Vanilla Doom

From ZDoom Wiki

Vanilla Doom is used to refer to Doom running without a source port on the original executable. In order to avoid desynchronizations in multiplayer, players must have their vanilla Doom's IWAD patched to 1.9. Rebuilding the NODES in the original maps will also cause them to desynchronize. Foreign language versions of the vanilla Doom IWADs may have rebuilt versions of the nodes as well, making them incompatable with one another in multiplayer.