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PACKET DESIGN DOES NOT WARRANT, GUARANTEE, .\" OR MAKE ANY REPRESENTATIONS REGARDING THE USE OF, OR THE RESULTS .\" OF THE USE OF THIS SOFTWARE IN TERMS OF ITS CORRECTNESS, ACCURACY, .\" RELIABILITY OR OTHERWISE. IN NO EVENT SHALL PACKET DESIGN BE .\" LIABLE FOR ANY DAMAGES RESULTING FROM OR ARISING OUT OF ANY USE .\" OF THIS SOFTWARE, INCLUDING WITHOUT LIMITATION, ANY DIRECT, .\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR CONSEQUENTIAL .\" DAMAGES, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES, LOSS OF .\" USE, DATA OR PROFITS, HOWEVER CAUSED AND UNDER ANY THEORY OF .\" LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF .\" THE USE OF THIS SOFTWARE, EVEN IF PACKET DESIGN IS ADVISED OF .\" THE POSSIBILITY OF SUCH DAMAGE. .\" .\" Author: Archie Cobbs .\" .\" $FreeBSD$ .\" .Dd November 13, 2012 .Dt NG_L2TP 4 .Os .Sh NAME .Nm ng_l2tp .Nd L2TP protocol netgraph node type .Sh SYNOPSIS .In sys/types.h .In netgraph/ng_l2tp.h .Sh DESCRIPTION The .Nm l2tp node type implements the encapsulation layer of the L2TP protocol as described in RFC 2661. This includes adding the L2TP packet header for outgoing packets and verifying and removing it for incoming packets. The node maintains the L2TP sequence number state and handles control session packet acknowledgment and retransmission. .Sh HOOKS The .Nm l2tp node type supports the following hooks: .Bl -tag -width ".Va session_hhhh" .It Va lower L2TP frames. .It Va ctrl Control packets. .It Va session_hhhh Session 0xhhhh data packets. .El .Pp L2TP control and data packets are transmitted to, and received from, the L2TP peer via the .Dv lower hook. Typically this hook would be connected to the .Dv "inet/dgram/udp" hook of an .Xr ng_ksocket 4 node for L2TP over UDP. .Pp The .Dv ctrl hook connects to the local L2TP management entity. L2TP control messages (without any L2TP headers) are transmitted and received on this hook. Messages written to this hook are guaranteed to be delivered to the peer reliably, in order, and without duplicates. .Pp Packets written to the .Dv ctrl hook must contain a two byte session ID prepended to the frame (in network order). This session ID is copied to the outgoing L2TP header. Similarly, packets read from the .Dv ctrl hook will have the received session ID prepended. .Pp Once an L2TP session has been created, the corresponding session hook may be used to transmit and receive the session's data frames: for the session with session ID .Dv 0xabcd , the hook is named .Dv session_abcd . .Sh CONTROL MESSAGES This node type supports the generic control messages, plus the following: .Bl -tag -width foo .It Dv NGM_L2TP_SET_CONFIG Pq Ic setconfig This command updates the configuration of the node. It takes a .Vt "struct ng_l2tp_config" as an argument: .Bd -literal /* Configuration for a node */ struct ng_l2tp_config { u_char enabled; /* enables traffic flow */ u_char match_id; /* tunnel id must match 'tunnel_id' */ uint16_t tunnel_id; /* local tunnel id */ uint16_t peer_id; /* peer's tunnel id */ uint16_t peer_win; /* peer's max recv window size */ uint16_t rexmit_max; /* max retransmits before failure */ uint16_t rexmit_max_to; /* max delay between retransmits */ }; .Ed .Pp The .Va enabled field enables packet processing. Each time this field is changed back to zero the sequence number state is reset. In this way, reuse of a node is possible. .Pp The .Va tunnel_id field configures the local tunnel ID for the control connection. The .Va match_id field determines how incoming L2TP packets with a tunnel ID field different from .Va tunnel_id are handled. If .Va match_id is non-zero, they will be dropped; otherwise, they will be dropped only if the tunnel ID is non-zero. Typically .Va tunnel_id is set to the local tunnel ID as soon as it is known and .Va match_id is set to non-zero after receipt of the SCCRP or SCCCN control message. .Pp The peer's tunnel ID should be set in .Va peer_id as soon as it is learned, typically after receipt of a SCCRQ or SCCRP control message. This value is copied into the L2TP header for outgoing packets. .Pp The .Va peer_win field should be set from the .Dq "Receive Window Size" AVP received from the peer. The default value for this field is one; zero is an invalid value. As long as .Va enabled is non-zero, this value may not be decreased. .Pp The .Va rexmit_max and .Va rexmit_max_to fields configure packet retransmission. .Va rexmit_max_to is the maximum retransmission delay between packets, in seconds. The retransmit delay will start at a small value and increase exponentially up to this limit. The .Va rexmit_max sets the maximum number of times a