VMAC, vmac_xmit_base, and IGMP

Hi,

"playing" with the VMAC feature on a keepalived 1.2.13 driven cluster of 
balancers, I noticed a peculiar "feature" that I saw no mention of in the 
documentation. Thought I'd note it here...

I am running a ping to the VRRP address from an internal host. Then I restart 
one of the BACKUP keepaliveds. And notice a single ping to receive an "ICMP 
host unreachable" reply with source the IP address of that BACKUP balancer.

Looking into it with tcpdump, I notice that when the daemon starts, it sends 
IGMP messages with source MAC the VMAC - thus teaching the switch, for a short 
while, that it would like to have packets for the VMAC.

Adding vmac_xmit_base to the configuration fixes the issue - the IGMP messages 
are then sent with the base interface source MAC address.

In practise the "error interval" will probably be smaller, due to the MASTER 
balancer more continuously sending packets with VMAC source - my test setup 
has no operational traffic or I probably wouldn't have noticed.

I don't know whether this could be considered a bug, or at what priority, or 
what to do about it, except maybe adding another reason in the docs why 
vmac_xmit_base might be a good idea.

I'll close with a curious question: are there reasons why vmac_xmit_base is 
NOT a good idea?

best regards
  Patrick 

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