Cease/Connection collision resolution when down port and admindown bgp peer at the same time

[wangdan1323]

Description

 port A1------port B1
 port A2------port B2

A：port A1：100.0.0.1/24 100::1/64
port A2：200.0.0.1/24 200::1/64

B: port B1：100.0.0.2/24 100::2/64
port B2：200.0.0.2/24 200::2/64

A：
router bgp 53
bgp router-id 1.1.1.53
no bgp ebgp-requires-policy
no bgp default ipv4-unicast
timers bgp 10 30
neighbor 100.0.0.2 remote-as 55
neighbor 100.0.0.2 description connect_to_ceshiyi
neighbor 100.0.0.2 advertisement-interval 0
neighbor 100.0.0.2 timers 10 30
neighbor 100.0.0.2 timers connect 3
neighbor 200.0.0.2 remote-as 55
neighbor 200.0.0.2 description connect_to_ceshiyi
neighbor 200.0.0.2 advertisement-interval 0
neighbor 200.0.0.2 timers 10 30
neighbor 200.0.0.2 timers connect 3
neighbor 100::2 remote-as 55
neighbor 100::2 description connect_to_ceshiyi
neighbor 100::2 advertisement-interval 0
neighbor 100::2 timers 10 30
neighbor 100::2 timers connect 3
neighbor 200::2 remote-as 55
neighbor 200::2 description connect_to_ceshiyi
neighbor 200::2 advertisement-interval 0
neighbor 200::2 timers 10 30
neighbor 200::2 timers connect 3
!
address-family ipv4 unicast
neighbor 100.0.0.2 activate
neighbor 200.0.0.2 activate
exit-address-family
!
address-family ipv6 unicast
neighbor 100::2 activate
neighbor 200::2 activate
exit-address-family

B：
router bgp 55
bgp router-id 1.1.1.55
no bgp ebgp-requires-policy
no bgp default ipv4-unicast
timers bgp 10 30
neighbor 100.0.0.1 remote-as 53
neighbor 100.0.0.1 description connect_to_ceshiyi
neighbor 100.0.0.1 advertisement-interval 0
neighbor 100.0.0.1 timers 10 30
neighbor 100.0.0.1 timers connect 3
neighbor 200.0.0.1 remote-as 53
neighbor 200.0.0.1 description connect_to_ceshiyi
neighbor 200.0.0.1 advertisement-interval 0
neighbor 200.0.0.1 timers 10 30
neighbor 200.0.0.1 timers connect 3
neighbor 100::1 remote-as 53
neighbor 100::1 description connect_to_ceshiyi
neighbor 100::1 advertisement-interval 0
neighbor 100::1 timers 10 30
neighbor 100::1 timers connect 3
neighbor 200::1 remote-as 53
neighbor 200::1 description connect_to_ceshiyi
neighbor 200::1 advertisement-interval 0
neighbor 200::1 timers 10 30
neighbor 200::1 timers connect 3
!
address-family ipv4 unicast
neighbor 100.0.0.1 activate
neighbor 200.0.0.1 activate
exit-address-family
!
address-family ipv6 unicast
neighbor 100::1 activate
neighbor 200::1 activate
exit-address-family

Reproduction steps：

1 down port A1
2 neighbor 200.0.0.2 shutdown
3 neighbor 200::2 shutdown

4 up port A1
5 undo neighbor 200.0.0.2 shutdown
6 undo neighbor 200::2 shutdown

result：
BGP neighbor is 200::2, remote AS 55, local AS 53, external link
Description: connect_to_ceshiyi
Hostname: sonic
BGP version 4, remote router ID 1.1.1.55, local router ID 1.1.1.53
BGP state = Idle
Last read 00:16:04, Last write 00:00:18
Hold time is 30, keepalive interval is 10 seconds
Configured hold time is 30, keepalive interval is 10 seconds
Graceful restart information:
Local GR Mode: Helper*
Remote GR Mode: NotApplicable
R bit: False
Timers:
Configured Restart Time(sec): 120
Received Restart Time(sec): 120
IPv6 Unicast:
F bit: False
End-of-RIB sent: No
End-of-RIB sent after update: No
End-of-RIB received: No
Timers:
Configured Stale Path Time(sec): 360
Message statistics:
Inq depth is 0
Outq depth is 0
Sent Rcvd
Opens: 32 30
Notifications: 12 48
Updates: 6 6
Keepalives: 97 74
Route Refresh: 0 0
Capability: 0 0
Total: 147 158
Minimum time between advertisement runs is 0 seconds

For address family: IPv6 Unicast
Not part of any update group
Community attribute sent to this neighbor(all)
0 accepted prefixes
Maximum prefixes allowed 40000 (warning-only)
Threshold for warning message 80%

Connections established 6; dropped 6
Last reset 00:15:54, Notification received (Cease/Connection collision resolution)
Local host: 200::1, Local port: 50312
Foreign host: 200::2, Foreign port: 179
Nexthop: 200.0.0.1
Nexthop global: 200::1
Nexthop local: fe80::9a19:2cff:fe65:4780
BGP connection: shared network
BGP Connect Retry Timer in Seconds: 3
Next start timer due in 13 seconds
Read thread: off Write thread: off FD used: -1

Version

8.5

How to reproduce

Reproduction steps：

1 down port A1
2 neighbor 200.0.0.2 shutdown
3 neighbor 200::2 shutdown

4 up port A1
5 undo neighbor 200.0.0.2 shutdown
6 undo neighbor 200::2 shutdown

Expected behavior

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd PfxSnt
100::2 4 55 235 241 0 0 0 00:18:54 0 0
200::2 4 55 164 151 0 0 0 00:19:02 0 0

