diff --git a/ChangeLog b/ChangeLog
index 94e3f6e5a..ad7cd52fa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -16,6 +16,10 @@
    - stevesk@cvs.openbsd.org 2005/12/31 01:38:45
      [ssh.1]
      document -MM; ok djm@
+ - (djm) [openbsd-compat/port-tun.c openbsd-compat/port-tun.h configure.ac]
+   [serverloop.c ssh.c openbsd-compat/Makefile.in]
+   [openbsd-compat/openbsd-compat.h] Implement tun(4) forwarding 
+   compatability support for Linux, diff from reyk@
 
 20051229
  - (tim) [buildpkg.sh.in] grep for $SSHDUID instead of $SSHDGID on /etc/passwd
@@ -3571,4 +3575,4 @@
    - (djm) Trim deprecated options from INSTALL. Mention UsePAM
    - (djm) Fix quote handling in sftp; Patch from admorten AT umich.edu
 
-$Id: ChangeLog,v 1.4056 2005/12/31 05:23:15 djm Exp $
+$Id: ChangeLog,v 1.4057 2005/12/31 05:33:36 djm Exp $
diff --git a/configure.ac b/configure.ac
index 9325c4364..64046759f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,4 +1,4 @@
-# $Id: configure.ac,v 1.316 2005/12/19 06:40:40 dtucker Exp $
+# $Id: configure.ac,v 1.317 2005/12/31 05:33:37 djm Exp $
 #
 # Copyright (c) 1999-2004 Damien Miller
 #
@@ -326,6 +326,9 @@ main() { if (NSVersionOfRunTimeLibrary("System") >= (60 << 16))
 			[Define if cmsg_type is not passed correctly])
 		;;
 	esac
+	AC_DEFINE(SSH_TUN_LINUX, 1, [Open tunnel devices the Linux tun/tap way])
+	AC_DEFINE(SSH_TUN_COMPAT_AF, 1, [Use tunnel device compatibility to OpenBSD])
+	AC_DEFINE(SSH_TUN_PREPEND_AF, 1, [Prepend the address family to IP tunnel traffic])
 	;;
 mips-sony-bsd|mips-sony-newsos4)
 	AC_DEFINE(NEED_SETPRGP, 1, [Need setpgrp to acquire controlling tty])
diff --git a/openbsd-compat/Makefile.in b/openbsd-compat/Makefile.in
index 89ac6cdaf..3a8703bc1 100644
--- a/openbsd-compat/Makefile.in
+++ b/openbsd-compat/Makefile.in
@@ -1,4 +1,4 @@
-# $Id: Makefile.in,v 1.36 2005/11/24 08:58:21 djm Exp $
+# $Id: Makefile.in,v 1.37 2005/12/31 05:33:37 djm Exp $
 
 sysconfdir=@sysconfdir@
 piddir=@piddir@
@@ -20,7 +20,7 @@ OPENBSD=base64.o basename.o bindresvport.o daemon.o dirname.o getcwd.o getgroupl
 
 COMPAT=bsd-arc4random.o bsd-asprintf.o bsd-closefrom.o bsd-cray.o bsd-cygwin_util.o bsd-getpeereid.o bsd-misc.o bsd-nextstep.o bsd-openpty.o bsd-snprintf.o bsd-waitpid.o fake-rfc2553.o openssl-compat.o xmmap.o xcrypt.o
 
-PORTS=port-irix.o port-aix.o port-uw.o
+PORTS=port-irix.o port-aix.o port-uw.o port-tun.o
 
 .c.o:
 	$(CC) $(CFLAGS) $(CPPFLAGS) -c $<
diff --git a/openbsd-compat/openbsd-compat.h b/openbsd-compat/openbsd-compat.h
index fe0c36dcd..1a3027353 100644
--- a/openbsd-compat/openbsd-compat.h
+++ b/openbsd-compat/openbsd-compat.h
@@ -1,4 +1,4 @@
-/* $Id: openbsd-compat.h,v 1.32 2005/11/24 08:58:21 djm Exp $ */
+/* $Id: openbsd-compat.h,v 1.33 2005/12/31 05:33:37 djm Exp $ */
 
