===================================================================
RCS file: /cvsrepo/anoncvs/cvs/src/usr.bin/ssh/PROTOCOL,v
retrieving revision 1.6
retrieving revision 1.7
diff -u -r1.6 -r1.7
--- src/usr.bin/ssh/PROTOCOL	2008/06/10 22:15:23	1.6
+++ src/usr.bin/ssh/PROTOCOL	2008/06/12 05:15:41	1.7
@@ -84,8 +84,69 @@
 Note that this is not a general defence against compromised clients
 (that is impossible), but it thwarts a simple attack.
 
-5. sftp: Reversal of arguments to SSH_FXP_SYMLINK
+5. connection: Tunnel forward extension "tun@openssh.com"
 
+OpenSSH supports layer 2 and layer 3 tunneling via the "tun@openssh.com"
+channel type. This channel type supports forwarding of network packets
+with datagram boundaries entact between endpoints equipped with 
+interfaces like the BSD tun(4) device. Tunnel forwarding channels are
+requested by the client with the following packet:
+
+	byte		SSH_MSG_CHANNEL_OPEN
+	string		"tun@openssh.com"
+	uint32		sender channel
+	uint32		initial window size
+	uint32		maximum packet size
+	uint32		tunnel mode
+	uint32		remote unit number
+
+The "tunnel mode" parameter specifies whether the tunnel should forward
+layer 2 frames or layer 3 packets. It may take one of the following values:
+
+	SSH_TUNMODE_POINTOPOINT  1		/* layer 3 packets */
+	SSH_TUNMODE_ETHERNET     2		/* layer 2 frames */
+
+The "tunnel unit number" specifies the remote interface number, or may
+be zero to allow the server to automatically chose an interface. A server
+that is not willing to open a client-specified unit should refuse the
+request with a SSH_MSG_CHANNEL_OPEN_FAILURE error. On successful open,
+the server should reply with SSH_MSG_CHANNEL_OPEN_SUCCESS.
+
+Once established the client and server may exchange packet or frames
+over the tunnel channel by encapsulating them in SSH protocol strings
+and sending them as channel data. This ensures that packet boundaries
+are kept intact. Specifically, packets are transmitted using normal
+SSH_MSG_CHANNEL_DATA packets:
+
+	byte		SSH_MSG_CHANNEL_DATA
+	uint32		recipient channel
+	string		data
+
+The contents of the "data" field for layer 3 packets is:
+
+	uint32			packet length
+	uint32			address family
+	byte[packet length - 4]	packet data
+
+The "address family" field identifies the type of packet in the message.
+It may be one of:
+
+	SSH_TUN_AF_INET		2		/* IPv4 */
+	SSH_TUN_AF_INET6	24		/* IPv6 */
+
+The "packet data" field consists of the IPv4/IPv6 datagram itself
+without any link layer header.
+
+The contents of the "data" field for layer 3 packets is:
+
+	uint32			packet length
+	byte[packet length]	frame
+
+The "frame" field contains an IEEE 802.3 ethernet frame, including
+header.
+
+6. sftp: Reversal of arguments to SSH_FXP_SYMLINK
+
 When OpenSSH's sftp-server was implemented, the order of the arguments
 to the SSH_FXP_SYMLINK method was inadvertendly reversed. Unfortunately,
 the reversal was not noticed until the server was widely deployed. Since
@@ -97,7 +158,7 @@
 	string		targetpath
 	string		linkpath
 
-6. sftp: Server extension announcement in SSH_FXP_VERSION
+7. sftp: Server extension announcement in SSH_FXP_VERSION
 
 OpenSSH's sftp-server lists the extensions it supports using the
 standard extension announcement mechanism in the SSH_FXP_VERSION server
@@ -118,7 +179,7 @@
 extension with multiple versions (though this is unlikely). Clients MUST
 check the version number before attemping to use the extension.
 
-7. sftp: Extension request "posix-rename@openssh.com"
+8. sftp: Extension request "posix-rename@openssh.com"
 
 This operation provides a rename operation with POSIX semantics, which
 are different to those provided by the standard SSH_FXP_RENAME in
@@ -135,7 +196,7 @@
 This extension is advertised in the SSH_FXP_VERSION hello with version
 "1".
 
-8. sftp: Extension requests "statvfs@openssh.com" and
+9. sftp: Extension requests "statvfs@openssh.com" and
          "fstatvfs@openssh.com"
 
 These requests correspond to the statvfs and fstatvfs POSIX system
@@ -176,5 +237,4 @@
 This extension is advertised in the SSH_FXP_VERSION hello with version
 "2".
 
-$OpenBSD: PROTOCOL,v 1.6 2008/06/10 22:15:23 djm Exp $
-
+$OpenBSD: PROTOCOL,v 1.7 2008/06/12 05:15:41 djm Exp $