IPv6 for VoIP: dual-stack signalling and media

IPv6 changes address selection, routing, firewall policy, and the role of NAT. A dual-stack phone may prefer IPv6 for SIP while media or a carrier still works only over IPv4.

Test deliberately

• Check A and AAAA records and client preference.
• Verify SIP transport and certificate names over IPv6.
• Inspect SDP for IPv6 media addresses and reachable ports.
• Apply explicit IPv6 firewall rules; do not assume IPv4 rules carry over.
• Test registration, inbound calls, outbound calls, DTMF, transfers, and failover.
• Confirm monitoring sees both address families.

Do not call a system IPv6-ready because one ping succeeds. Validate the complete signalling and media path.

Related: IP cheat sheet, DNS, and RTP ranges.