How do we define broadcast domains in Dualstack mode(IPV4 & IPV6)? I have a layer3 edge device having a vlan with both ipv4 and ipv6 subnet.is broadcast domain changes from ipv4 to ipv6 if these are in same vlan?
There is no broadcast in IPv6 - all one-to-many communications are handled via link-local multicast groups.
That said, if your switch(es) are not configured to snoop this traffic, it will be flooded across all interfaces in the same VLAN regardless.
To answer your question though - these domains are both identical - they both exist amongst all ports within a VLAN. The only difference would be that if you have your switch configured to snoop, your IPv6 domain will be limited to IPv6 speaking hosts, where as IPv4 broadcasts will be sent to all hosts - even IPv6-only speakers.