diff --git a/port/include/net/net.h b/port/include/net/net.h
index 6880dd84d..e99179f63 100644
--- a/port/include/net/net.h
+++ b/port/include/net/net.h
@@ -5,7 +5,7 @@
 #include "constants.h"
 #include "net/netbuf.h"
 
-#define NET_PROTOCOL_VER 1
+#define NET_PROTOCOL_VER 2
 
 #define NET_MAX_CLIENTS MAX_PLAYERS
 #define NET_MAX_NAME MAX_PLAYERNAME
@@ -30,6 +30,7 @@
 #define DISCONNECT_TIMEOUT 5
 #define DISCONNECT_FULL 6
 #define DISCONNECT_LATE 7
+#define DISCONNECT_FILES 8
 
 #define CLSTATE_DISCONNECTED 0
 #define CLSTATE_CONNECTING 1
@@ -132,6 +133,7 @@ void netChat(const char *text);
 
 void netServerStageStart(void);
 void netServerStageEnd(void);
+void netServerKick(struct netclient *cl, const u32 reason);
 
 void netPlayersAllocate(void);
 void netSyncIdsAllocate(void);
diff --git a/port/include/romdata.h b/port/include/romdata.h
index d1d411f1e..4f7fdabff 100644
--- a/port/include/romdata.h
+++ b/port/include/romdata.h
@@ -5,6 +5,7 @@
 
 extern u8 *g_RomFile;
 extern u32 g_RomFileSize;
+extern const char *g_RomName;
 
 s32 romdataInit(void);
 
diff --git a/port/src/net/net.c b/port/src/net/net.c
index 65ec8e3a2..446483d86 100644
--- a/port/src/net/net.c
+++ b/port/src/net/net.c
@@ -239,6 +239,25 @@ static inline void netFlushSendBuffers(void)
 	}
 }
 
+static inline const char *netGetDisconnectReason(const u32 reason)
+{
+	static const char *msgs[] = {
+		"Unknown",
+		"Server is shutting down",
+		"Protocol or version mismatch",
+		"Kicked by console",
+		"You are banned on this server",
+		"Connection timed out",
+		"Server is full",
+		"The game is already in progress",
+		"Your files differ from the server's"
+	};
+	if (reason < (u32)ARRAYCOUNT(msgs)) {
+		return msgs[reason];
+	}
+	return msgs[0];
+}
+
 void netInit(void)
 {
 	if (enet_initialize() < 0) {
@@ -319,6 +338,19 @@ void netServerStageEnd(void)
 	netSend(NULL, &g_NetMsgRel, true, NETCHAN_CONTROL);
 }
 
+void netServerKick(struct netclient *cl, const u32 reason)
+{
+	if (g_NetMode != NETMODE_SERVER) {
+		return;
+	}
+
+	if (!cl || !cl->state || !cl->peer) {
+		return;
+	}
+
+	enet_peer_disconnect(cl->peer, reason);
+}
+
 s32 netStartClient(const char *addr)
 {
 	if (g_NetMode || !g_NetInit) {
@@ -405,7 +437,7 @@ s32 netDisconnect(void)
 	g_NetHost = NULL;
 	g_NetMode = NETMODE_NONE;
 
-	sysLogPrintf(LOG_NOTE, "NET: disconnected");
+	sysLogPrintf(LOG_CHAT, "NET: disconnected");
 
 	if (wasingame) {
 		mainEndStage();
@@ -465,7 +497,11 @@ static void netServerEvDisconnect(struct netclient *cl)
 		enet_peer_reset(cl->peer);
 	}
 
-	sysLogPrintf(LOG_CHAT, "NET: %s (client %u) disconnected", cl->settings.name, cl->id);
+	if (cl->settings.name) {
+		sysLogPrintf(LOG_CHAT, "NET: %s (%u) disconnected", cl->settings.name, cl->id);
+	} else {
+		sysLogPrintf(LOG_CHAT, "NET: client %u disconnected", cl->id);
+	}
 
 	netClientReset(cl);
 
@@ -509,10 +545,8 @@ static void netClientEvConnect(const u32 data)
 
 static void netClientEvDisconnect(const u32 reason)
 {
-	sysLogPrintf(LOG_NOTE, "NET: kicked from server, reason: %u", reason);
+	sysLogPrintf(LOG_CHAT, "NET: disconnected from server: %s (%u)", netGetDisconnectReason(reason), reason);
 	netDisconnect();
-
-	sysLogPrintf(LOG_CHAT, "NET: disconnected from server");
 }
 
 static void netClientEvReceive(struct netclient *cl)
diff --git a/port/src/net/netmsg.c b/port/src/net/netmsg.c
index 029b9ac59..028e3f6b4 100644
--- a/port/src/net/netmsg.c
+++ b/port/src/net/netmsg.c
@@ -22,6 +22,8 @@
 #include "game/modelmgr.h"
 #include "game/propsnd.h"
 #include "system.h"
+#include "romdata.h"
+#include "fs.h"
 #include "console.h"
 #include "net/net.h"
 #include "net/netbuf.h"
@@ -141,11 +143,19 @@ static inline s32 propRoomsEqual(const RoomNum *ra, const RoomNum *rb)
 
