I switched to an ISP with native IPv6 support and am trying to setup Asterisk with IPv6 as well. While my current configuration seems to work with IPv4 I get some weird errors when testing IPv6.
While searching for a solution I found out that pjproject doesn't get build with IPv6 support by default:
pjlib supports IPv6, but for now this has to be enabled in pj/config_site.h:
#define PJ_HAS_IPV6 1
The Asterisk wiki mentions this as well: https://wiki.asterisk.org/wiki/display/AST/PJSIP-pjproject