mod_skinny currently does not support IPv6 (as of 2014-06-17) According to Cisco documentation, the underlying protocol does support IPv6 for the "G" series phones. (Basically a subset of the models running the java based image.) http://www.cisco.com/c/en/us/support/docs/voice-unified-communications/unified-communications-manager-version-70/112997-cucmipv6-00.html 7906G, 7911G, 7931G, 7942G, 7945G, 7962G, 7965G, and the 7975G It is possible that others would be supported, and are just not listed in the Cisco documentation due to them being past end-of-life. Additional changes will be required to mod_skinny to actually support IPv6, at a bare minimum, the current code has at least one data structure for the server response that contains a fixed layout structure with uint32_t's for IP addresses. If someone has an existing CCM deployment that is using IPv6, sample network captures would be appreciated.