Index: src/OFDDPSocket.h
==================================================================
--- src/OFDDPSocket.h
+++ src/OFDDPSocket.h
@@ -37,10 +37,15 @@
  * @ref OFSocketAddressMakeAppleTalk to create an address or
  * @ref OFSocketAddressAppleTalkNetwork to get the AppleTalk network,
  * @ref OFSocketAddressAppleTalkNode to get the AppleTalk node and
  * @ref OFSocketAddressAppleTalkPort to get the port (sometimes also called
  * socket number).
+ *
+ * @note On some systems, packets received with the wrong protocol type just
+ *	 get filtered by the kernel, however, on other systems, the packet is
+ *	 queued up and will raise an @ref OFReadFailedException with the
+ *	 @ref errNo set to `ENOMSG` when being received.
  *
  * @warning Even though the OFCopying protocol is implemented, it does *not*
  *	    return an independent copy of the socket, but instead retains it.
  *	    This is so that the socket can be used as a key for a dictionary,
  *	    so context can be associated with a socket. Using a socket in more
@@ -47,10 +52,13 @@
  *	    than one thread at the same time is not thread-safe, even if copy
  *	    was called to create one "instance" for every thread!
  */
 @interface OFDDPSocket: OFDatagramSocket
 {
+#if !defined(OF_MACOS) && !defined(OF_WINDOWS)
+	uint8_t _protocolType;
+#endif
 	OF_RESERVE_IVARS(OFDDPSocket, 4)
 }
 
 /**
  * @brief The delegate for asynchronous operations on the socket.
@@ -66,15 +74,19 @@
  *
  * @param network The network to bind to. 0 means any.
  * @param node The node to bind to. 0 means "this node".
  * @param port The port to bind to. 0 means to pick one and return it via the
  *	       returned socket address.
+ * @param protocolType The DDP protocol type to use. Must not be 0. If you want
+ *		       to use DDP directly and not a protocol built on top of
+ *		       it, use 11 for compatibility with Open Transport.
  * @return The address on which this socket can be reached
  * @throw OFBindDDPSockeFailedException Binding failed
  * @throw OFAlreadyConnectedException The socket is already bound
  */
 - (OFSocketAddress)bindToNetwork: (uint16_t)network
 			    node: (uint8_t)node
-			    port: (uint8_t)port;
+			    port: (uint8_t)port
+		    protocolType: (uint8_t)protocolType;
 @end
 
 OF_ASSUME_NONNULL_END

Index: src/OFDDPSocket.m
==================================================================
--- src/OFDDPSocket.m
+++ src/OFDDPSocket.m
@@ -25,10 +25,11 @@
 #import "OFSocket.h"
 #import "OFSocket+Private.h"
 
 #import "OFAlreadyConnectedException.h"
 #import "OFBindDDPSocketFailedException.h"
+#import "OFInvalidArgumentException.h"
 #import "OFNotOpenException.h"
 #import "OFReadFailedException.h"
 #import "OFWriteFailedException.h"
 
 #ifdef OF_HAVE_NETAT_APPLETALK_H
@@ -42,17 +43,22 @@
 	struct at_addr address, router;
 	unsigned short netStart, netEnd;
 	at_nvestr_t zoneName;
 };
 #endif
+
+#ifndef ATPROTO_BASE
+# define ATPROTO_BASE 0
+#endif
 
 @implementation OFDDPSocket
 @dynamic delegate;
 
 - (OFSocketAddress)bindToNetwork: (uint16_t)network
 			    node: (uint8_t)node
 			    port: (uint8_t)port
+		    protocolType: (uint8_t)protocolType
 {
 #ifdef OF_MACOS
 	const int one = 1;
 	struct ATInterfaceConfig config = { { 0 } };
 #endif
@@ -59,26 +65,31 @@
 	OFSocketAddress address;
 #if SOCK_CLOEXEC == 0 && defined(HAVE_FCNTL_H) && defined(FD_CLOEXEC)
 	int flags;
 #endif
 
+	if (protocolType == 0)
+		@throw [OFInvalidArgumentException exception];
+
 	if (_socket != OFInvalidSocketHandle)
 		@throw [OFAlreadyConnectedException exceptionWithSocket: self];
 
 	address = OFSocketAddressMakeAppleTalk(network, node, port);
 