Actual behavior

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd PfxSnt
100::2 4 55 235 241 0 0 0 00:18:54 0 0
200::2 4 55 164 151 0 0 0 00:19:02 Idle 0

BGP neighbor is 200::2, remote AS 55, local AS 53, external link
Description: connect_to_ceshiyi
Hostname: sonic
BGP version 4, remote router ID 1.1.1.55, local router ID 1.1.1.53
BGP state = Idle
Last read 00:16:04, Last write 00:00:18
Hold time is 30, keepalive interval is 10 seconds
Configured hold time is 30, keepalive interval is 10 seconds
Graceful restart information:
Local GR Mode: Helper*
Remote GR Mode: NotApplicable
R bit: False
Timers:
Configured Restart Time(sec): 120
Received Restart Time(sec): 120
IPv6 Unicast:
F bit: False
End-of-RIB sent: No
End-of-RIB sent after update: No
End-of-RIB received: No
Timers:
Configured Stale Path Time(sec): 360
Message statistics:
Inq depth is 0
Outq depth is 0
Sent Rcvd
Opens: 32 30
Notifications: 12 48
Updates: 6 6
Keepalives: 97 74
Route Refresh: 0 0
Capability: 0 0
Total: 147 158
Minimum time between advertisement runs is 0 seconds

For address family: IPv6 Unicast
Not part of any update group
Community attribute sent to this neighbor(all)
0 accepted prefixes
Maximum prefixes allowed 40000 (warning-only)
Threshold for warning message 80%

Connections established 6; dropped 6
Last reset 00:15:54, Notification received (Cease/Connection collision resolution)
Local host: 200::1, Local port: 50312
Foreign host: 200::2, Foreign port: 179
Nexthop: 200.0.0.1
Nexthop global: 200::1
Nexthop local: fe80::9a19:2cff:fe65:4780
BGP connection: shared network
BGP Connect Retry Timer in Seconds: 3
Next start timer due in 13 seconds
Read thread: off Write thread: off FD used: -1

Additional context

No response

Checklist

• I have searched the open issues for this bug.
• I have not included sensitive information in this report.

[ton31337]

That's normal and the session should be up eventually. This is due to a fast transition.

[wangdan1323]

There is a probability that some v6 sessions will eventually fail to come up.
We see some unexpected log printing：
100.0.0.2 [FSM] Timer (routeadv timer expire)
send End-of-RIB for IPv4 Unicast to 100.0.0.2
Rx Intf address add VRF 0 IF Ethernet3 addr fe80::9a19:2cff:fe65:4780/64
100::2 [FSM] TCP_connection_open (Connect->OpenSent), fd 22
100::2 open active, local address 200::1
100::2 Sending hostname cap with hn = sonic, dn = (null)
[BGP_GR] Sending helper Capability for Peer 💯:2 :
100::2 sending OPEN, version 4, my as 53, holdtime 30, id 1.1.1.53
bgp_fsm_change_status : vrf default(0), Status: OpenSent established_peers 1

[wangdan1323]

port A1------port B1
port A2------port B2
A：port A1：100.0.0.1/24 100::1/64
port A2：200.0.0.1/24 200::1/64

B: port B1：100.0.0.2/24 100::2/64
port B2：200.0.0.2/24 200::2/64

1 down port A1
2 neighbor 200.0.0.2 shutdown
3 neighbor 200::2 shutdown
4 up port A1

BGP neighbor is 200::1, remote AS 53, local AS 55, external link
Description: connect_to_ceshiyi
Hostname: sonic
BGP version 4, remote router ID 1.1.1.53, local router ID 1.1.1.55
BGP state = Established, up for 00:01:22
Last read 00:00:02, Last write 00:00:02
Hold time is 30, keepalive interval is 10 seconds
Configured hold time is 30, keepalive interval is 10 seconds
Neighbor capabilities:
4 Byte AS: advertised and received
AddPath:
IPv6 Unicast: RX advertised IPv6 Unicast and received
Route refresh: advertised and received(old & new)
Address Family IPv6 Unicast: advertised and received
Hostname Capability: advertised (name: sonic,domain name: n/a) received (name: sonic,domain name: n/a)
Graceful Restart Capability: advertised and received
Remote Restart timer is 120 seconds
Address families by peer:
none
Graceful restart information:
End-of-RIB send: IPv6 Unicast
End-of-RIB received: IPv6 Unicast
Local GR Mode: Helper*
Remote GR Mode: Helper
R bit: False
Timers:
Configured Restart Time(sec): 120
Received Restart Time(sec): 120
IPv6 Unicast:
F bit: False
End-of-RIB sent: Yes
End-of-RIB sent after update: Yes
End-of-RIB received: Yes
Timers:
Configured Stale Path Time(sec): 360
Message statistics:
Inq depth is 0
Outq depth is 0
Sent Rcvd
Opens: 15 5
Notifications: 0 2
Updates: 5 5
Keepalives: 1300 1297
Route Refresh: 0 0
Capability: 0 0
Total: 1320 1309
Minimum time between advertisement runs is 0 seconds

For address family: IPv6 Unicast
Update group 11, subgroup 11
Packet Queue length 0
Community attribute sent to this neighbor(all)
0 accepted prefixes
Maximum prefixes allowed 40000 (warning-only)
Threshold for warning message 80%

Connections established 5; dropped 4
Last reset 00:01:45, No AFI/SAFI activated for peer
Local host: 100::2, Local port: 179
Foreign host: 200::1, Foreign port: 34718
Nexthop: 100.0.0.2
Nexthop global: 100::2
Nexthop local: fe80::fa8e:a1ff:feb8:4720
BGP connection: shared network
BGP Connect Retry Timer in Seconds: 3
Estimated round trip time: 2 ms
Read thread: on Write thread: on FD used: 29