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NG_PPP(4) FreeBSD Kernel Interfaces Manual NG_PPP(4)


[править] NAME

    ng_ppp -- PPP protocol netgraph node type

[править] SYNOPSIS

    #include <sys/types.h>
    #include <netgraph/ng_ppp.h>


    The ppp node type performs multiplexing for the PPP protocol.  It handles
    only packets that contain data, and forwards protocol negotiation and
    control packets to a separate controlling entity (e.g., a user-land dae-
    mon).  This approach combines the fast dispatch of kernel implementations
    with the configuration flexibility of a user-land implementations.  The
    PPP node type directly supports multi-link PPP, Van Jacobson compression,
    PPP compression, PPP encryption, and the IP, IPX, and AppleTalk proto-
    cols.  A single PPP node corresponds to one PPP multi-link bundle.
    There is a separate hook for each PPP link in the bundle, plus several
    hooks corresponding to the directly supported protocols.  For compression
    and encryption, separate attached nodes are required to do the actual
    work.  The node type used will of course depend on the algorithm negoti-
    ated.  There is also a bypass hook which is used to handle any protocol
    not directly supported by the node.  This includes all of the control
    protocols: LCP, IPCP, CCP, etc.  Typically this node is connected to a
    user-land daemon via a ng_socket(4) type node.


    In general, the PPP node enables a specific link or functionality when
    (a) a NGM_PPP_SET_CONFIG message has been received which enables it, and
    (b) the corresponding hook(s) are connected.  This allows the controlling
    entity to use either method (a) or (b) (or both) to control the node's
    behavior.  When a link is connected but disabled, traffic can still flow
    on the link via the bypass hook (see below).

[править] LINK HOOKS

    During normal operation, the individual PPP links are connected to hooks
    link0, link1, etc.  Up to NG_PPP_MAX_LINKS links are supported.  These
    device-independent hooks transmit and receive full PPP frames, which
    include the PPP protocol, address, control, and information fields, but
    no checksum or other link-specific fields.
    On outgoing frames, when protocol compression has been enabled and the
    protocol number is suitable for compression, the protocol field will be
    compressed (i.e., sent as one byte instead of two).  Either compressed or
    uncompressed protocol fields are accepted on incoming frames.  Similarly,
    if address and control field compression has been enabled for the link,
    the address and control fields will be omitted (except for LCP frames as
    required by the standards).  Incoming frames have the address and control
    fields stripped automatically if present.
    Since all negotiation is handled outside the PPP node, the links should
    not be connected and enabled until the corresponding link has reached the
    network phase (i.e., LCP negotiation and authentication have completed
    successfully) and the PPP node has been informed of the link parameters
    via the NGM_PPP_LINK_CONFIG message.
    When a link is connected but disabled, all received frames are forwarded
    directly out the bypass hook, and conversely, frames may be transmitted
    via the bypass hook as well.  This mode is appropriate for the link
    authentication phase.  As soon as the link is enabled, the PPP node will
    begin processing frames received on the link.


    Compression is supported via two hooks, compress and decompress.  Com-
    pression and decompression can be enabled by toggling the
    enableCompression and enableDecompression fields of the node configura-
    tion structure.  (See below.)  If enableCompression is set to
    NG_PPP_COMPRESS_SIMPLE, then all outgoing frames are sent to the compress
    hook and all packets received on this hook are expected to be compressed,
    so the COMPD tag is put on them unconditionally.  If enableCompression is
    set to NG_PPP_COMPRESS_FULL, then packets received on the compress hook
    are resent as is.  The compressor node should put the tag, if the packet
    was compressed.  If enableDecompression is set to
    NG_PPP_DECOMPRESS_SIMPLE, then the node will sent to the decompress hook
    only those frames, that are marked with the COMPD tag.  If
    enableDecompression is set to NG_PPP_DECOMPRESS_FULL, then the node will
    sent all incoming packets to the decompress hook.  Compression and decom-
    pression can be completely disabled by setting the enableCompression and
    enableDecompression fields to the NG_PPP_COMPRESS_NONE and
    NG_PPP_DECOMPRESS_NONE, respectively.
    Encryption works exactly analogously via the encrypt and decrypt nodes.
    Data is always compressed before being encrypted, and decrypted before
    being decompressed.
    Only bundle-level compression and encryption is directly supported; link-
    level compression and encryption can be handled transparently by down-
    stream nodes.


