Draytek Vigor2500V Manual page 58

NAT
After the public IP addresses are kept within NAT IP pool, these public IP
addresses are selectable on NAT/Open Ports menu. For example, you can
specify one computer for XBox Live by open UDP port and TCP port:
The Vigor2500V series shall be compatible with XBox Live. If it does not work in
the default configuration, you can open UDP Ports 88 and 3074 and TCP Port
3074 to redirect the Xbox's local IP address.
You select one public IP (e.g. 61.230.203.39) to the specified computer on the
LAN. The specified computer is with private IP address 192.168.1.20. XBox Live
will not be prevented from Vigor router after you open UDP Ports 88 and 3074,
and TCP Port 3074.
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