Merge PR #828: Added the "OpenVPNPushDummyIPv4AddressOnL2Mode" option for the OpenVPN L2 mode.

src/Cedar/Cedar.c

@@ -1554,6 +1554,8 @@ CEDAR *NewCedar(X *server_x, K *server_k)
 
 	StrCpy(c->OpenVPNDefaultClientOption, sizeof(c->OpenVPNDefaultClientOption), OVPN_DEF_CLIENT_OPTION_STRING);
 
+	c->OpenVPNPushDummyIPv4AddressOnL2Mode = true; // Default true. Override by the config file.
+
 #ifdef	BETA_NUMBER
 	c->Beta = BETA_NUMBER;
 #endif	// BETA_NUMBER

src/Cedar/Cedar.h

@@ -1083,6 +1083,7 @@ typedef struct CEDAR
 	char OpenVPNDefaultClientOption[MAX_SIZE];	// OpenVPN: Default Client Option String
 	bool OpenVPNObfuscation;					// OpenVPN: Obfuscation mode
 	char OpenVPNObfuscationMask[MAX_SIZE];		// OpenVPN: String (mask) for XOR obfuscation
+	bool OpenVPNPushDummyIPv4AddressOnL2Mode;	// OpenVPN: Push a dummy IPv4 address on L2 mode
 } CEDAR;
 
 // Type of CEDAR

src/Cedar/Proto_OpenVPN.c

@@ -2351,6 +2351,18 @@ void OvsRecvPacket(OPENVPN_SERVER *s, LIST *recv_packet_list, UINT protocol)
 									OvsLog(s, se, c, "LP_SET_IPV4_PARAM",
 										ip_client, ip_subnet_mask, ip_defgw, ip_dns1, ip_dns2, ip_wins1, ip_wins2);
 								}
+								else
+								{
+									// OpenVPN L2 mode. To fix the bug of OpenVPN 2.4.6 and particular version of kernel mode TAP driver
+									// on Linux, the TAP device must be up after the OpenVPN client is connected.
+									// However there is no direct push instruction to do so to OpenVPN client.
+									// Therefore we push the dummy IPv4 address (RFC7600) to the OpenVPN client.
+
+									if (s->Cedar->OpenVPNPushDummyIPv4AddressOnL2Mode)
+									{
+										StrCat(option_str, sizeof(option_str), ",ifconfig 192.0.0.8 255.255.255.240");
+									}
+								}
 
 								WriteFifo(c->SslPipe->SslInOut->SendFifo, option_str, StrSize(option_str));
 

src/Cedar/Server.c

@@ -5872,6 +5872,17 @@ void SiLoadServerCfg(SERVER *s, FOLDER *f)
 			}
 		}
 
+		// OpenVPN Push a dummy IPv4 address on L2 mode
+		if (CfgIsItem(f, "OpenVPNPushDummyIPv4AddressOnL2Mode") == false)
+		{
+			// Default enable
+			c->OpenVPNPushDummyIPv4AddressOnL2Mode = true;
+		}
+		else
+		{
+			c->OpenVPNPushDummyIPv4AddressOnL2Mode = CfgGetBool(f, "OpenVPNPushDummyIPv4AddressOnL2Mode");
+		}
+
 		// Disable the NAT-traversal feature
 		s->DisableNatTraversal = CfgGetBool(f, "DisableNatTraversal");
 
@@ -6289,6 +6300,8 @@ void SiWriteServerCfg(FOLDER *f, SERVER *s)
 
 		CfgAddStr(f, "OpenVPNDefaultClientOption", c->OpenVPNDefaultClientOption);
 
+		CfgAddBool(f, "OpenVPNPushDummyIPv4AddressOnL2Mode", c->OpenVPNPushDummyIPv4AddressOnL2Mode);
+
 		if (c->Bridge == false)
 		{
 			OPENVPN_SSTP_CONFIG config;