 /*
  * Copyright (c) 1999-2003 Damien Miller.  All rights reserved.
@@ -186,5 +186,6 @@ char *shadow_pw(struct passwd *pw);
 #include "port-irix.h"
 #include "port-aix.h"
 #include "port-uw.h"
+#include "port-tun.h"
 
 #endif /* _OPENBSD_COMPAT_H */
diff --git a/openbsd-compat/port-tun.c b/openbsd-compat/port-tun.c
new file mode 100644
index 000000000..479b46b7a
--- /dev/null
+++ b/openbsd-compat/port-tun.c
@@ -0,0 +1,155 @@
+/*
+ * Copyright (c) 2005 Reyk Floeter <reyk@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "includes.h"
+
+#include "log.h"
+#include "misc.h"
+#include "bufaux.h"
+
+/*
+ * This is the portable version of the SSH tunnel forwarding, it
+ * uses some preprocessor definitions for various platform-specific
+ * settings.
+ *
+ * SSH_TUN_LINUX	Use the (newer) Linux tun/tap device
+ * SSH_TUN_COMPAT_AF	Translate the OpenBSD address family
+ * SSH_TUN_PREPEND_AF	Prepend/remove the address family
+ */
+
+/*
+ * System-specific tunnel open function
+ */
+
+#if defined(SSH_TUN_LINUX)
+#include <linux/if_tun.h>
+
+int
+sys_tun_open(int tun, int mode)
+{
+	struct ifreq ifr;
+	int fd = -1;
+	const char *name = NULL;
+
+	if ((fd = open("/dev/net/tun", O_RDWR)) == -1) {
+		debug("%s: failed to open tunnel control interface: %s",
+		    __func__, strerror(errno));
+		return (-1);
+	}
+
+	bzero(&ifr, sizeof(ifr));	
+
+	if (mode == SSH_TUNMODE_ETHERNET) {
+		ifr.ifr_flags = IFF_TAP;
+		name = "tap%d";
+	} else {
+		ifr.ifr_flags = IFF_TUN;
+		name = "tun%d";
+	}
+	ifr.ifr_flags |= IFF_NO_PI;
+
+	if (tun != SSH_TUNID_ANY) {
+		if (tun > SSH_TUNID_MAX) {
+			debug("%s: invalid tunnel id %x: %s", __func__,
+			    tun, strerror(errno));
+			goto failed;
+		}
+		snprintf(ifr.ifr_name, sizeof(ifr.ifr_name), name, tun);
+	}
+
+	if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
+		debug("%s: failed to configure tunnel (mode %d): %s", __func__,
+		    mode, strerror(errno));
+		goto failed;
+	}
+
+	if (tun == SSH_TUNID_ANY)
+		debug("%s: tunnel mode %d fd %d", __func__, mode, fd);
+	else
+		debug("%s: %s mode %d fd %d", __func__, ifr.ifr_name, mode, fd);
+
+	return (fd);
+
+ failed:
+	close(fd);
+	return (-1);
+}
+#endif /* SSH_TUN_LINUX */
+
+/*
+ * System-specific channel filters
+ */
+
+#if defined(SSH_TUN_FILTER)
+#define OPENBSD_AF_INET		2
+#define OPENBSD_AF_INET6	24
+
+int
+sys_tun_infilter(struct Channel *c, char *buf, int len)
+{
+#if defined(SSH_TUN_PREPEND_AF)
+	char rbuf[CHAN_RBUF];
+#endif
+	u_int32_t *af;
+	char *ptr = buf;
+
+#if defined(SSH_TUN_PREPEND_AF)
+	if (len > (int)(sizeof(rbuf) - sizeof(*af)))
+		return (-1);
+	ptr = (char *)&rbuf[0];
