IPv6: IS-IS or OSPFv3

For IS-IS, highly recommend MT to avoid any nasties while
turning up v6 in a dual-stack environment.

Also when doing MT on cisco, configure "no-adjacency-check" under the v6 address-family during the migrate
else you will bounce your sessions.

Cisco of course warn you against doing this but without it the change is bumpy.

From the cisco docs:

"Disabling the adjacency-check command can adversely affect your network configuration. Enter the no adjacency-check command only when you are running IPv4 IS-IS on all your routers and you want to add IPv6 IS-IS to your network but you need to maintain all your adjacencies during the transition. When the IPv6 IS-IS configuration is complete, remove the no adjacency-check command from the configuration."

source: http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-is-is.html