 #ifdef OF_MACOS
 	if ((_socket = socket(address.sockaddr.at.sat_family,
-	    SOCK_RAW | SOCK_CLOEXEC, 0)) == OFInvalidSocketHandle)
+	    SOCK_RAW | SOCK_CLOEXEC, protocolType)) == OFInvalidSocketHandle)
 #else
 	if ((_socket = socket(address.sockaddr.at.sat_family,
-	    SOCK_DGRAM | SOCK_CLOEXEC, 0)) == OFInvalidSocketHandle)
+	    SOCK_DGRAM | SOCK_CLOEXEC, ATPROTO_BASE + protocolType)) ==
+	    OFInvalidSocketHandle)
 #endif
 		@throw [OFBindDDPSocketFailedException
 		    exceptionWithNetwork: network
 				    node: node
 				    port: port
+			    protocolType: protocolType
 				  socket: self
 				   errNo: OFSocketErrNo()];
 
 	_canBlock = true;
 
@@ -96,10 +107,11 @@
 
 		@throw [OFBindDDPSocketFailedException
 		    exceptionWithNetwork: network
 				    node: node
 				    port: port
+			    protocolType: protocolType
 				  socket: self
 				   errNo: errNo];
 	}
 
 	memset(&address, 0, sizeof(address));
@@ -115,10 +127,11 @@
 
 		@throw [OFBindDDPSocketFailedException
 		    exceptionWithNetwork: network
 				    node: node
 				    port: port
+			    protocolType: protocolType
 				  socket: self
 				   errNo: errNo];
 	}
 
 	if (address.sockaddr.at.sat_family != AF_APPLETALK) {
@@ -127,111 +140,118 @@
 
 		@throw [OFBindDDPSocketFailedException
 		    exceptionWithNetwork: network
 				    node: node
 				    port: port
+			    protocolType: protocolType
 				  socket: self
 				   errNo: EAFNOSUPPORT];
 	}
 
 #ifdef OF_MACOS
-	if (setsockopt(_socket, ATPROTO_NONE, DDP_HDRINCL, &one, sizeof(one)) !=
-	    0 ||
-	    ioctl(_socket, _IOWR('a', 2, struct ATInterfaceConfig), &config) !=
-	    0)
+	if (setsockopt(_socket, ATPROTO_NONE, DDP_STRIPHDR, &one,
+	    sizeof(one)) != 0 || ioctl(_socket, _IOWR('a', 2,
+	    struct ATInterfaceConfig), &config) != 0)
 		@throw [OFBindDDPSocketFailedException
 		    exceptionWithNetwork: network
 				    node: node
 				    port: port
+			    protocolType: protocolType
 				  socket: self
 				   errNo: OFSocketErrNo()];
 
 	OFSocketAddressSetAppleTalkNetwork(&address, config.address.s_net);
 	OFSocketAddressSetAppleTalkNode(&address, config.address.s_node);
 #endif
+
+#if !defined(OF_MACOS) && !defined(OF_WINDOWS)
+	_protocolType = protocolType;
+#endif
 
 	return address;
 }
 
-#ifdef OF_MACOS
+/*
+ * Everybody but macOS and Windows is probably using a netatalk-compatible
+ * implementation, which includes the protocol type as the first byte of the
+ * data instead of considering it part of the header.
+ *
+ * The following overrides prepend the protocol type when sending and compare
+ * and strip it when receiving.
+ *
+ * Unfortunately, the downside of this is that the only way to handle receiving
+ * a packet with the wrong protocol type is to throw an exception with errNo
+ * ENOMSG, while macOS and Windows just filter those out in the kernel.
+ * Returning 0 would mean this is indistinguishable from an empty packet, so it
+ * has to be an exception.
+ */
+#if !defined(OF_MACOS) && !defined(OF_WINDOWS)
 - (size_t)receiveIntoBuffer: (void *)buffer
 		     length: (size_t)length
 		     sender: (OFSocketAddress *)sender
 {
 	ssize_t ret;
-	at_ddp_t header;
+	uint8_t protocolType;
 	struct iovec iov[2] = {
-		{ &header, offsetof(at_ddp_t, type) },
+		{ &protocolType, 1 },
 		{ buffer, length }
+	};
+	struct msghdr msg = {
+		.msg_name = (struct sockaddr *)&sender->sockaddr,
+		.msg_namelen = (socklen_t)sizeof(sender->sockaddr),
+		.msg_iov = iov,
+		.msg_iovlen = 2
 	};
 
 	if (_socket == OFInvalidSocketHandle)
 		@throw [OFNotOpenException exceptionWithObject: self];
 
-	if ((ret = readv(_socket, iov, 2)) < 0)
+	if ((ret = recvmsg(_socket, &msg, 0)) < 0)
 		@throw [OFReadFailedException
 		    exceptionWithObject: self
 			requestedLength: length
 				  errNo: OFSocketErrNo()];
 
