Lync Server 2013 has added support for IPv6 addressing of all server roles, which can operate in a mixed IPv4 and IPv6 mode as organizations begin migrating internal networks to IPv6.
There is no support for down-level clients like Office Communicator 2007 R2 or Lync 2010 in a dual-stack site, so companies need to first migrate users to Lync Server 2013 in order to implement IPv6 support.
Some of the advanced voice features such as Call Admission Control, E911, and Media Bypass do not fully support IPv6. The Lync Phone Edition software also does not support IPv6. Organizations requiring these features should plan on supporting a dual-stack approach for this release.