IPv6 and NAT64 support 

Availability 

IPv6 support is available in the following platforms:

Windows families, e.g.: Windows 7/8/10, Windows XP, Windows Server 2003, and Windows Vista, using Microsoft Platform SDK for Windows Server 2003 SP1
Linux/Unix/MacOS X with GNU development systems, IPv6 features are detected by the ./configure script.
iOS
Android
Symbian (deprecated)

IPv6 Support in pjlib

The work for adding IPv6 support in pjlib is documented by ticket #415.

pjlib supports IPv6, but for now this has to be enabled in pj/config_site.h:

#define PJ_HAS_IPV6 1

Socket Addresses:

An IPv4 socket address is represented by pj_sockaddr_in structure, while an IPv6 socket address is represented by pj_sockaddr_in6 structure. The pj_sockaddr is a union which may contain IPv4 or IPv6 socket address, depending on the address family field.
Various new socket address API’s have been added which can work on both IPv4 and IPv6 address, such as:

Socket and IOQueue API:

The pj_sockaddr structure is a union which may contain IPv4 or IPv6 socket address. Application may pass this structure to various pjlib socket functions which take pj_sockaddr_t as an argument, such as pj_sock_bind(), pj_sock_sendto(), pj_sock_recvfrom(), pj_sock_accept(), etc.
The pj_ioqueue_t also supports IPv6 sockets.

Address Resolution API:

A new API pj_getaddrinfo() has been added to resolve both IPv4 and IPv6 addresses, in addition to existing pj_gethostbyname() API which resolves IPv4 address.
The pj_gethostip() and pj_getdefaultipinterface() API has been modified to take an additional address family argument.

IP Helper API:

The pj_enum_ip_interface() API has been modified to take an additional address family argument.

IPv6 Support in pjsip

The work for adding IPv6 support in pjlib is documented by ticket #421.

IPv6 SIP Transport:

The SIP UDP transport now supports IPv6 sockets, and new API’s have been added to facilitate IPv6 transport creation (pjsip_udp_transport_start6() and pjsip_udp_transport_attach2()). Note that if application wants to support both IPv4 and IPv6 UDP transports, two separate UDP transport instances must be created, one for each address family.
The SIP TCP and TLS transports also support IPv6 sockets since version 2.1 (ticket #1585).

IPv6 Address Representation:

IPv6 address may appear in two types of places in the SIP message: in a host part of a header field (such as host part of an URI, or host part in a Via header), and as a parameter value (such as the value of received and maddr parameter).
Although in the SIP ABNF grammar an IPv6 may or may not be enclosed in square brackets ([ and ] characters), in pjsip all IPv6 addresses will be represented without the square brackets, for consistency. This means pjsip will remove the square brackets, if they are present, during parsing process, and will enclose the address with square brackets as necessary when pjsip prints the Ipv6 address in a packet for transmission. When application inspects a message component that contains IPv6 address, it will always find it without the enclosing brackets.

IPv6 Support in pjlib-util (DNS SRV and AAAA resolution)

The work for adding IPv6 support in pjlib-util is documented by ticket #419 and continued in ticket #1927.

DNS AAAA resolution will be performed for each DNS SRV record when flag PJ_DNS_SRV_RESOLVE_AAAA or PJ_DNS_SRV_RESOLVE_AAAA_ONLY is set in option param when invoking pj_dns_srv_resolve(). Also flag PJ_DNS_SRV_FALLBACK_AAAA will allow resolver to fallback to DNS AAAA resolution when the SRV resolution fails.

IPv6 Support in pjmedia (SDP, media transport)

The work for adding IPv6 support in pjmedia is documented by ticket #420.

The SDP representation has been updated to support IPv6 address, and the UDP media transport now also supports IPv6 sockets. There have been some incompatible changes introduced in pjmedia:

the pjmedia_sock_info::rtp_addr_name and pjmedia_sock_info::rtcp_addr_name fields (which describes the media transport address information) has been changed to use pj_sockaddr union rather than pj_sockaddr_in structure which is specific to IPv4,
the pjmedia_stream_info::rem_addr and pjmedia_stream_info::rem_rtcp fields also have been changed to use pj_sockaddr union.

IPv6 Support in pjnath (ICE)

The work for adding IPv6 support in pjnath is documented by ticket #422.