-	*sender = OFSocketAddressMakeAppleTalk(
-	    header.src_net[0] << 8 | header.src_net[1], header.src_node,
-	    header.src_socket);
-
-	ret -= offsetof(at_ddp_t, type);
-	if (ret < 0)
-		return 0;
-
-	return ret;
+	if (ret < 1 || protocolType != _protocolType)
+		@throw [OFReadFailedException exceptionWithObject: self
+						  requestedLength: length
+							    errNo: ENOMSG];
+
+	sender->length = msg.msg_namelen;
+	sender->family = OFSocketAddressFamilyAppleTalk;
+
+	return ret - 1;
 }
 
 - (void)sendBuffer: (const void *)buffer
 	    length: (size_t)length
 	  receiver: (const OFSocketAddress *)receiver
 {
-	at_ddp_t header = { 0 };
 	struct iovec iov[2] = {
-		{ &header, offsetof(at_ddp_t, type) },
+		{ &_protocolType, 1 },
 		{ (void *)buffer, length }
 	};
 	struct msghdr msg = {
 		.msg_name = (struct sockaddr *)&receiver->sockaddr,
 		.msg_namelen = receiver->length,
 		.msg_iov = iov,
 		.msg_iovlen = 2
 	};
-	size_t packetLength = length + offsetof(at_ddp_t, type);
-	uint16_t net;
 	ssize_t bytesWritten;
 
 	if (_socket == OFInvalidSocketHandle)
 		@throw [OFNotOpenException exceptionWithObject: self];
 
-	if (packetLength > DDP_DATAGRAM_SIZE)
-		@throw [OFWriteFailedException exceptionWithObject: self
-						   requestedLength: length
-						      bytesWritten: 0
-							     errNo: EMSGSIZE];
-
-	net = OFSocketAddressAppleTalkNetwork(receiver);
-
-	header.length_H = (packetLength >> 8) & 3;
-	header.length_L = packetLength & 0xFF;
-	header.dst_net[0] = net >> 8;
-	header.dst_net[1] = net & 0xFF;
-	header.dst_node = OFSocketAddressAppleTalkNode(receiver);
-	header.dst_socket = OFSocketAddressAppleTalkPort(receiver);
-
 	if ((bytesWritten = sendmsg(_socket, &msg, 0)) < 0)
 		@throw [OFWriteFailedException
 		    exceptionWithObject: self
 			requestedLength: length
 			   bytesWritten: 0
 				  errNo: OFSocketErrNo()];
 
-	if ((size_t)bytesWritten != packetLength) {
-		bytesWritten -= offsetof(at_ddp_t, type);
+	if ((size_t)bytesWritten != length + 1) {
+		bytesWritten--;
 
 		if (bytesWritten < 0)
 			bytesWritten = 0;
 
 		@throw [OFWriteFailedException exceptionWithObject: self

Index: src/exceptions/OFBindDDPSocketFailedException.h
==================================================================
--- src/exceptions/OFBindDDPSocketFailedException.h
+++ src/exceptions/OFBindDDPSocketFailedException.h
@@ -26,11 +26,11 @@
  */
 OF_SUBCLASSING_RESTRICTED
 @interface OFBindDDPSocketFailedException: OFBindSocketFailedException
 {
 	uint16_t _network;
-	uint8_t _node, _port;
+	uint8_t _node, _port, _protocolType;
 }
 
 /**
  * @brief The DDP network on which binding failed.
  */
@@ -44,23 +44,30 @@
 /**
  * @brief The DDP port on which binding failed.
  */
 @property (readonly, nonatomic) uint8_t port;
 
+/**
+ * @brief The DDP protocol type for which binding failed.
+ */
+@property (readonly, nonatomic) uint8_t protocolType;
+
 /**
  * @brief Creates a new, autoreleased bind DDP socket failed exception.
  *
  * @param network The DDP network on which binding failed
  * @param node The DDP node for which binding failed
  * @param port The DDP port on which binding failed
+ * @param protocolType The DDP protocol type for which binding failed.
  * @param socket The socket which could not be bound
  * @param errNo The errno of the error that occurred
  * @return A new, autoreleased bind DDP socket failed exception
  */
 + (instancetype)exceptionWithNetwork: (uint16_t)network
 				node: (uint8_t)node
 				port: (uint8_t)port
+			protocolType: (uint8_t)protocolType
 			      socket: (id)socket
 			       errNo: (int)errNo;
 
