5b63f751da
for L2TP tunnel statistics (which do not take an argument sessionID). Reviewed by: archie Approved by: pjd (mentor)
330 lines
10 KiB
Groff
330 lines
10 KiB
Groff
.\" Copyright (c) 2001-2002 Packet Design, LLC.
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.\" use and redistribution of this software, in source or object code
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.\" THE USE OF THIS SOFTWARE, EVEN IF PACKET DESIGN IS ADVISED OF
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.\" THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" Author: Archie Cobbs <archie@FreeBSD.org>
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 2, 2004
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.Dt NG_L2TP 4
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.Os
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.Sh NAME
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.Nm ng_l2tp
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.Nd L2TP protocol netgraph node type
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.Sh SYNOPSIS
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.In netgraph/ng_l2tp.h
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.Sh DESCRIPTION
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The
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.Nm l2tp
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node type implements the encapsulation layer of the L2TP protocol
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as described in RFC 2661.
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This includes adding the L2TP packet header for outgoing packets
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and verifying and removing it for incoming packets.
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The node maintains the L2TP sequence number state and handles
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control session packet acknowledgment and retransmission.
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.Sh HOOKS
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The
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.Nm l2tp
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node type supports the following hooks:
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.Pp
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.Bl -tag -compact -offset indent -width ".Dv session_hhhh"
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.It Dv lower
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L2TP frames.
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.It Dv ctrl
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Control packets.
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.It Dv session_hhhh
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Session 0xhhhh data packets.
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.El
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.Pp
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L2TP control and data packets are transmitted to, and received from,
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the L2TP peer via the
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.Dv lower
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hook.
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Typically this hook would be connected to the
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.Dv "inet/dgram/udp"
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hook of an
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.Xr ng_ksocket 4
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node for L2TP over UDP.
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.Pp
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The
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.Dv ctrl
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hook connects to the local L2TP management entity.
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L2TP control messages (without any L2TP headers) are transmitted
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and received on this hook.
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Messages written to this hook are guaranteed to be delivered to the
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peer reliably, in order, and without duplicates.
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.Pp
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Packets written to the
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.Dv ctrl
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hook must contain a two byte session ID prepended to the frame
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(in network order).
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This session ID is copied to the outgoing L2TP header.
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Similarly, packets read from the
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.Dv ctrl
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hook will have the received session ID prepended.
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.Pp
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Once an L2TP session has been created, the corresponding session
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hook may be used to transmit and receive the session's data frames:
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for the session with session ID
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.Dv 0xabcd ,
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the hook is named
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.Dv session_abcd .
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.Sh CONTROL MESSAGES
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This node type supports the generic control messages, plus the following:
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.Bl -tag -width indent
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.It Dv NGM_L2TP_SET_CONFIG
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This command updates the configuration of the node.
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It takes a
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.Vt "struct ng_l2tp_config"
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as an argument:
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.Bd -literal
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/* Configuration for a node */
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struct ng_l2tp_config {
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u_char enabled; /* enables traffic flow */
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u_char match_id; /* tunnel id must match 'tunnel_id' */
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u_int16_t tunnel_id; /* local tunnel id */
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u_int16_t peer_id; /* peer's tunnel id */
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u_int16_t peer_win; /* peer's max recv window size */
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u_int16_t rexmit_max; /* max retransmits before failure */
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u_int16_t rexmit_max_to; /* max delay between retransmits */
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};
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.Ed
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.Pp
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The
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.Va enabled
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field enables packet processing.
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Each time this field is changed back to zero the sequence
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number state is reset.
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In this way, reuse of a node is possible.
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.Pp
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The
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.Va tunnel_id
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field configures the local tunnel ID for the control connection.
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The
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.Va match_id
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field determines how incoming L2TP packets with a tunnel ID
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field different from
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.Va tunnel_id
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are handled.
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If
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.Va match_id
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is non-zero, they will be dropped; otherwise, they will be dropped
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only if the tunnel ID is non-zero.
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Typically
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.Va tunnel_id
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is set to the local tunnel ID as soon as it is known and
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.Va match_id
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is set to non-zero after receipt of the SCCRP or SCCCN control message.
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.Pp
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The peer's tunnel ID should be set in
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.Va peer_id
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as soon as it is learned, typically after receipt of a SCCRQ or SCCRP
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control message.
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This value is copied into the L2TP header for outgoing packets.
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.Pp
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The
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.Va peer_win
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field should be set from the
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.Dq "Receive Window Size"
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AVP received from the peer.
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The default value for this field is one; zero is an invalid value.
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As long as
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.Va enabled
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is non-zero, this value may not be decreased.
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.Pp
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The
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.Va rexmit_max
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and
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.Va rexmit_max_to
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fields configure packet retransmission.
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.Va rexmit_max_to
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is the maximum retransmission delay between packets, in seconds.
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The retransmit delay will start at a small value and increase
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exponentially up to this limit.
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The
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.Va rexmit_max
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sets the maximum number of times a packet will be retransmitted
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without being acknowledged before a failure condition is declared.
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Once a failure condition is declared, each additional retransmission
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will cause the
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.Nm l2tp
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node to send a
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.Dv NGM_L2TP_ACK_FAILURE
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control message back to the node that sent the last
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.Dv NGM_L2TP_SET_CONFIG .
