    OSPF database, Area 0.0.0.2
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router  *2.2.2.2          2.2.2.2          0x80000010   258  0x22 0xad2a  48
  bits 0x1, link count 2
  id 10.1.1.6, data 10.1.1.5, Type Transit (2)
    Topology count: 0, Default metric: 1
  id 2.2.2.2, data 255.255.255.255, Type Stub (3)
    Topology count: 0, Default metric: 0
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.6
      Metric: 1, Bidirectional
Router   3.3.3.3          3.3.3.3          0x80000012   259  0x22 0xc007  48
  bits 0x2, link count 2
  id 10.1.1.6, data 10.1.1.6, Type Transit (2)
    Topology count: 0, Default metric: 1
  id 3.3.3.3, data 255.255.255.255, Type Stub (3)
    Topology count: 0, Default metric: 0
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.6
      Metric: 1, Bidirectional
Network  10.1.1.6         3.3.3.3          0x80000004   259  0x22 0x22e5  32
  mask 255.255.255.252
  attached router 3.3.3.3
  attached router 2.2.2.2
  Topology default (ID 0)
    Type: Transit, Node ID: 2.2.2.2
      Metric: 0, Bidirectional
    Type: Transit, Node ID: 3.3.3.3
      Metric: 0, Bidirectional
Summary *1.1.1.1          2.2.2.2          0x80000003   254  0x22 0x2509  28
  mask 255.255.255.255
  Topology default (ID 0) -> Metric: 1
Summary *10.1.1.0         2.2.2.2          0x80000003  1721  0x22 0xa781  28
  mask 255.255.255.252
  Topology default (ID 0) -> Metric: 1
    OSPF AS SCOPE link state database
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Extern   100.100.100.0    3.3.3.3          0x80000002  1292  0x22 0x86f1  36
  mask 255.255.255.0
  Topology default (ID 0)
    Type: 2, Metric: 0, Fwd addr: 0.0.0.0, Tag: 0.0.0.0



[edit]
lab# show logical-systems R3
interfaces {
    em3 {
        unit 23 {
            vlan-id 23;
            family inet {
                address 10.1.1.6/30;
            }
        }
    }
    lo0 {
        unit 3 {
            family inet {
                address 3.3.3.3/32;
            }
        }
    }
}
protocols {
    ospf {
        export STATIC2OSPF;
        area 0.0.0.2 {
            interface em3.23;
            interface lo0.3;
        }
    }
}
policy-options {
    policy-statement STATIC2OSPF {
        from protocol static;
        then accept;
    }
}
routing-options {
    static {
        route 100.100.100.0/24 discard;
    }
}



[edit]
lab# run show route logical-system R3

inet.0: 8 destinations, 8 routes (8 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

1.1.1.1/32         *[OSPF/10] 00:05:44, metric 2
                    > to 10.1.1.5 via em3.23
2.2.2.2/32         *[OSPF/10] 00:05:49, metric 1
                    > to 10.1.1.5 via em3.23
3.3.3.3/32         *[Direct/0] 00:48:49
                    > via lo0.3
10.1.1.0/30        *[OSPF/10] 00:05:49, metric 2
                    > to 10.1.1.5 via em3.23
10.1.1.4/30        *[Direct/0] 00:06:30
                    > via em3.23
10.1.1.6/32        *[Local/0] 00:06:30
                      Local via em3.23
100.100.100.0/24   *[Static/5] 00:42:07
                      Discard
224.0.0.5/32       *[OSPF/10] 00:48:50, metric 1
                      MultiRecv



[edit]
lab# run show ospf database detail logical-system R3

    OSPF database, Area 0.0.0.2
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router   2.2.2.2          2.2.2.2          0x80000010   362  0x22 0xad2a  48
  bits 0x1, link count 2
  id 10.1.1.6, data 10.1.1.5, Type Transit (2)
    Topology count: 0, Default metric: 1
  id 2.2.2.2, data 255.255.255.255, Type Stub (3)
    Topology count: 0, Default metric: 0
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.6
      Metric: 1, Bidirectional
Router  *3.3.3.3          3.3.3.3          0x80000012   361  0x22 0xc007  48
  bits 0x2, link count 2
  id 10.1.1.6, data 10.1.1.6, Type Transit (2)
    Topology count: 0, Default metric: 1
  id 3.3.3.3, data 255.255.255.255, Type Stub (3)
    Topology count: 0, Default metric: 0
  Topology default (ID 0)
    Type: Transit, Node ID: 10.1.1.6
      Metric: 1, Bidirectional
Network *10.1.1.6         3.3.3.3          0x80000004   361  0x22 0x22e5  32
  mask 255.255.255.252
  attached router 3.3.3.3
  attached router 2.2.2.2
  Topology default (ID 0)
    Type: Transit, Node ID: 2.2.2.2
      Metric: 0, Bidirectional
    Type: Transit, Node ID: 3.3.3.3
      Metric: 0, Bidirectional
Summary  1.1.1.1          2.2.2.2          0x80000003   358  0x22 0x2509  28
  mask 255.255.255.255
  Topology default (ID 0) -> Metric: 1
Summary  10.1.1.0         2.2.2.2          0x80000003  1825  0x22 0xa781  28
  mask 255.255.255.252
  Topology default (ID 0) -> Metric: 1
    OSPF AS SCOPE link state database
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Extern  *100.100.100.0    3.3.3.3          0x80000002  1394  0x22 0x86f1  36
  mask 255.255.255.0
  Topology default (ID 0)
    Type: 2, Metric: 0, Fwd addr: 0.0.0.0, Tag: 0.0.0.0

Conclusion:

If you have such kind of IOT network design you should be aware of this to prepare some workaround for such surprise if area 0 interface was disappeared in the OSPF network(ex: the ABR uplink interface was disconnect) !

Reference:

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