vrrp multicast bind to interface, ipv4 vs ipv6

Hi,

With regards to vrrp and the sending of multicast packets, keepalived 
achieves this by setting the options of the send sockets to BINDTODEVICE 
for ipv4 and MULTICAST_IF to ipv6. Is there any specific reason why ipv4 
uses BINDTODEVICE, but ipv6 uses MULTICAST_IF? What's the difference here?

Thanks,
David

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