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# Multiplayer

DOS multiplayer games used two main networking approaches: serial connections (modem dial-up or direct null modem cable) for head-to-head play, and IPX for LAN parties. DOSBox Staging emulates both over modern internet connections.

Tip

For per-game setup instructions and troubleshooting, see the Multiplayer & Serial Ports wiki page.

## Serial multiplayer

Games like Doom, Rise of the Triad, and Terminal Velocity supported modem or null modem play. DOSBox Staging’s serial port emulation handles both.

### Modem mode

Modem mode emulates a Hayes-compatible dial-up modem. One player listens for incoming calls; the other dials their IP address (or hostname) using the game’s built-in dial-up interface — the same `ATDT` commands real modems used, just routed over the internet instead of a phone line.

The host listens on a port:

    [serial]
    serial1 = modem listenport:5000 sock:1

The client dials the host’s address from within the game, e.g., `ATDT 203.0.113.5:5000`.

Some games have restrictive phone number input fields that won’t accept IP addresses. You can work around this with a phonebook file — map fake phone numbers to real addresses in `phonebook.txt` (or whatever filename you’ve set via `phonebookfile`):

    5551234 203.0.113.5:5000

Now dialling `5551234` in the game connects to your friend’s machine.

### Nullmodem mode

Nullmodem mode creates a direct serial link between two DOSBox instances, skipping the modem handshake entirely. This is the simplest option when both players can coordinate outside the game.

The host listens on a port:

    [serial]
    serial1 = nullmodem port:1250 sock:1

The client connects to the host:

    [serial]
    serial1 = nullmodem server:203.0.113.5 port:1250 sock:1

The connection is established as soon as both sides start DOSBox — no dialling required. The game sees a standard serial connection on COM1.

### ENet reliable UDP transport

By default, both modem and nullmodem modes use TCP. Adding `sock:1` switches to ENet, a reliable UDP-based transport. For internet play, ENet is strongly preferred — it has lower latency than TCP and is more resilient on unreliable connections. Both sides must use the same transport.

## IPX multiplayer

LAN-party games like Duke Nukem 3D, WarCraft II, and Command & Conquer used the IPX protocol. DOSBox Staging tunnels IPX over modern UDP/IP. One player starts a server, others connect to it:

    IPXNET STARTSERVER
    IPXNET CONNECT 203.0.113.5

See the IPX page for configuration details.

## Port forwarding and firewalls

In both serial and IPX multiplayer, the host needs the chosen port to be reachable from the internet. If the host is behind a router or NAT, this typically means setting up port forwarding for that single port (UDP when using `sock:1` or IPX, TCP otherwise).

If neither player can forward a port, a VPN such as ZeroTier or Tailscale is the easiest alternative — both players join the same virtual network and connect using their VPN-assigned addresses, with no port forwarding needed.