 + (instancetype)exceptionWithSocket: (id)socket
 			      errNo: (int)errNo OF_UNAVAILABLE;
@@ -69,19 +76,21 @@
  * @brief Initializes an already allocated bind DDP socket failed exception.
  *
  * @param network The DDP network on which binding failed
  * @param node The DDP node for which binding failed
  * @param port The DDP port on which binding failed
+ * @param protocolType The DDP protocol type for which binding failed.
  * @param socket The socket which could not be bound
  * @param errNo The errno of the error that occurred
  * @return An initialized bind DDP socket failed exception
  */
 - (instancetype)initWithNetwork: (uint16_t)network
 			   node: (uint8_t)node
 			   port: (uint8_t)port
+		   protocolType: (uint8_t)protocolType
 			 socket: (id)socket
 			  errNo: (int)errNo OF_DESIGNATED_INITIALIZER;
 
 - (instancetype)initWithSocket: (id)socket errNo: (int)errNo OF_UNAVAILABLE;
 @end
 
 OF_ASSUME_NONNULL_END

Index: src/exceptions/OFBindDDPSocketFailedException.m
==================================================================
--- src/exceptions/OFBindDDPSocketFailedException.m
+++ src/exceptions/OFBindDDPSocketFailedException.m
@@ -19,25 +19,28 @@
 #import "OFData.h"
 #import "OFString.h"
 
 @implementation OFBindDDPSocketFailedException
 @synthesize network = _network, node = _node, port = _port;
+@synthesize protocolType = _protocolType;
 
 + (instancetype)exceptionWithSocket: (id)sock errNo: (int)errNo
 {
 	OF_UNRECOGNIZED_SELECTOR
 }
 
 + (instancetype)exceptionWithNetwork: (uint16_t)network
 				node: (uint8_t)node
 				port: (uint8_t)port
+			protocolType: (uint8_t)protocolType
 			      socket: (id)sock
 			       errNo: (int)errNo
 {
 	return [[[self alloc] initWithNetwork: network
 					 node: node
 					 port: port
+				 protocolType: protocolType
 				       socket: sock
 					errNo: errNo] autorelease];
 }
 
 - (instancetype)initWithSocket: (id)sock errNo: (int)errNo
@@ -46,19 +49,21 @@
 }
 
 - (instancetype)initWithNetwork: (uint16_t)network
 			   node: (uint8_t)node
 			   port: (uint8_t)port
+		   protocolType: (uint8_t)protocolType
 			 socket: (id)sock
 			  errNo: (int)errNo
 {
 	self = [super initWithSocket: sock errNo: errNo];
 
 	@try {
 		_network = network;
 		_node = node;
 		_port = port;
+		_protocolType = protocolType;
 	} @catch (id e) {
 		[self release];
 		@throw e;
 	}
 
@@ -67,9 +72,11 @@
 
 - (OFString *)description
 {
 	return [OFString stringWithFormat:
 	    @"Binding to port %" @PRIx8 @" of node %" @PRIx8 @" on network "
-	    @"%" PRIx16 @" failed in socket of type %@: %@",
-	    _port, _node, _network, [_socket class], OFStrError(_errNo)];
+	    @"%" PRIx16 @" with protocol type " @PRIx8 @" failed in socket of "
+	    @"type %@: %@",
+	    _port, _node, _network, _protocolType, [_socket class],
+	    OFStrError(_errNo)];
 }
 @end

Index: tests/OFDDPSocketTests.m
==================================================================
--- tests/OFDDPSocketTests.m
+++ tests/OFDDPSocketTests.m
@@ -31,24 +31,29 @@
 
 	TEST(@"+[socket]", (sock = [OFDDPSocket socket]))
 
 	@try {
 		TEST(@"-[bindToNetwork:node:port:]",
-		    R(address1 = [sock bindToNetwork: 0 node: 0 port: 0]))
+		    R(address1 = [sock bindToNetwork: 0
+						node: 0
+						port: 0
+					protocolType: 11]))
 	} @catch (OFBindSocketFailedException *e) {
 		switch (e.errNo) {
 		case EAFNOSUPPORT:
 			[OFStdOut setForegroundColor: [OFColor lime]];
 			[OFStdOut writeLine:
-			    @"\r[OFDDPSocket] -[bindToNetwork:node:port:] "
-			    @"AppleTalk unsupported, skipping tests"];
+			    @"\r[OFDDPSocket] -[bindToNetwork:node:port:"
+			    @"protocolType:] AppleTalk unsupported, skipping "
+			    @"tests"];
 			break;
 		case EADDRNOTAVAIL:
 			[OFStdOut setForegroundColor: [OFColor lime]];
 			[OFStdOut writeLine:
-			    @"\r[OFDDPSocket] -[bindToNetwork:node:port:] "
-			    @"AppleTalk not configured, skipping tests"];
+			    @"\r[OFDDPSocket] -[bindToNetwork:node:port:"
+			    @"protocolType:] AppleTalk not configured, "
+			    @"skipping tests"];
 			break;
 		default:
 			@throw e;
 		}