I recently added IPv6 to the ONMS.Net server and wanted to configure Varnish to cache pages on both specific IPv4 and IPv6 addresses. Searching the topic didn't return any clear cut answers, so here goes for all of you that need a specific answer:
varnishd -a IPv4:80,[IPv4]:80 -b [IPv4 or IPv6]:8080 -s malloc,128M
The Varnish listen on option or -a can be given multiple addresses, so we add IPv4 and IPv6 addresses using: -a IPv4:Port,[IPv6]:Port
The backend server option or -b can be either an IPv4 or IPv6, in my case I take IPv4 and IPv6 requests and send them to the web server listening on IPv6 since were moving to IPv6 in any case.
The above command should run however you may want to tweak the other Varnish parameters for your specific setup...
Hope this helps someone!