Reference Manual


sethtx - Interact with the Host Transfer Mode mechanism


sethtx [ifn | all [on | off | block | allow]]



Tip To view available interfaces, click here: NAT32 Interface Popup
Tip To view the Windows Routing Table, click here: Windows Routing Table Popup


In Host Transfer Mode, all Windows Internet traffic for the specified interface ifn is sent and received via NAT32.

When Host Transfer Mode is off, Windows sends and receives all Internet traffic via its current default route and does not interact with NAT32 in any way.

When Host Transfer Mode is on, the MSTCP stack bound to the specified interface is completely isolated and no IPv4 packets of any type can be sent or received. Even the OS itself cannot remove the block, and the only way that applications can communicate with other computers is via NAT32. This greatly enhances security and allows networking applications to aggregate traffic over multiple Internet connections.

It is strongly recommended that you run NAT32 in Host Transfer Mode at all times so that all unsolicited traffic from the Internet is blocked from the Windows TCP/IP stack.

Note that this recommendation applies even in the presence of software firewalls, because malicious applications and the OS itself can manipulate such firewalls at will.

Argument ifn should always be a NAT32 interface number that matches the interface of a Windows default route.

If argument ifn is specified as all, then the Host Transfer Mode is turned on for all Internet interfaces and all Internet traffic then passes through the NAT32.

If existing connections are to remain undisturbed, turn on Host Transfer Mode only after the needed winmap tcp and winmap udp commands have been issued.

No version of Windows to date handles multiple Internet connections in a sensible manner. At best, Windows will monitor traffic from the current default gateway and switch to another gateway if the original gateway is not responding. Traffic aggregation over multiple gateways has never been supported.

NAT32's Host Transfer Mode works by intercepting Windows IPv4 traffic and forwarding it via an interface chosen by an Interface Selection Algorithm. The desired selection algorithm is specified with the setis command.

The Host Transfer Mode should not be enabled if Windows IP Forwarding is on. This is because UDP packet cycles can occur in this case. The winrt command can be used to turn off Windows IP Forwarding.

For Dial-Up Networking connections, Host Transfer Mode can be turned on by adding the following command to the end of the connect.txt script file:

sethtx $2 on

Similarly, when the connection is closed, adding the following command to the end of the disconnect.txt file will turn off Host Transfer Mode:

sethtx $2 off

For all other Internet connections, Host Transfer Mode can be turned on in file user.txt and off in file exit.txt.

setis, winrt