This article explains the VCP port flapping issue and troubleshooting steps in virtual-chassis setup
root@userA> show virtual-chassis status
Virtual Chassis ID: 3cb7.xxxx.xxxx
Virtual Chassis Mode: Enabled
Mstr Mixed Route Neighbor List
Member ID Status Serial No Model prio Role Mode Mode ID Interface
0 (FPC 0) Prsnt Vxxxxxxxxx9 qfx5100 255 Master* N VC 1 vcp-255/0/99
1 (FPC 1) Prsnt Vxxxxxxxxxx0 qfx5100 150 Backup N VC 0 vcp-255/0/102
During VCP port flapping issue, we will notice interface flaps and carrier transaction counter increase happening. It will cause instability in the network by compromising the redundancy of VCP links and it may also cause traffic drops in the network.Sample Output During Issue State:Physical interface: vcp-255/0/102, Enabled, Physical link is Up Interface index: 129, SNMP ifIndex: 333, Generation: 132 Type: 105, Link-level type: Virtual-Chassis-Interface, MTU: 1514, Clocking: Unspecified, Speed: 40000mbps Device flags : Present Running Link type : Full-Duplex Link flags : None Physical info : Unspecified Hold-times : Up 0 ms, Down 0 ms Current address: Unspecified, Hardware address: Unspecified Alternate link address: Unspecified Last flapped : 2023-06-16 02:21:44 UTC (00:00:19 ago) Statistics last cleared: Never Traffic statistics: Input bytes : 32978346331 49073744 bps Output bytes : 18019401405 4068264 bps Input packets: 62689349 7163 pps Output packets: 24571394 2281 pps IPv6 transit statistics: Input bytes : 0 Output bytes : 0 Input packets: 0 Output packets: 0 Input errors: Errors: 1030, Drops: 0, Framing errors: 1030, Runts: 0, Giants: 0, Bucket drops: 0, Policed discards: 0, Resource errors: 0 Output errors: Carrier transitions: 667, Errors: 0, Drops: 0, MTU errors: 0, Resource errors: 0, Bucket drops: 0
> Interface will keep on flapping in every 2-3 mins
Carrier transitions means the number of times that the interface has gone from down to up. This number does not normally increment quickly; increasing only when the cable is unplugged, the far-end system is powered down and then up, or another issue occurs. If the number of carrier transitions increments quickly (perhaps once every 10 seconds), the cable, far-end system, PIC (Physical Interface Cards) or PIM (Physical Interface Module) is malfunctioning.Recovery:1. Replace QSFP module with any working QSFP
2. If in case it still behaves same, then replace VCP cable
3. For more details, refer below KB article, it will cover the other troubleshooting aspects of virtual-chassis issues:https://supportportal.juniper.net/s/article/EX-QFX-Resolution-Guide-Troubleshoot-Virtual-Chassis-VC