This object indicates whether the primary destination address for this association is IPv4, IPv6, or unknown, the last used for error conditions or when the corresponding address is a zero-length string. This matters on a dual-stack signaling gateway where some peers are still reached over IPv4 and others have migrated to IPv6; a value of unknown on an association that should be active is itself a red flag that the primary path was never properly negotiated. Seeing ipv4 on an association that was expected to use a newly configured IPv6 peer address would indicate the IPv6 path negotiation did not take effect.