 u32 netmsgClcAuthWrite(struct netbuf *dst)
 {
+	const char *modDir = fsGetModDir();
+	if (!modDir) {
+		modDir = "";
+	}
+
 	netbufWriteU8(dst, CLC_AUTH);
+	netbufWriteStr(dst, g_RomName); // TODO: use a CRC or something
+	netbufWriteStr(dst, modDir);
 	netbufWriteU8(dst, 1); // TODO: number of local players
 	netbufWriteU8(dst, g_NetLocalClient->settings.bodynum);
 	netbufWriteU8(dst, g_NetLocalClient->settings.headnum);
 	netbufWriteStr(dst, g_NetLocalClient->settings.name);
+
 	return dst->error;
 }
 
@@ -156,15 +166,35 @@ u32 netmsgClcAuthRead(struct netbuf *src, struct netclient *srccl)
 		return 1;
 	}
 
+	const char *romName = netbufReadStr(src);
+	const char *modDir = netbufReadStr(src);
 	const u8 players = netbufReadU8(src);
 	const u8 bodynum = netbufReadU8(src);
 	const u8 headnum = netbufReadU8(src);
 	char *name = netbufReadStr(src);
 	if (src->error) {
 		sysLogPrintf(LOG_WARNING, "NET: malformed CLC_AUTH from %s", netFormatClientAddr(srccl));
+		netServerKick(srccl, DISCONNECT_KICKED);
 		return 1;
 	}
 
+	if (strcasecmp(romName, g_RomName) != 0) {
+		sysLogPrintf(LOG_WARNING, "NET: CLC_AUTH: %s has the wrong ROM, disconnecting", netFormatClientAddr(srccl));
+		netServerKick(srccl, DISCONNECT_FILES);
+		return src->error;
+	}
+
+	if (modDir[0] == '\0') {
+		modDir = NULL;
+	}
+
+	const char *myModDir = fsGetModDir();
+	if ((!myModDir != !modDir) || (myModDir && modDir && strcasecmp(modDir, myModDir) != 0)) {
+		sysLogPrintf(LOG_WARNING, "NET: CLC_AUTH: %s has the wrong mod, disconnecting", netFormatClientAddr(srccl));
+		netServerKick(srccl, DISCONNECT_FILES);
+		return src->error;
+	}
+
 	strncpy(srccl->settings.name, name, sizeof(srccl->settings.name) - 1);
 	srccl->settings.bodynum = bodynum;
 	srccl->settings.headnum = headnum;
@@ -176,7 +206,7 @@ u32 netmsgClcAuthRead(struct netbuf *src, struct netclient *srccl)
 	netmsgSvcAuthWrite(&srccl->out, srccl);
 	netSend(srccl, NULL, true, NETCHAN_CONTROL);
 
-	sysLogPrintf(LOG_CHAT, "NET: %s (client %u) joined", srccl->settings.name, srccl->id);
+	sysLogPrintf(LOG_CHAT, "NET: %s (%u) joined", srccl->settings.name, srccl->id);
 
 	return 0;
 }
diff --git a/port/src/romdata.c b/port/src/romdata.c
index effc67e65..d31db357f 100644
--- a/port/src/romdata.c
+++ b/port/src/romdata.c
@@ -53,10 +53,10 @@
 
 u8 *g_RomFile;
 u32 g_RomFileSize;
+const char *g_RomName = ROMDATA_ROM_NAME;
 
 static u8 *romDataSeg;
 static u32 romDataSegSize;
-static const char *romName = ROMDATA_ROM_NAME;
 
 enum loadsource {
 	SRC_UNLOADED = 0,
@@ -188,12 +188,12 @@ static inline void romdataWrongRomError(const char *fmt, ...)
 
 static inline void romdataLoadRom(void)
 {
-	sysLogPrintf(LOG_NOTE, "ROM file: %s", romName);
+	sysLogPrintf(LOG_NOTE, "ROM file: %s", g_RomName);
 
-	g_RomFile = fsFileLoad(romName, &g_RomFileSize);
+	g_RomFile = fsFileLoad(g_RomName, &g_RomFileSize);
 
 	if (!g_RomFile) {
-		sysFatalError("Could not open ROM file %s.\nEnsure that it is in the %s directory.", romName, fsFullPath(""));
+		sysFatalError("Could not open ROM file %s.\nEnsure that it is in the %s directory.", g_RomName, fsFullPath(""));
 	}
 
 	// zips are not guaranteed to start with PK, but might as well at least try
@@ -368,7 +368,7 @@ s32 romdataInit(void)
 {
 	const char *altRomName = sysArgGetString("--rom-file");
 	if (altRomName) {
-		romName = altRomName;
+		g_RomName = altRomName;
 	}
 
 	romdataLoadRom();