LAN discovery broken on BDS for Ubuntu (Linux) 1.26.20+ when`online-mode=true`

Environment

• Server software: Minecraft Bedrock Dedicated Server (BDS) for Linux (Ubuntu 24.04)

• Server versions affected: 1.26.20.4, 1.26.20.5, 1.26.21.1

• Last known working version: 1.26.14.1

• Client platforms tested: Windows 11 Bedrock, PlayStation 5

• Network: Local LAN, same subnet, IPv4 only

• server.properties: online-mode=true (default)

• Firewall: UDP port 19132 allowed (verified on server)

Steps to reproduce

1. Start Bedrock Dedicated Server on Ubuntu with default configuration (online-mode=true).

2. Ensure client device (Windows 11 or PS5) is on the same LAN.

3. Open Minecraft client and go to Worlds tab (LAN/server discovery list).

4. Attempt to join the discovered server entry.

Expected result

Client is able to connect successfully (as in version 1.26.14.1 and earlier).

Actual result

Server appears in LAN list, but connection fails immediately with:

Unable to connect to world.
Search help.Minecraft.net for "Boat" for more information.

ERROR DETAILS
Win,D,,GC-10.0.26200.8457 Error Detail InitialConnection-108:
Version: 1.26.21-Windows GDK Build
Transport: RakNet:975
NetworkType: 1

The problem does not occur when either:

• the client is connected via the Creator Multiplayer tab using the server’s direct IP address and port (Windows only),

• online-mode=false is set on the server (which is not an acceptable solution because online authentication is mandatory).

Network observations (supplementary)

I compared UDP packet captures of a failed LAN discovery with a capture from a working scenario.

The client’s Unconnected Ping is structurally identical in both cases – no difference that could explain the error.

The only divergence is in the server’s Unconnected Pong payload. The semicolon-separated info string ends with:

• Failing (online-mode=true): ...19132;19133;0;0;0;

• Working (online-mode=false / earlier version): ...19132;19133;0;1;0;

The 14th field (0-indexed 13) changes from 1 to 0.
A tentative interpretation is that this flag may signal to the client whether a connection is permitted, and the newer server sets it to 0 when online-mode=true, leading the client to abort the connection immediately with the “Boat” / InitialConnection-108 error. The exact purpose of this flag is not officially documented; this is an observation, not a confirmed root cause.

Workaround (Windows only)

Add the server manually in the Creator Multiplayer tab using its local IP and port (e.g., 192.168.x.x:19132). This bypasses LAN discovery and works correctly.

Notes

• The issue also occurs with a fresh server installation using all default settings (including online-mode=true).

• The regression was introduced between server versions 1.26.14.1 and 1.26.20.4.

• I have not tested the Windows version of the dedicated server; this report covers only the Ubuntu Linux build.

• The server is otherwise fully functional; the issue is limited to the broadcast-based LAN discovery mechanism.