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Appropriate action should then be taken to shutdown the control connection.
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.It Dv NGM_L2TP_GET_CONFIG
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Returns the current configuration as a
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.Vt "struct ng_l2tp_config" .
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.It Dv NGM_L2TP_SET_SESS_CONFIG
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This control message configures a single data session.
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The corresponding hook must already be connected before sending this command.
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The argument is a
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.Vt "struct ng_l2tp_sess_config" :
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.Bd -literal
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/* Configuration for a session hook */
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struct ng_l2tp_sess_config {
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u_int16_t session_id; /* local session id */
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u_int16_t peer_id; /* peer's session id */
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u_char control_dseq; /* we control data sequencing? */
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u_char enable_dseq; /* enable data sequencing? */
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u_char include_length; /* include length field? */
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};
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.Ed
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.Pp
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The
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.Va session_id
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and
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.Va peer_id
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fields configure the local and remote session IDs, respectively.
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.Pp
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The
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.Va control_dseq
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and
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.Va enable_dseq
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fields determine whether sequence numbers are used with L2TP data packets.
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If
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.Va enable_dseq
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is zero, then no sequence numbers are sent and incoming sequence numbers
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are ignored.
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Otherwise, sequence numbers are included on outgoing packets and checked
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on incoming packets.
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.Pp
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If
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.Va control_dseq
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is non-zero, then the setting of
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.Va enable_dseq
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will never change except by another
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.Dv NGM_L2TP_SET_SESS_CONFIG
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control message.
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If
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.Va control_dseq
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is zero, then the peer controls whether sequence numbers are used:
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if an incoming L2TP data packet contains sequence numbers,
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.Va enable_dseq
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is set to one, and conversely if an incoming L2TP data packet does not
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contain sequence numbers,
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.Va enable_dseq
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is set to zero.
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The current value of
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.Va enable_dseq
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is always accessible via the
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.Dv NGM_L2TP_GET_SESS_CONFIG
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control message (see below).
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Typically an LNS would set
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.Va control_dseq
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to one while a LAC would set
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.Va control_dseq
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to zero (if the Sequencing Required AVP were not sent), thus giving
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control of data packet sequencing to the LNS.
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.Pp
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The
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.Va include_length
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field determines whether the L2TP header length field is included
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in outgoing L2TP data packets.
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For incoming packets, the L2TP length field is always checked when present.
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.It Dv NGM_L2TP_GET_SESS_CONFIG
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This command takes a two byte session ID as an argument and returns
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the current configuration for the corresponding data session as a
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.Vt "struct ng_l2tp_sess_config" .
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The corresponding session hook must be connected.
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.It Dv NGM_L2TP_GET_STATS
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This command returns a
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.Vt "struct ng_l2tp_stats"
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containing statistics of the L2TP tunnel.
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.It Dv NGM_L2TP_CLR_STATS
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This command clears the statistics for the L2TP tunnel.
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.It Dv NGM_L2TP_GETCLR_STATS
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Same as
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.Dv NGM_L2TP_GET_STATS ,
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but also atomically clears the statistics as well.
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.It Dv NGM_L2TP_GET_SESSION_STATS
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This command takes a two byte session ID as an argument and returns a
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.Vt "struct ng_l2tp_session_stats"
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containing statistics for the corresponding data session.
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The corresponding session hook must be connected.
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.It Dv NGM_L2TP_CLR_SESSION_STATS
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This command takes a two byte session ID as an argument and
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clears the statistics for that data session.
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The corresponding session hook must be connected.
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.It Dv NGM_L2TP_GETCLR_SESSION_STATS
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Same as
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.Dv NGM_L2TP_GET_SESSION_STATS ,
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but also atomically clears the statistics as well.
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.It Dv NGM_L2TP_SET_SEQ
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This command sets the sequence numbers of a not yet enabled node.
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It takes a
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.Vt "struct ng_l2tp_seq_config"
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as argument, where
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.Va xack
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and
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.Va nr
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respectively
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.Va ns
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and
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.Va rack
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must be the same.
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This option is particularly useful if one receives and processes
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the first packet entirely in userspace and wants to hand over further
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processing to the node.
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.El
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.Sh SHUTDOWN
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This node shuts down upon receipt of a
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.Dv NGM_SHUTDOWN
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control message, or when all hooks have been disconnected.
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.Sh SEE ALSO
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.Xr netgraph 4 ,
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.Xr ng_ksocket 4 ,
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.Xr ng_ppp 4 ,
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.Xr ng_pptp 4 ,
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.Xr ngctl 8
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.Rs
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.%A W. Townsley
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.%A A. Valencia
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.%A A. Rubens
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.%A G. Pall
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.%A G. Zorn
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.%A B. Palter
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.%T "Layer Two Tunneling Protocol L2TP"
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.%O RFC 2661
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.Re
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.Sh HISTORY
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The
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.Nm l2tp
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node type was developed at Packet Design, LLC,
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.Pa http://www.packetdesign.com/ .
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.Sh AUTHORS
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.An Archie Cobbs Aq archie@packetdesign.com
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