Grandstream GXV3240 Administration Guide - Manual (Page 51)

Firmware Version 1.0.3.37 GXV3240 Administration Guide Page 49 of 117
ACCOUNT/NETWORK SETTINGS
Outbound Proxy
It is used to configure the IP address or the Domain name of the
Primary Outbound Proxy, Media Gateway, or Session Border
Controller. It's used by the phone for Firewall or NAT penetration in
different network environments. If a symmetric NAT is detected, STUN
will not work and ONLY an Outbound Proxy can provide a solution.
Secondary Outbound Proxy
It is used to configure the IP address or the Domain name of the
Secondary Outbound Proxy, Media Gateway, or Session Border
Controller. The phone system will try to connect the Secondary
outbound proxy only if the primary outbound proxy fails.
DNS Mode
It is used to set which DNS service will be used to lookup IP address
for SIP server’s hostname. It can be selected from the dropdown list:

A Record

SRV

NATPTR/SRV.
If it needs DNS SRV resource, which DNS server response more than
one result, it should be set to "SRV" or "NATPTR/SRV". The default
setting is "A Record".
NAT Traversal
It is used to configure which NAT traversal mechanism will be enabled
on the phone system. It can be selected from the dropdown list:

NAT NO

STUN

Keep-alive

uPnP

Auto

VPN
If the outbound proxy is configured and used, it can be set to “NAT
NO”.
If set to "STUN" and STUN server is configured, the phone system will
periodically send STUN message to the SUTN server to get the public
IP address of its NAT environment and keep the NAT port open. STUN
will not work if the NAT is symmetric type.
If set to “Keep-alive”, the phone system will send the STUN packets to
maintain the connection that is first established during registration of
the phone. The “Keep-alive” packets will fool the NAT device into
keeping the connection open and this allows the host server to send
SIP requests directly to the registered phone.
If it needs to use OpenVPN to connect host server, it needs to set it to
“VPN”.