STUN and TURN transports support IPv6 already, and now ICE stream transport support IPv6 too. Also, ICE stream transport has been updated to be able to have multiple STUN and TURN transports and each STUN/TURN transport may use either IPv4 and IPv6.

Modifications in pj_ice_strans_cfg:

Deprecated af field, if it is set, the value will be ignored, address family setting is now specified via STUN/TURN transport setting, i.e: stun_tp.af and turn_tp.af.
Deprecated stun and turn fields, but for backward compatibility, those fields will still be used only if stun_tp_cnt and/or turn_tp_cnt is set to zero.
Added stun_tp and turn_tp as replacement of stun and turn respectively, and they are array so application can have multiple STUN/TURN transports.
Added function pj_ice_strans_stun_cfg_default() and pj_ice_strans_stun_cfg_default() to initialize stun_tp and turn_tp respectively with default values.
Added compile-time settings PJ_ICE_MAX_STUN and PJ_ICE_MAX_TURN to specify maximum number of STUN/TURN transports in each ICE component.

Enabling IPv6 support in application using PJSUA-LIB 

Application needs to configure SIP transport and SIP account with IPv6 support.

Creating SIP transport

Here is sample code for IPv6 SIP transport initializations.

pjsua_transport_config tp_cfg;
pjsip_transport_type_e tp_type;
pjsua_transport_id tp_id = -1;

pjsua_transport_config_default(&tp_cfg);
tp_cfg.port = 5060;

/* TCP */
tp_type = PJSIP_TRANSPORT_TCP6;
status = pjsua_transport_create(tp_type, &tp_cfg, &tp_id);
if (status != PJ_SUCCESS)
    ...

/* UDP */
tp_type = PJSIP_TRANSPORT_UDP6;
status = pjsua_transport_create(tp_type, &tp_cfg, &tp_id);
if (status != PJ_SUCCESS)
    ...

/* TLS */
tp_type = PJSIP_TRANSPORT_TLS6;
tp_cfg.port = 5061;
tp_cfg.tls_setting.ca_list_file = pj_str("<path to CA file>");
tp_cfg.tls_setting.cert_file = ...;
tp_cfg.tls_setting.privkey_file = ...;
tp_cfg.tls_setting.password = ...
status = pjsua_transport_create(tp_type, &tp_cfg, &tp_id);
if (status != PJ_SUCCESS)
    ...

SIP Account

Starting from PJSIP 2.14, you can configure your account’s settings pjsua_acc_config::ipv6_sip_use and pjsua_acc_config::ipv6_media_use to specify your IP address preference. The options are: PJSUA_IPV6_DISABLED, PJSUA_IPV6_ENABLED_NO_PREFERENCE, PJSUA_IPV6_ENABLED_PREFER_IPV4, PJSUA_IPV6_ENABLED_PREFER_IPV6, PJSUA_IPV6_ENABLED_USE_IPV6_ONLY.

If you are using PJSIP before version 2.14, it is recommended to explicitly bind an IPv6 account to an IPv6 SIP transport, i.e: via pjsua_acc_config::transport_id or pjsua_acc_set_transport(). Also, IPv6 usage must be explicitly set for media transport, i.e: via pjsua_acc_config::ipv6_media_use.

Here is sample code for setting up account using IPv6 SIP server (for PJSIP earlier than 2.14).

#define SIP_USER "user"
#define SIP_SERVER "example.com"
//#define SIP_SERVER_IPv6 "[1234::5678]"
#define SIP_PASSWD "pwd"

pjsua_acc_config acc_cfg; pjsua_acc_config_default(&acc_cfg);

acc_cfg.id = pj_str("sip:" SIP_USER "@" SIP_SERVER);
acc_cfg.reg_uri = pj_str("sip:" SIP_SERVER);
acc_cfg.cred_count = 1;
acc_cfg.cred_info[0].realm = pj_str("*");
acc_cfg.cred_info[0].scheme = pj_str("digest");
acc_cfg.cred_info[0].username = pj_str(SIP_USER);
acc_cfg.cred_info[0].data_type = PJSIP_CRED_DATA_PLAIN_PASSWD;
acc_cfg.cred_info[0].data = pj_str(SIP_PASSWD);

/* Bind the account to IPv6 transport */
acc_cfg.transport_id = udp6_tp_id;
// udp6_tp_id is an UDP IPv6 transport ID, e.g: outputed by
// pjsua_transport_create(PJSIP_TRANSPORT_UDP6, …, &udp6_tp_id)

/* Enable IPv6 in media transport */
acc_cfg.ipv6_media_use = PJSUA_IPV6_ENABLED;

/* Finally */
status = pjsua_acc_add(&acc_cfg, PJ_TRUE, NULL);
if (status != PJ_SUCCESS)
    ...

