Thanks for the reply Tron, please see below (I emitted some details like hostname/IP).
Even running tcpdump without port specified shows no packets at all on the interface.. so it seems the link is completely dead which makes me think it must be a physical issue.
Standby_Gateway:0> cphaprob stat
Cluster Mode: Virtual System Load Sharing (Primary Up)
ID Unique Address Assigned Load State Name
1 x.x.x.x 100% ACTIVE(!) Primary_Gateway
2 (local) x.x.x.x 0% DOWN Standby_Gateway
Active PNOTEs: IAC
Last member state change event:
Event Code: CLUS-110205
State change: ACTIVE(!) -> DOWN
Reason for state change: Interface eth3-04 is down (disconnected / link down)
Event time: Mon Aug 7 13:39:34 2023
Last cluster failover event:
Transition to new ACTIVE: Member 1 -> Member 2
Reason: Available on member 1
Event time: Mon Aug 7 13:39:01 2023
Cluster failover count:
Failover counter: 7
Time of counter reset: Tue Sep 6 17:00:37 2022 (reboot)
Cluster name: Cluster
Virtual Devices Status on each Cluster Member
=============================================
ID | Weight| Primary | Standby
| | |
| | |
| | | [local]
-------+-------+-----------+-----------
2 | 10 | ACTIVE(!) | DOWN
3 | 10 | ACTIVE(!) | DOWN
---------------+-----------+-----------
Active | 2 | 0
Weight | 20 | 0
Weight (%) | 100 | 0
Legend: Init - Initializing, Active! - Active Attention
Down! - ClusterXL Inactive or Virtual System is Down
Standby_Gateway:0> cphaprob -a if
vsid 0:
------
CCP mode: Manual (Unicast)
Required interfaces: 1
Required secured interfaces: 0
Interface Name: Status:
eth1-01 UP
eth3-04 (S) DOWN (72062 secs)
S - sync, HA/LS - bond type, LM - link monitor, P - probing
Virtual cluster interfaces: 1
eth1-01 x.x.x.x
[Expert@Standby_Gateway:0]# tcpdump -nni eth3-04 port 8116
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth3-04, link-type EN10MB (Ethernet), capture size 262144 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel