This node type supports the generic control messages, plus the following:
NGM_L2TP_SET_CONFIG (setconfig)
This command updates the configuration of the node. It takes a structng_l2tp_config as an
argument:
/* 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 */
};
The 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.
The tunnel_id field configures the local tunnel ID for the control connection. The match_id field
determines how incoming L2TP packets with a tunnel ID field different from tunnel_id are handled.
If match_id is non-zero, they will be dropped; otherwise, they will be dropped only if the tunnel ID
is non-zero. Typically tunnel_id is set to the local tunnel ID as soon as it is known and match_id
is set to non-zero after receipt of the SCCRP or SCCCN control message.
The peer's tunnel ID should be set in 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.
The peer_win field should be set from the “Receive Window Size” AVP received from the peer. The
default value for this field is one; zero is an invalid value. As long as enabled is non-zero, this
value may not be decreased.
The rexmit_max and rexmit_max_to fields configure packet retransmission. 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 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 l2tp
node to send a NGM_L2TP_ACK_FAILURE (ackfailure) control message back to the node that sent the last
NGM_L2TP_SET_CONFIG. Appropriate action should then be taken to shutdown the control connection.
NGM_L2TP_GET_CONFIG (getconfig)
Returns the current configuration as a structng_l2tp_config.
NGM_L2TP_SET_SESS_CONFIG (setsessconfig)
This control message configures a single data session. The corresponding hook must already be
connected before sending this command. The argument is a structng_l2tp_sess_config:
/* 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 */
};
The session_id and peer_id fields configure the local and remote session IDs, respectively.
The control_dseq and enable_dseq fields determine whether sequence numbers are used with L2TP data
packets. If 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.
If control_dseq is non-zero, then the setting of enable_dseq will never change except by another
NGM_L2TP_SET_SESS_CONFIG control message. If control_dseq is zero, then the peer controls whether
sequence numbers are used: if an incoming L2TP data packet contains sequence numbers, enable_dseq is
set to one, and conversely if an incoming L2TP data packet does not contain sequence numbers,
enable_dseq is set to zero. The current value of enable_dseq is always accessible via the
NGM_L2TP_GET_SESS_CONFIG control message (see below). Typically an LNS would set control_dseq to
one while a LAC would set control_dseq to zero (if the Sequencing Required AVP were not sent), thus
giving control of data packet sequencing to the LNS.
The 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.
NGM_L2TP_GET_SESS_CONFIG (getsessconfig)
This command takes a two byte session ID as an argument and returns the current configuration for
the corresponding data session as a structng_l2tp_sess_config. The corresponding session hook must
be connected.
NGM_L2TP_GET_STATS (getstats)
This command returns a structng_l2tp_stats containing statistics of the L2TP tunnel.
NGM_L2TP_CLR_STATS (clrstats)
This command clears the statistics for the L2TP tunnel.
NGM_L2TP_GETCLR_STATS (getclrstats)
Same as NGM_L2TP_GET_STATS, but also atomically clears the statistics as well.
NGM_L2TP_GET_SESSION_STATS (getsessstats)
This command takes a two byte session ID as an argument and returns a structng_l2tp_session_stats
containing statistics for the corresponding data session. The corresponding session hook must be
connected.
NGM_L2TP_CLR_SESSION_STATS (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.
NGM_L2TP_GETCLR_SESSION_STATS (getclrsessstats)
Same as NGM_L2TP_GET_SESSION_STATS, but also atomically clears the statistics as well.
NGM_L2TP_SET_SEQ (setsequence)
This command sets the sequence numbers of a not yet enabled node. It takes a structng_l2tp_seq_config as argument, where xack and nr respectively ns and 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.
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