ABR sets E-bit (and B-bit) in router LSA

[Kenth Eriksson]

I have a setup as in the attached drawing. I can see that the bird ABR node (R2) sets the E-bit and the B-bit in the router LSA. The B-bit seems correct as it is the ABR, but it is not an ASBR. 

Below is a tcpdump captured on R1

Frame 11347: 124 bytes on wire (992 bits), 124 bytes captured (992 bits)
Linux cooked capture v2
PPP-over-Ethernet Session
Point-to-Point Protocol
Internet Protocol Version 4, Src: 10.210.138.69, Dst: 224.0.0.5
Open Shortest Path First
    OSPF Header
        Version: 2
        Message Type: LS Update (4)
        Packet Length: 76
        Source OSPF Router: 10.210.138.69
        Area ID: 0.0.0.0 (Backbone)
        Checksum: 0x9d61 [correct]
        Auth Type: Null (0)
        Auth Data (none): 0000000000000000
    LS Update Packet
        Number of LSAs: 1
        LSA-type 1 (Router-LSA), len 48
            .000 0000 0000 0001 = LS Age (seconds): 1
            0... .... .... .... = Do Not Age Flag: 0
            Options: 0x42, O, (E) External Routing
                0... .... = DN: Not set
                .1.. .... = O: Set
                ..0. .... = (DC) Demand Circuits: Not supported
                ...0 .... = (L) LLS Data block: Not Present
                .... 0... = (N) NSSA: Not supported
                .... .0.. = (MC) Multicast: Not capable
                .... ..1. = (E) External Routing: Capable
                .... ...0 = (MT) Multi-Topology Routing: No
            LS Type: Router-LSA (1)
            Link State ID: 10.210.138.69
            Advertising Router: 10.210.138.69
            Sequence Number: 0x80000075
            Checksum: 0x180f
            Length: 48
            Flags: 0x03, (E) AS boundary router, (B) Area border router
                0... .... = (H) flag: No
                ...0 .... = (N) flag: No
                .... 0... = (W) Wild-card multicast receiver: No
                .... .0.. = (V) Virtual link endpoint: No
                .... ..1. = (E) AS boundary router: Yes
                .... ...1 = (B) Area border router: Yes
            Number of Links: 2
            Type: Stub     ID: 10.210.138.69   Data: 255.255.255.255 Metric: 0
            Type: PTP      ID: 10.210.138.66   Data: 10.210.138.69   Metric: 10

The Cisco router sees these bird routers as ASBR routers as well

R3-Cisco>show ip ospf border-routers 

            OSPF Router with ID (10.210.138.65) (Process ID 1)


		Base Topology (MTID 0)

Internal Router Routing Table
Codes: i - Intra-area route, I - Inter-area route

i 10.210.138.66 [1] via 10.210.138.66, GigabitEthernet0/0/1, ASBR, Area 0.0.0.0, SPF 77
i 10.210.138.69 [11] via 10.210.138.66, GigabitEthernet0/0/1, ABR/ASBR, Area 0.0.0.0, SPF 77
I 10.210.138.73 [21] via 10.210.138.66, GigabitEthernet0/0/1, ASBR, Area 0.0.0.0, SPF 77
R3-Cisco>


 R3-Cisco>show ip ospf database 

            OSPF Router with ID (10.210.138.65) (Process ID 1)

		Router Link States (Area 0.0.0.0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
10.210.138.65   10.210.138.65   870         0x800000DE 0x0091B0 2
10.210.138.66   10.210.138.66   828         0x800000AC 0x00DBB2 3
10.210.138.69   10.210.138.69   828         0x8000009F 0x00C339 2

		Net Link States (Area 0.0.0.0)

Link ID         ADV Router      Age         Seq#       Checksum
10.210.138.65   10.210.138.65   870         0x80000035 0x003F26

		Summary Net Link States (Area 0.0.0.0)

Link ID         ADV Router      Age         Seq#       Checksum
10.210.138.73   10.210.138.69   591         0x8000002D 0x002465

		Summary ASB Link States (Area 0.0.0.0)

Link ID         ADV Router      Age         Seq#       Checksum
10.210.138.73   10.210.138.69   591         0x8000002D 0x001672

		Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
0.0.0.0         10.210.138.65   1650        0x80000034 0x004EA1 1
R3-Cisco>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ospf.png
Type: image/png
Size: 19285 bytes
Desc: ospf.png
URL: <http://trubka.network.cz/pipermail/bird-users/attachments/20230127/4ab5f686/attachment.png>