Multicast receivers connected through a QFX switch report packet loss, a reduced packet rate, or packets arriving out of sequence. The QFX is operating as a Layer 2 switch with IGMP snooping enabled.
The QFX forwarding state and counters were healthy. The confirmed cause was the upstream core-routing design.
· Some receivers report out-of-sequence multicast video or a reduced packet rate, while other paths remain stable.
· MAC learning, IGMP snooping, and multicast counters on the QFX are correct.
· No multicast queue drops, DDoS violations, or abnormal process utilization are seen on the QFX.
· The upstream router may report RPF events, route changes, or interface flaps.
· An aggregated Ethernet member may show receive errors. This should be checked separately and does not confirm the root cause by itself.
Example error indicators:
user@router> show interfaces <physical-member> statistics | match errors
Input errors: <non-zero>, Output errors: 0
Bit errors: <non-zero>
CRC/Align errors: <non-zero>
Carrier transitions: <non-zero>
Validate QFX Layer 2 forwarding, then check the upstream multicast-routing path. Replace the values in angle brackets with values from the network.
1. Verify MAC learning and IGMP snooping
user@switch> show ethernet-switching table | match <vlan-id>
user@switch> show igmp snooping membership
Confirm that receiver MAC addresses are learned on access ports and the upstream router MAC address is learned on the expected aggregated Ethernet interface.
2. Confirm that the stream reaches the QFX
Use a temporary input filter to count packets for one source and group:
set firewall family ethernet-switching filter MCAST-CHECK interface-specific
set firewall family ethernet-switching filter MCAST-CHECK term STREAM from ip-source-address <source-ip>/32
set firewall family ethernet-switching filter MCAST-CHECK term STREAM from ip-destination-address <group-ip>/32
set firewall family ethernet-switching filter MCAST-CHECK term STREAM then count MCAST-PKTS
set firewall family ethernet-switching filter MCAST-CHECK term STREAM then accept
set firewall family ethernet-switching filter MCAST-CHECK term DEFAULT then accept
set interfaces <ae-interface> unit 0 family ethernet-switching filter input MCAST-CHECK
Expected result
user@switch> show firewall filter MCAST-CHECK-<interface>-i
MCAST-PKTS-<interface>-i <bytes increasing> <packets increasing>
Important
Keep the final accept term in the temporary filter. Without it, unrelated traffic may be dropped. Remove the filter after testing.
3. Check both ends of every aggregated Ethernet member
user@device> show interfaces <physical-member> extensive | match "errors|CRC|carrier|flap"
user@device> show interfaces diagnostics optics <physical-member>
user@device> clear interfaces statistics <physical-member>
Clear the counters and check whether errors return. If they do, clean, reseat, or replace the affected optic or fiber path.
4. Correct the upstream routing path
Check upstream interface flaps, RPF errors, and route changes. Confirm that the route toward the multicast source uses the expected RPF interface. In this case, moving the receivers to the correct core hub resolved the issue.
Resolution
The permanent fix was applied by the customer in the upstream core-routing design. No QFX software or hardware change was required.