packet will be retransmitted without being acknowledged before a failure condition is declared. Once a failure condition is declared, each additional retransmission will cause the .Nm l2tp node to send a .Dv NGM_L2TP_ACK_FAILURE Pq Ic ackfailure control message back to the node that sent the last .Dv NGM_L2TP_SET_CONFIG . Appropriate action should then be taken to shutdown the control connection. .It Dv NGM_L2TP_GET_CONFIG Pq Ic getconfig Returns the current configuration as a .Vt "struct ng_l2tp_config" . .It Dv NGM_L2TP_SET_SESS_CONFIG Pq Ic setsessconfig This control message configures a single data session. The corresponding hook must already be connected before sending this command. The argument is a .Vt "struct ng_l2tp_sess_config" : .Bd -literal /* Configuration for a session hook */ struct ng_l2tp_sess_config { uint16_t session_id; /* local session id */ uint16_t peer_id; /* peer's session id */ u_char control_dseq; /* whether we control data sequencing */ u_char enable_dseq; /* whether to enable data sequencing */ u_char include_length; /* whether to include length field */ }; .Ed .Pp The .Va session_id and .Va peer_id fields configure the local and remote session IDs, respectively. .Pp The .Va control_dseq and .Va enable_dseq fields determine whether sequence numbers are used with L2TP data packets. If .Va enable_dseq is zero, then no sequence numbers are sent and incoming sequence numbers are ignored. Otherwise, sequence numbers are included on outgoing packets and checked on incoming packets. .Pp If .Va control_dseq is non-zero, then the setting of .Va enable_dseq will never change except by another .Dv NGM_L2TP_SET_SESS_CONFIG control message. If .Va control_dseq is zero, then the peer controls whether sequence numbers are used: if an incoming L2TP data packet contains sequence numbers, .Va enable_dseq is set to one, and conversely if an incoming L2TP data packet does not contain sequence numbers, .Va enable_dseq is set to zero. The current value of .Va enable_dseq is always accessible via the .Dv NGM_L2TP_GET_SESS_CONFIG control message (see below). Typically an LNS would set .Va control_dseq to one while a LAC would set .Va control_dseq to zero (if the Sequencing Required AVP were not sent), thus giving control of data packet sequencing to the LNS. .Pp The .Va include_length field determines whether the L2TP header length field is included in outgoing L2TP data packets. For incoming packets, the L2TP length field is always checked when present. .It Dv NGM_L2TP_GET_SESS_CONFIG Pq Ic getsessconfig This command takes a two byte session ID as an argument and returns the current configuration for the corresponding data session as a .Vt "struct ng_l2tp_sess_config" . The corresponding session hook must be connected. .It Dv NGM_L2TP_GET_STATS Pq Ic getstats This command returns a .Vt "struct ng_l2tp_stats" containing statistics of the L2TP tunnel. .It Dv NGM_L2TP_CLR_STATS Pq Ic clrstats This command clears the statistics for the L2TP tunnel. .It Dv NGM_L2TP_GETCLR_STATS Pq Ic getclrstats Same as .Dv NGM_L2TP_GET_STATS , but also atomically clears the statistics as well. .It Dv NGM_L2TP_GET_SESSION_STATS Pq Ic getsessstats This command takes a two byte session ID as an argument and returns a .Vt "struct ng_l2tp_session_stats" containing statistics for the corresponding data session. The corresponding session hook must be connected. .It Dv NGM_L2TP_CLR_SESSION_STATS Pq Ic clrsessstats This command takes a two byte session ID as an argument and clears the statistics for that data session. The corresponding session hook must be connected. .It Dv NGM_L2TP_GETCLR_SESSION_STATS Pq Ic getclrsessstats Same as .Dv NGM_L2TP_GET_SESSION_STATS , but also atomically clears the statistics as well. .It Dv NGM_L2TP_SET_SEQ Pq Ic setsequence This command sets the sequence numbers of a not yet enabled node. It takes a .Vt "struct ng_l2tp_seq_config" as argument, where .Va xack and .Va nr respectively .Va ns and .Va rack must be the same. This option is particularly useful if one receives and processes the first packet entirely in userspace and wants to hand over further processing to the node. .El .Sh SHUTDOWN This node shuts down upon receipt of a .Dv NGM_SHUTDOWN control message, or when all hooks have been disconnected. .Sh SEE ALSO .Xr netgraph 4 , .Xr ng_ksocket 4 , .Xr ng_ppp 4 , .Xr ng_pptpgre 4 , .Xr ngctl 8 .Rs .%A W. Townsley .%A A. Valencia .%A A. Rubens .%A G. Pall .%A G. Zorn .%A B. Palter .%T "Layer Two Tunneling Protocol L2TP" .%O RFC 2661 .Re .Sh HISTORY The .Nm l2tp node type was developed at Packet Design, LLC, .Pa http://www.packetdesign.com/ . .Sh AUTHORS .An Archie Cobbs Aq archie@packetdesign.com