Strange stuff happens when you go over 1000 IGMP snooping group on a UCS fabric interconnect. Cisco UCS 6100 Series Fabric Interconnect supports up to 1000 IGMP snooping groups and Cisco UCS 6200 Series Fabric Interconnect supports up to 4000 IGMP snooping groups. Here’s how to check if you’ve taken your vxlan to the limit as vxlan relies on IGMP snooping groups to keep chatter down to a minimum on your switch.
# use the vmk interface with vxlan running on it. I used 1 in this example.
tcpdump-uw -i vmk1 igmp
On your UCS Fabric Interconnect:
show ip igmp snooping groups
To clean your data you can:
cut -d' ' -f4 (your fabric interconnect output) | sort -u > (new file for fabric interconnect)
cut -d' ' -f5 (your esxi output) | sort -u > (new file for esxi)
Next, run a diff on your two files and anything that exists on esxi but not your FI is your problem! enjoy!