bird2 doesn't negotiate with gobgp over ipv6

[Vladimir Pouzanov]

Hi!

I'm running bird 2.15.1 and I'm trying to make it talk to cilium that uses
gobgp under the hood. I can negotiate the session over ipv4 with no issues,
but due to a bug in the cilium implementation, the ipv6 routes aren't
advertised properly. The suggestion from cilium was to negotiate the
session over ipv6, but this creates issues for bird.

I have a config that looks somewhat like this:

protocol bgp {
  local port 179 as 65100;
  neighbor range 0::/0 port 179 as 65100 internal;

  dynamic name "GW6_";
  direct;
  passive;

  ipv4 {
    import all;
  };

  ipv6 {
    import all;
  };
}

protocol bgp {
  local port 179 as 65100;
  neighbor range 10.0.0.0/8 port 179 as 65100 internal;

  dynamic name "GW4_";
  direct;
  passive;

  ipv4 {
    import all;
  };

  ipv6 {
    import all;
  };
}

When I connect to bird over ipv4, gobgp sends a packet like this:

Frame 4: 154 bytes on wire (1232 bits), 154 bytes captured (1232 bits) on
interface vmbrdev, id 0
Ethernet II, Src: 22:fc:7f:47:6b:f4 (22:fc:7f:47:6b:f4), Dst:
6e:82:6c:1b:e9:95 (6e:82:6c:1b:e9:95)
Internet Protocol Version 4, Src: 10.224.129.15, Dst: 10.224.129.1
Transmission Control Protocol, Src Port: 39201, Dst Port: 179, Seq: 1, Ack:
1, Len: 88
Border Gateway Protocol - OPEN Message
    Marker: ffffffffffffffffffffffffffffffff
    Length: 88
    Type: OPEN Message (1)
    Version: 4
    My AS: 65100
    Hold Time: 90
    BGP Identifier: 10.224.129.15
    Optional Parameters Length: 59
    Optional Parameters
        Optional Parameter: Capability
            Parameter Type: Capability (2)
            Parameter Length: 57
            Capability: Route refresh capability
                Type: Route refresh capability (2)
                Length: 0
            Capability: FQDN Capability
                Type: FQDN Capability (73)
                Length: 12
                Hostname Length: 10
                Hostname: dev-master
                Domain Name Length: 0
                Domain Name:
            Capability: Unknown capability 75
                Type: Unknown (75)
                Length: 13
                Unknown: 0c476f4247502f332e32332e30
            Capability: Multiprotocol extensions capability
                Type: Multiprotocol extensions capability (1)
                Length: 4
                AFI: IPv4 (1)
                Reserved: 00
                SAFI: Unicast (1)
            Capability: Multiprotocol extensions capability
                Type: Multiprotocol extensions capability (1)
                Length: 4
                AFI: IPv6 (2)
                Reserved: 00
                SAFI: Unicast (1)
            Capability: Support for 4-octet AS number capability
                Type: Support for 4-octet AS number capability (65)
                Length: 4
                AS Number: 65100
            Capability: Extended Next Hop Encoding
                Type: Extended Next Hop Encoding (5)
                Length: 6
                AFI: IPv4 (1)
                SAFI: Unicast (1)
                Next hop AFI: IPv6 (2)

Which is followed up by OPEN from bird2 and they establish the session. The
logs say:

May 04 14:47:02 ammy bird[7755]: bgp2: Incoming connection from
10.224.129.15 (port 39201) accepted
May 04 14:47:02 ammy bird[7755]: GW4_1: Initializing
May 04 14:47:02 ammy bird[7755]: GW4_1: Starting
May 04 14:47:02 ammy bird[7755]: GW4_1: State changed to start
May 04 14:47:02 ammy bird[7755]: GW4_1: Started
May 04 14:47:02 ammy bird[7755]: GW4_1: Got
OPEN(as=65100,hold=90,id=10.224.129.15)
May 04 14:47:02 ammy bird[7755]: GW4_1: Sending
OPEN(ver=4,as=65100,hold=240,id=0ae08101)
May 04 14:47:02 ammy bird[7755]: GW4_1: Sending KEEPALIVE
May 04 14:47:02 ammy bird[7755]: GW4_1: Got KEEPALIVE
May 04 14:47:02 ammy bird[7755]: GW4_1: BGP session established

When I try to establish the connection over ipv6, gobgp sends an OPEN
that's exactly the same sans being transferred over ipv6:

Frame 15: 174 bytes on wire (1392 bits), 174 bytes captured (1392 bits) on
interface vmbrdev, id 0
Ethernet II, Src: 22:fc:7f:47:6b:f4 (22:fc:7f:47:6b:f4), Dst:
6e:82:6c:1b:e9:95 (6e:82:6c:1b:e9:95)
Internet Protocol Version 6, Src: 2a01:xxx:xxx:xxx:xxx:xxx:xxx:d930, Dst:
fd00::53
Transmission Control Protocol, Src Port: 58663, Dst Port: 179, Seq: 1, Ack:
1, Len: 88

and then bird just stalls the connection. The logs say:

May 04 14:49:17 ammy bird[7755]: bgp1: Incoming connection from
2a01:4f8:173:fe11:6f81:e7cd:2787:fb71 (port 35581) accepted
May 04 14:49:17 ammy bird[7755]: GW6_1: Initializing
May 04 14:49:17 ammy bird[7755]: GW6_1: Starting
May 04 14:49:17 ammy bird[7755]: GW6_1: State changed to start
May 04 14:49:17 ammy bird[7755]: GW6_1: Waiting for
2a01:xxx:xxx:xxx:xxx:xxx:xxx:d930 to become my neighbor

I suspect it's either a bug or a misconfiguration on the bird side, because
gobgp behaves the same in both scenarios. How do I investigate/debug this
further?
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