Nat And Sip; Sip Alg; Use Nat; Stun - ZyXEL Communications P-2302R-P1 Series User Manual

9.1.7 NAT and SIP

The ZyXEL Device must register its public IP address with a SIP register server. If there is a
NAT router between the ZyXEL Device and the SIP register server, the ZyXEL Device
probably has a private IP address. The ZyXEL Device lists its IP address in the SIP message
that it sends to the SIP register server. NAT does not translate this IP address in the SIP
message. The SIP register server gets the ZyXEL Device's IP address from inside the SIP
message and maps it to your SIP identity. If the ZyXEL Device has a private IP address listed
in the SIP message, the SIP server cannot map it to your SIP identity. See
107 for more information about NAT.
Use a SIP ALG (Application Layer Gateway), Use NAT, STUN, or outbound proxy to allow
the ZyXEL Device to list its public IP address in the SIP messages.

9.1.7.1 SIP ALG

See Section 8.1.3 on page

9.1.7.2 Use NAT

If you know the NAT router's public IP address and SIP port number, you can use the Use
NAT feature to manually configure the ZyXEL Device to use a them in the SIP messages. This
eliminates the need for STUN or a SIP ALG.
You must also configure the NAT router to forward traffic with this port number to the
ZyXEL Device.

9.1.7.3 STUN

STUN (Simple Traversal of User Datagram Protocol (UDP) through Network Address
Translators) allows the ZyXEL Device to find the presence and types of NAT routers and/or
firewalls between it and the public Internet. STUN also allows the ZyXEL Device to find the
public IP address that NAT assigned, so the ZyXEL Device can embed it in the SIP data
stream. STUN does not work with symmetric NAT routers or firewalls. See RFC 3489 for
details on STUN.
The following figure shows how STUN works.
1 The ZyXEL Device (A) sends SIP packets to the STUN server (B).
2 The STUN server (B) finds the public IP address and port number that the NAT router
used on the ZyXEL Device's SIP packets and sends them to the ZyXEL Device.
3 The ZyXEL Device uses the public IP address and port number in the SIP packets that it
sends to the SIP server (C).
Chapter 9 SIP
109.
P-2302R-P1 Series User's Guide
Chapter 8 on page
119