NAT64 

In its doc, Apple suggests/requires that applications are capable of supporting IPv6 DNS64/NAT64 Networks. A common misconception in the SIP world is that by using NAT64, IPv4 and IPv6 interoperability can be automatically achieved (i.e. SIP registration, calls, and media flow will work seamlessly and smoothly between any two endpoints regardless of their address families (IPv4/IPv6)). As the doc says: This (DNS64/NAT64) is an IPv6-only network that continues to provide access to IPv4 content through translation, so a client behind a NAT64 network can reach an IPv4 endpoint, but not necessarily the other way around.

In more detail, an IPv6-only SIP client behind a NAT64 can communicate with IPv6 (or dual stack) server or clients just fine, but will experience problems with IPv4-only server or clients, because there are IPv6 address literals in the SIP/SDP fields (Via, Contact, SDP), which the IPv4 instance cannot understand.

According to RFC 6157 (IPv6 Transition in the Session Initiation Protocol (SIP)):

Section 3.1:

In order to support both IPv4-only and IPv6-only user agents, it is RECOMMENDED that domains deploy dual-stack outbound proxy servers or, alternatively, deploy both IPv4-only and IPv6-only outbound proxies.
Section 4:

An IPv6 node SHOULD also be able to send and receive media using IPv4 addresses, but if it cannot, it SHOULD support Session Traversal Utilities for NAT (STUN) relay usage [8].
Section 4.2:

When following the ICE procedures, in addition to local addresses, user agents may need to obtain addresses from relays; for example, an IPv6 user agent would obtain an IPv4 address from a relay.
Section 4.2:

Implementations are encouraged to use ICE; however, the normative strength of the text above is left at a SHOULD since in some managed networks (such as a closed enterprise network) it is possible for the administrator to have control over the IP version utilized in all nodes and thus deploy an IPv6-only network, for example. The use of ICE can be avoided for signaling messages that stay within such managed networks.

(our note:⇒ which means when network is not standardized to one IP version, the use of ICE is a “must”).

Therefore, to support IPv6-IPv4 interoperability in NAT64 environment:

Our RECOMMENDATION is that when the client is put with an IPv6-only connectivity, the SIP server must also support IPv6 connectivity. For the media, user needs a “dual stack” TURN (a TURN server which supports IPv6 connectivity and able to provide an IPv4 relay address upon request). Then all the application needs to do is enable ICE and use TURN (support for dual stack TURN is only available in PJSIP 2.6 or later).
If 1) is not possible (no IPv6 server or not desirable to use TURN), we will need to replace all IPv6 occurences with IPv4 in the SIP messages and SDP. This feature is available in release 2.7.
1. You need a STUN server which resides in an IPv4 network. Then set your pjsua_config to try IPv6 resolution of the STUN servers.
2. Create UDP6 transport to get an IPv4-mapped address from the above STUN server.
3. Bind account to a specific IPv6 transport, and enable IPv6 in media transport.
4. Set account’s NAT64 option to PJSUA_NAT64_ENABLED.
```
cfg->stun_try_ipv6 = PJ_TRUE;

tp_type = PJSIP_TRANSPORT_UDP6;
status = pjsua_transport_create(tp_type, &tp_cfg, &udp6_tp_id);

// For PJSIP 2.14 and above
acc_cfg.ipv6_sip_use = PJSUA_IPV6_ENABLED_USE_IPV6_ONLY;
acc_cfg.ipv6_media_use = PJSUA_IPV6_ENABLED_USE_IPV6_ONLY;

// For PJSIP earlier than 2.14
// acc_cfg.transport_id = udp6_tp_id; // or tcp6_tp_id or tls6_tp_id
// acc_cfg.ipv6_media_use = PJSUA_IPV6_ENABLED;

acc_cfg.nat64_opt = PJSUA_NAT64_ENABLED;
```

References 

Enable IPv6 in ICE transport/TURN in PJSUA: #1971
NAT64 support for IPv4 interoperability: #2032
IPv6 support in PJNATH: #422
Address resolution: #1926
DNS SRV resolution: #1927

IPv6 and NAT64 support

Availability