Symptom
Multicast packets under a certain sizes are able to traverse the network but not others.
Conditions
Using C9k (excluding C9500H and C9600 thanks to CSCvu87973 fix)
C9300 recieves a fragmented Multicast packet
Packet needs to be further fragmented on C9k to traverse the outbound interface
Workaround
Lower MTU of traffic further on the previous device (or source) to fragment below the current MTU restriction for the C9k outbound interface.
Further Problem Description
Can validate these drops by checking the ASIC drops:
show plat hard fed sw act fwd drop ex | i MTU_FAIL_DROP_BRIDGED_IP_ROUTED
0 0 MTU_FAIL_DROP_BRIDGED_IP_ROUTED 0 1 1
0 1 MTU_FAIL_DROP_BRIDGED_IP_ROUTED 0 0 0
It is also noticed this issue isn't seen on the first multicast packet as the (S,G) hasn't been established and needs to be processed by the CPU. Once the (S,G) is created, further packets are dropped in hardware.
This issue is only impacting Multicast fragment packets, Unicast packets are punted to the CPU for further fragmentation as intended.
