Dark MultiPlayer Connection Errors Fixed (KSP DMP)

Q: My friend reinstalled KSP and now gets Invalid key for user. Will they lose their ships?

No. Delete their file in Universe/Players on the server. Vessels are stored separately and stay.

Most Dark MultiPlayer connection failures fall into five messages. Failed to connect - no reply or Initial connection timeout means the client cannot reach TCP port 6702. Protocol mismatch means the client and server are on different DMP versions. Invalid key for user means that player name was registered by a different install. Failed mod validation means the player's GameData does not match the server's mod list. You are not on the whitelist means exactly that. The status line in the DarkMultiPlayer window tells you which one you have.

A Kerbal Space Program spacecraft in orbit

Read the status line first

The DarkMultiPlayer window on KSP's main menu shows each step of a connection: Connecting, Handshaking, Syncing modpack, Syncing server clock, Syncing universe time, Starting game, Running. Where it stops tells you where to look:

Stops at	Area
`Connecting to ... port 6702` then a timeout	Network: port, firewall, address
`Handshaking` then a disconnect message	Version, player name key, ban, whitelist, server full
After handshake with mod messages	Mod control
Later, during sync	Usually a corrupted vessel or a heavy universe, check the server log

The server console logs every connection attempt too. Have it open while a friend tries.

"Failed to connect - no reply" and "Initial connection timeout"

The client never got an answer. In order of likelihood:

Wrong port or protocol forwarded. DMP uses TCP, not UDP. Forward TCP 6702 (or the port from Config/Settings.txt).
Firewall. Allow DMPServer.exe (or Mono on Linux) through the OS firewall.
Wrong address. Players outside your network use your public IP. Players on the same network use the LAN IP, because many routers do not loop back to their own public address.
CGNAT. If your router's WAN IP differs from what a "what is my IP" site shows, port forwarding cannot work at all. See hosting without port forwarding.
Server not ready. Wait for Ready! in the server console before connecting.

"DNS does not contain a valid address entry" or "Address is not a IP or DNS name"

The address field has a typo or extra characters. Enter a plain IP or hostname in the address box and the number in the port box, not host:port in one field.

"Error setting up server ... This protocol version is not supported"

That is a server side error on machines without IPv6. Set supportIpv6 to False in Config/Settings.txt and restart.

"Protocol mismatch"

The client and server speak different versions of the DMP protocol. Everyone, server included, must be on the same DMP release.

Check the version in the title of the DarkMultiPlayer window, for example DarkMultiPlayer v0.3.8.5.
Download the matching DMP Client from d-mp.org. Old versions are listed under each download button if your server is behind.
Delete the old GameData/DarkMultiPlayer folder before copying the new one, so old files do not linger.

Disconnected from pre-v0.2 DMP server and Disconnected from non-DMP server mean you have reached something that is not a current DMP server: an ancient install, or the wrong port entirely.

"Invalid key for user" and "Public/private key mismatch"

DMP ties each player name to a key the first time it connects, stored on the server in Universe/Players/<name>.txt. If that player reinstalls KSP, moves to a new PC, or a second person tries the same name, the key no longer matches and the server refuses them.

Fix it on the server:

Stop the server.
Delete Universe/Players/<name>.txt for the affected name.
Start the server and connect. The new key is registered.

The player's vessels stay, since they are stored in Universe/Vessels/. Only the name lock is reset. Do this only for someone you are sure is the real owner of the name.

"Kicked for using a reserved name"

The names Initial, Shared and whatever consoleIdentifier is set to (default Server) are reserved. Pick another name.

"Failed mod validation"

A Kerbal Space Program vessel above Kerbin

The server's mod-control.txt lists files that must be present, must not be present, or must match a hash. The disconnect message lists what is wrong, for example:

Required file MechJeb2/Plugins/MechJeb2.dll is missing!
Required file ... does not match hash ...
Banned resource ... exists on client!
Required part ... is missing!

Either install exactly the listed mods at the same versions, or have the server owner regenerate the list from a clean install. The full process is in our guide on using mods on a DMP server.

"You are not on the whitelist"

The server has whitelisted set to true and the name is not listed. An admin runs this in the server console:

/whitelist add PlayerName
/whitelist show

The name is the DMP player name, which is case sensitive in practice. Copy it exactly.

Other handshake messages

Message	Meaning	Fix
`Server is full`	`maxPlayers` reached	Raise it in `Settings.txt`
`You were banned from the server!`	Name, IP or key is banned	Check `Config/banned-players.txt`, `banned-ips.txt` and `banned-keys.txt`
`Client already connected`	Same name still connected, often after a crash	Wait for the old session to time out, or `/kick` it
`Invalid username`	Empty or illegal characters	Use a plain name

Connected, but vessels are missing or the game stalls

Missing parts: someone launched with a parts mod you do not have. Mod control prevents this when it is set up.
Long sync on join: a universe full of debris. Run /dekessler in the server console, and keep autoDekessler on.
Pad blocked at KSC: run /nukeksc to clear every vessel at KSC and the runway.

Skip the network part

Most DMP connection problems are home network problems. A KSP DMP server from GamezServers has its own address and assigned port, so friends paste it into Add Server with no router to configure. You still need matching client versions, but whitelist, admin and debris commands run from the live console in the panel, and deleting a stale key file in Universe/Players takes seconds in the file manager. For setting a server up from scratch, see our DMP hosting guide.

FAQ

Does DMP use TCP or UDP?

TCP. The default port is 6702. Forward TCP, not UDP.

Why can I connect locally but my friend cannot?

You are using the LAN address, they need your public IP, and that path is blocked by port forwarding, a firewall or CGNAT.

My friend reinstalled KSP and now gets Invalid key for user. Will they lose their ships?

No. Delete their file in Universe/Players on the server. Vessels are stored separately and stay.

Can I join a DMP server from KSP 2?

No. DMP only works with Kerbal Space Program 1.12.