From 49e90d11452e4864ff1d0f9ed1ad19d42eb7dae1 Mon Sep 17 00:00:00 2001 From: Damien Miller Date: Thu, 12 Jun 2008 05:15:42 +0000 Subject: document tun@openssh.com forwarding method --- usr.bin/ssh/PROTOCOL | 72 +++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 66 insertions(+), 6 deletions(-) (limited to 'usr.bin') diff --git a/usr.bin/ssh/PROTOCOL b/usr.bin/ssh/PROTOCOL index 76e6adb4b89..08b16dc1679 100644 --- a/usr.bin/ssh/PROTOCOL +++ b/usr.bin/ssh/PROTOCOL @@ -84,7 +84,68 @@ connection. 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, @@ -97,7 +158,7 @@ SSH_FXP_SYMLINK as follows: 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 @@ ever changed in an incompatible way. The server MAY advertise the same 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 @@ rename(oldpath, newpath) and will respond with a SSH_FXP_STATUS message. 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 @@ The values of the f_flag bitmask are as follows: 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 $ -- cgit v1.2.3