Linksys ATA Administration Guide
173
Q.
My ATA device is behind a NAT device or firewall and I’m unable to make a call or I’m only
receiving a one-way connection. What should I do?
A:
1. Configure your router to port forward “TCP port 80" to the IP address currently being used
by your Linksys ATA device. If you do this often, we suggest that you use static IP address for
the ATA device, instead of DHCP. (For help with port forwarding, consult your router
documentation)
2. On the Line tab of the administration web server, change the value of
Nat Mapping Enable
to
yes
. On the SIP tab; change
Substitute VIA Addr
to
yes
, and the
EXT IP
parameter to the IP
address of your router.
3. Make sure you are not blocking the UDP PORT 5060,5061 and port for UDP packets in the
range of 16384-16482. Also, disable “SPI” if this feature is provided by your firewall. Identify
the SIP server to which the ATA device is registering, if it supports NAT, using the
Outbound
Proxy
parameter.
4. Add a STUN server to allow traversal of UDP packets through the NAT device. On the SIP tab
of the administration web server, set
STUN Enable
to
yes
, and enter the IP address of the
STUN server in
STUN Server
.
STUN (Simple Traversal of UDP through NATs) is a protocol defined by RFC 3489, that allows
a client behind a NAT device to find out its public address, the type of NAT it is behind, and
the port associated on the Internet connection with a particular local port. This information
is used to set up UDP communication between two hosts that are both behind NAT routers.
Open source STUN software can be obtained at the following website:
http://www.voip-info.org/wiki-Open+VOIP+Software
NOTE:
STUN does not work with a symmetric NAT router. Enable debug through syslog (see
FAQ#10), and set
STUN Test Enable
to
yes
. The messages indicate whether you have symmetric
NAT or not.