A router running Junos Evolved is seeing an issue with BGP neighbor stability over IPv6 when there is an influx off TTL=1 traffic to the router.

For example, DDoS kicks in for TTL=1 indicating an increase in traffic with that time to live:

user@router> show ddos-protection protocols statistics detail
Packet types: 86, Received traffic: 26, Currently violated: 0
...

Protocol Group: TTL

 Packet type: aggregate (Aggregate for all TTL exception traffic)
  System-wide information:
   Aggregate bandwidth is no longer being violated
    Last violation started at: 2024-01-06 14:16:25 UTC
    Last violation ended at:  2024-01-23 16:00:24 UTC
    Duration of last violation: 2w3d 01:43 Number of violations: 1048
   Received: 416047021      Arrival rate:   320 pps
   Dropped:  65604914      Max arrival rate: 175273 pps
  Routing Engine information:
   Aggregate policer is no longer being violated
    Last violation started at: 2024-01-06 14:16:25 UTC
    Last violation ended at:  2024-01-06 14:16:25 UTC
    Duration of last violation: 00:00:00 Number of violations: 2
   Received: 137064858      Arrival rate:   62 pps
   Dropped:  2          Max arrival rate: 391 pps
    Dropped by individual policers: 0
    Dropped by aggregate policer:  2
  FPC slot 0 information:
   Aggregate policer is no longer being violated
    Last violation started at: 2024-01-23 05:34:20 UTC
    Last violation ended at:  2024-01-23 16:00:24 UTC
    Duration of last violation: 10:26:04 Number of violations: 1046
   Received: 416047021      Arrival rate:   320 pps
   Dropped:  65604912      Max arrival rate: 175273 pps
    Dropped by individual policers: 0
    Dropped by aggregate policer:  65604912
    Dropped by flow suppression:  0

When that trafifc is present, IPv6 BGP sessions flap...note the sessions in OpenSent or OpenConfirm:

user@router> show bgp summary | match fc00:668:0:3
fc00:668:0:3::1030:52 42459 0 0 0 0 2w6d 12:10:06 Active
fc00:668:0:3::1030:62 44814 8 492 177342 419 1:28 Establ
fc00:668:0:3::1030:92 31042 0 0 0 391 37 OpenSent
fc00:668:0:3:ffff:0:8d88:65aa 13335 16 332 176489 437 8 Establ
fc00:668:0:3:ffff:0:d5fe:d946 60447 0 0 0 0 2w6d 12:10:06 Connect
fc00:668:0:3:ffff:1:0:616 32934 6 134 0 422 17 Establ
fc00:668:0:3:ffff:1:0:61a 32934 7 147 0 433 44 Establ
fc00:668:0:3:ffff:1:0:1852 60068 1 1 0 421 2:44 OpenConfirm
fc00:668:0:3:ffff:1:0:21fe 29049 2 0 0 416 51 Active
fc00:668:0:3:ffff:1:0:233a 396998 0 0 0 0 2w6d 12:10:06 Idle

Or, the messages log is full of neighbor state change logs:

user@router> show log messages| match holdtime | last 10

Jan 23 14:56:37 router rpd[11094]: RPD_BGP_NEIGHBOR_STATE_CHANGED: BGP peer fc00:501b:100:1a::1 (External AS 65000) changed state from Established to Idle (event HoldTime) (instance master)
Jan 23 14:56:37 router rpd[11094]: bgp_io_mgmt_cb:3032: NOTIFICATION sent to fc00:501b:100:1a::1 (External AS 65000): code 4 (Hold Timer Expired Error), Reason: holdtime expired for fc00:501b:100:1a::1 (External AS 65000), socket buffer sndcc: 1659 rcvcc: 0, hold timer 90s, hold timer remain 0s, last sent 1s, TCP port (local 58488, remote 179)
Jan 23 14:57:35 router rpd[11094]: RPD_BGP_NEIGHBOR_STATE_CHANGED: BGP peer fc00:41a8:f00:2::69 (External AS 65001) changed state from Established to Idle (event HoldTime) (instance master)
Jan 23 14:57:35 router rpd[11094]: bgp_io_mgmt_cb:3032: NOTIFICATION sent to fc00:41a8:f00:2::69 (External AS 65001): code 4 (Hold Timer Expired Error), Reason: holdtime expired for fc00:41a8:f00:2::69 (External AS 65001), socket buffer sndcc: 32240 rcvcc: 0, hold timer 90s, hold timer remain 0s, last sent 4s, TCP port (local 49632, remote 179)
Jan 23 14:58:08 router rpd[11094]: RPD_BGP_NEIGHBOR_STATE_CHANGED: BGP peer fc00:668:0:3::1030:62 (External AS 65002) changed state from Established to Idle (event HoldTime) (instance master)
Jan 23 14:58:08 router rpd[11094]: bgp_io_mgmt_cb:3032: NOTIFICATION sent to fc00:668:0:3::1030:62 (External AS 65002): code 4 (Hold Timer Expired Error), Reason: holdtime expired for fc00:668:0:3::1030:62 (External AS 65002), socket buffer sndcc: 26752 rcvcc: 0, hold timer 90s, hold timer remain 0s, last sent 8s, TCP port (local 38340, remote 179)

IPv6 BGP Neighbor instability when there is an influx of TTL=1 traffic to the router

This problem is tied to PR1732443:
 

https://prsearch.juniper.net/PR1732443
 

BGP IPv6 packets are incorrectly being placed within the same queue as TTL=1 packets instead of the L3 High Priority Queue where they should be, leading to the neighbor instability.

With the fix within the PR, the correct queue is used.