Unable to start local multiplayer without internet connection

[Benedikt Straub]

When no internet connection is present, trying to start a LAN multiplayer game is not possible because "Network is unreachable". An error message is shown and Widelands goes back to the main menu.
Playing on localhost only (e.g. AI-only games, loading a MP savegame) should be possible even if there is no network connection.

[Toni Förster (stonerl)]

When exactly does this happen? After clicking "LAN/ Direct IP","host game", "joing game" or "start game"?

[Benedikt Straub (nordfriese)]

Immediately after clicking LAN/directIP in the main menu.

[LAN] Trying to open both sockets.
[LAN] Started an IPv4 socket on UDP port 7394.
[LAN] Started an IPv6 socket on UDP port 7394.
[LAN] Will broadcast for IPv6.
[LAN] Error when broadcasting on IPv6 socket to ff02::1, closing it: Network is unreachable.
[LAN] Closing an IPv6 socket.
[LAN] Closing an IPv4 socket.

Warning: Kunn de stedenwies Nett nich bruken!
Widelands kunn de stedenwies Nett nich bruken. Wahrschienelk bedrifft een annerer Prozess al eenen Server up Port 7394, 7395 oder 7396 oder diene Nett-Instellungen sünd kaputt.

[Toni Förster (stonerl)]

I'd say "diene Nett-Instellungen sünd kaputt" :)

If you're not connected to a network you should at least see this:

[LAN] Will broadcast to 127.0.0.1.

At least that is what happens on my machine. I wonder why it does not broadcast on IPv4 on your system? Have you disabled v4 on your system? What is the output when you're connected to a network?

[Benedikt Straub (nordfriese)]

I´m using IPv4 as far as I know. At least my IP address has four numbers in it…
Output when I´m connected to the internet:

[LAN] Started an IPv4 socket on UDP port 7394.
[LAN] Started an IPv6 socket on UDP port 7394.
[LAN] Will broadcast to 192.168.2.255.
[LAN] Will broadcast for IPv6.
[Host]: starting up.
[NetHost]: Opening a listening IPv4 socket on TCP port 7396
[NetHost]: Opening a listening IPv6 socket on TCP port 7396
[LAN] Started an IPv4 socket on UDP port 7395.
[LAN] Started an IPv6 socket on UDP port 7395.
[LAN] Will broadcast to 192.168.2.255.
[LAN] Will broadcast for IPv6.
Initializing economy serial
lastserial: 0

Instructions how to reproduce on Ubuntu 19.04:
– Disable WLAN (if present) and use a LAN cable. Check that you can open websites etc.
– Start Widelands. Multiplayer works correctly.
– Return to the main menu
– Pull out the LAN cable
– Try to start a MP game, and you get the output in #2
– Re-insert the LAN cable and check that you can open websites etc
– Multiplayer works correctly again

[Toni Förster (stonerl)]

Well technically speaking, you're connected to your local network that happens to be connected to the internet. I think this is a configuration problem. What happens if you disconnect your router from the internet but still have your computer connected to your router?

I assume you still broadcast to 192.168.2.255.

When you remove the Ethernet-Cable, are you still able to ping localhost?

[GunChleoc (gunchleoc)]

When I disable my WLAN connection, an already running local AI multiplayer game will still continue, but I can't enter the LAN lobby.

[Toni Förster (stonerl)]

Cannot reproduce this on my mac. What OS are you using? Windows or Linux?

[GunChleoc (gunchleoc)]

I'm on Linux Mint

[Toni Förster (stonerl)]

Okay, I tested this on Windows 10 and there it also doesn't happen.

So this is either a Linux problem. Or a problem of Ubuntu based distributions.

@kaputtnik can you test this with your Arch machine?

[Toni Förster (stonerl)]

I think I know what's going on. 127.0.0.1 is assigned to the loopback device lo. But it seems that widelands tries to use the LAN or Wi-Fi interface and ignores the loopback device on linux.

[kaputtnik (franku)]

On archlinux it's the same like it is on Ubuntu:

[LAN] Trying to open both sockets.
[LAN] Started an IPv4 socket on UDP port 7394.
[LAN] Started an IPv6 socket on UDP port 7394.
[LAN] Will broadcast for IPv6.
[LAN] Error when broadcasting on IPv6 socket to ff02::1, closing it: Network is unreachable

Isn't it normal that Lan games won't work (in the intentional meaning of playing with other people in a network) if there is no network connection established?

[GunChleoc (gunchleoc)]

I think it's OK like this for normal gameplay, but would be nice to have for local testing using multiplayer games.

[GunChleoc (gunchleoc)]

Migrated to https://github.com/widelands/widelands/issues/593