ng_deflate(4) Deflate PPP compression (RFC 1979) netgraph node type


In sys/types.h In netgraph/ng_deflate.h


The deflate node type implements the Deflate sub-protocols of the Compression Control Protocol (CCP).

The node has two hooks, comp for compression and decomp for decompression. Only one of them can be connected at the same time, specifying node's operation mode. Typically that hooks would be connected to the ng_ppp4 node type hook of the same name. Corresponding ng_ppp4 node hook must be switched to NG_PPP_DECOMPRESS_FULL mode to permit sending uncompressed frames.


This node type supports the following hooks:

Connection to ng_ppp4 comp hook. Incoming frames are compressed (if possible) and sent back out the same hook.
Connection to ng_ppp4 decomp hook. Incoming frames are decompressed (if they are compressed), and sent back out the same hook.

Only one hook can be connected at the same time, specifying node's operation mode.


This node type supports the generic control messages, plus the following:

This command resets and configures the node for a session (i.e., for compression or decompression). This command takes a Vt struct ng_deflate_config as an argument:
struct ng_deflate_config {
        u_char  enable;                 /* node enabled */
        u_char  windowBits;             /* log2(Window size) */
The Fa enabled field enables traffic flow through the node. The Fa windowBits specify compression windows size as negotiated by the Compression Control Protocol (CCP) in PPP.
This message contains no arguments, and is bi-directional. If an error is detected during decompression, this message is sent by the node to the originator of the NGM_DEFLATE_CONFIG message that initiated the session. The receiver should respond by sending a PPP CCP Reset-Request to the peer.

This message may also be received by this node type when a CCP Reset-Request or Reset-Ack is received by the local PPP entity. The node will respond by flushing its compression state so the sides can resynchronize.

This control message obtains statistics for a given hook. The statistics are returned in Vt struct ng_deflate_stats :
struct ng_deflate_stats {
        uint64_t        FramesPlain;
        uint64_t        FramesComp;
        uint64_t        FramesUncomp;
        uint64_t        InOctets;
        uint64_t        OutOctets;
        uint64_t        Errors;
This control message clears statistics for a given hook.
This control message obtains and clears statistics for a given hook.


This node shuts down upon receipt of a NGM_SHUTDOWN control message, or when hook have been disconnected.


An Alexander Motin Aq [email protected]


Due to nature of netgraph PPP implementation there are possible race conditions between data packet and ResetAck CCP packet in case of packet loss. As result, packet loss can produce bigger performance degradation than supposed by protocol.