Manual Pages  — NG_L2TP

• SYNOPSIS
• DESCRIPTION
• HOOKS
• CONTROL MESSAGES
• SHUTDOWN
• SEE ALSO
• HISTORY
• AUTHORS

/* 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.

/* 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.