Grandstream Networks GXV3275 Administration Manual page 44

Secondary Outbound
Proxy
DNS Mode
NAT Traversal
Proxy-Require
STUN will not work and only an outbound proxy can provide a solution
Sets IP address or 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.
Defines 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".
Specifies 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". If the
firewall and the SIP device behind the firewall are both able to use UPNP, it can be
set to "UPNP". The both parties will negotiate to use which port to allow SIP through.
The default setting is "Keep-alive".
Adds the Proxy-Required header in the SIP message. It is used to indicate proxy-
sensitive features that must be supported by the proxy. Do not configure this
parameter unless this feature is supported on the SIP server.
GXV3275 Administration Guide
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