+	bcopy(buf, ptr + sizeof(u_int32_t), len);
+	len += sizeof(u_int32_t);
+#endif
+
+#if defined(SSH_TUN_COMPAT_AF)
+	if (len < (int)sizeof(u_int32_t))
+		return (-1);
+
+	af = (u_int32_t *)ptr;
+	if (*af == htonl(AF_INET6))
+		*af = htonl(OPENBSD_AF_INET6);
+	else
+		*af = htonl(OPENBSD_AF_INET);
+#endif
+	buffer_put_string(&c->input, ptr, len);
+	return (0);
+}
+
+u_char *
+sys_tun_outfilter(struct Channel *c, u_char **data, u_int *dlen)
+{
+	u_char *buf;
+	u_int32_t *af;
+
+	*data = buffer_get_string(&c->output, dlen);
+	if (*dlen < sizeof(*af))
+		return (NULL);
+	buf = *data;
+
+#if defined(SSH_TUN_PREPEND_AF)
+	*dlen -= sizeof(u_int32_t);
+	buf = *data + sizeof(u_int32_t);
+#elif defined(SSH_TUN_COMPAT_AF)
+	af = ntohl(*(u_int32_t *)buf);
+	if (*af == OPENBSD_AF_INET6)
+		*af = htonl(AF_INET6);
+	else
+		*af = htonl(AF_INET);
+#endif
+
+	return (buf);
+}
+#endif /* SSH_TUN_FILTER */
diff --git a/openbsd-compat/port-tun.h b/openbsd-compat/port-tun.h
new file mode 100644
index 000000000..942610c6d
--- /dev/null
+++ b/openbsd-compat/port-tun.h
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2005 Reyk Floeter <reyk@openbsd.org>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef _PORT_TUN_H
+#define _PORT_TUN_H
+
+#include "channels.h"
+
+#if defined(SSH_TUN_LINUX)
+# define CUSTOM_SYS_TUN_OPEN
+int	  sys_tun_open(int, int);
+#endif
+
+#if defined(SSH_TUN_COMPAT_AF) || defined(SSH_TUN_PREPEND_AF)
+# define SSH_TUN_FILTER
+int	 sys_tun_infilter(struct Channel *, char *, int);
+u_char	*sys_tun_outfilter(struct Channel *, u_char **, u_int *);
+#endif
+
+#endif
diff --git a/serverloop.c b/serverloop.c
index a575ce0d1..3d8e7cfb5 100644
--- a/serverloop.c
+++ b/serverloop.c
@@ -947,6 +947,11 @@ server_request_tun(void)
 	c = channel_new("tun", SSH_CHANNEL_OPEN, sock, sock, -1,
 	    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT, 0, "tun", 1);
 	c->datagram = 1;
+#if defined(SSH_TUN_FILTER)
+	if (mode == SSH_TUNMODE_POINTOPOINT)
+		channel_register_filter(c->self, sys_tun_infilter,
+		    sys_tun_outfilter);
+#endif
 
  done:
 	if (c == NULL)
diff --git a/ssh.c b/ssh.c
index cdfc91633..3940dabfd 100644
--- a/ssh.c
+++ b/ssh.c
@@ -1079,6 +1079,11 @@ ssh_session2_setup(int id, void *arg)
 			    CHAN_TCP_WINDOW_DEFAULT, CHAN_TCP_PACKET_DEFAULT,
 			    0, "tun", 1);
 			c->datagram = 1;
+#if defined(SSH_TUN_FILTER)
+			if (options.tun_open == SSH_TUNMODE_POINTOPOINT)
+				channel_register_filter(c->self, sys_tun_infilter,
+				    sys_tun_outfilter);
+#endif
 			packet_start(SSH2_MSG_CHANNEL_OPEN);
 			packet_put_cstring("tun@openssh.com");
 			packet_put_int(c->self);