    When all of the vjc_ip, vjc_vjcomp, vjc_vjuncomp, and vjc_vjip hooks are
    connected, and the corresponding configuration flag is enabled, Van
    Jacobson compression and/or decompression will become active.  Normally
    these hooks connect to the corresponding hooks of a single ng_vjc(4)
    node.  The PPP node is compatible with the ``pass through modes of the
    ng_vjc(4) node type.

[править] BYPASS HOOK

    When a frame is received on a link with an unsupported protocol, or a
    protocol which is disabled or for which the corresponding hook is uncon-
    nected, the PPP node forwards the frame out the bypass hook, prepended
    with a four byte prefix.  This first two bytes of the prefix indicate the
    link number on which the frame was received (in network order).  For such
    frames received over the bundle (i.e., encapsulated in the multi-link
    protocol), the special link number NG_PPP_BUNDLE_LINKNUM is used.  After
    the two byte link number is the two byte PPP protocol number (also in
    network order).  The PPP protocol number is two bytes long even if the
    original frame was protocol compressed.
    Conversely, any data written to the bypass hook is assumed to be in this
    same format.  The four byte header is stripped off, the PPP protocol num-
    ber is prepended (possibly compressed), and the frame is delivered over
    the desired link.  If the link number is NG_PPP_BUNDLE_LINKNUM the frame
    will be delivered over the multi-link bundle; or, if multi-link is dis-
    abled, over the (single) PPP link.
    Typically when the controlling entity receives an unexpected packet on
    the bypass hook it responds either by dropping the frame (if it is not
    ready for the protocol) or with an LCP protocol reject (if it does not
    recognize or expect the protocol).


    To enable multi-link PPP, the corresponding configuration flag must be
    set and at least one link connected.  The PPP node will not allow more
    than one link to be connected if multi-link is not enabled, nor will it
    allow certain multi-link settings to be changed while multi-link opera-
    tion is active (e.g., short sequence number header format).
    Since packets are sent as fragments across multiple individual links, it
    is important that when a link goes down the PPP node is notified immedi-
    ately, either by disconnecting the corresponding hook or disabling the
    link via the NGM_PPP_SET_CONFIG control message.
    Each link has configuration parameters for latency (specified in mil-
    liseconds) and bandwidth (specified in tens of bytes per second).  The
    PPP node can be configured for round-robin or optimized packet delivery.
    When configured for round-robin delivery, the latency and bandwidth val-
    ues are ignored and the PPP node simply sends each frame as a single
    fragment, alternating frames across all the links in the bundle.  This
    scheme has the advantage that even if one link fails silently, some pack-
    ets will still get through.  It has the disadvantage of sub-optimal over-
    all bundle latency, which is important for interactive response time, and
    sub-optimal overall bundle bandwidth when links with different bandwidths
    exist in the same bundle.
    When configured for optimal delivery, the PPP node distributes the packet
    across the links in a way that minimizes the time it takes for the com-
    pleted packet to be received by the far end.  This involves taking into
    account each link's latency, bandwidth, and current queue length.  There-
    fore these numbers should be configured as accurately as possible.  The
    algorithm does require some computation, so may not be appropriate for
    very slow machines and/or very fast links.
    As a special case, if all links have identical latency and bandwidth,
    then the above algorithm is disabled (because it is unnecessary) and the
    PPP node simply fragments frames into equal sized portions across all of
    the links.

[править] HOOKS

    This node type supports the following hooks:
    link<N>       Individual PPP link number <N>
    compress      Connection to compression engine
    decompress    Connection to decompression engine
    encrypt       Connection to encryption engine
    decrypt       Connection to decryption engine
    vjc_ip        Connection to ng_vjc(4) ip hook
    vjc_vjcomp    Connection to ng_vjc(4) vjcomp hook
    vjc_vjuncomp  Connection to ng_vjc(4) vjuncomp hook
    vjc_vjip      Connection to ng_vjc(4) vjip hook
    inet          IP packet data
    atalk         AppleTalk packet data
    ipx           IPX packet data
    bypass        Bypass hook; frames have a four byte header consisting of a
                  link number and a PPP protocol number.


    This node type supports the generic control messages, plus the following:
         This command configures all aspects of the node.  This includes
         enabling multi-link PPP, encryption, compression, Van Jacobson com-
         pression, and IP, IPv6, AppleTalk, and IPX packet delivery.  It
         includes per-link configuration, including enabling the link, set-
         ting latency and bandwidth parameters, and enabling protocol field
         compression.  Note that no link or functionality is active until the
         corresponding hook is also connected.  This command takes a struct
         ng_ppp_node_conf as an argument:
         /* Per-link config structure */
         struct ng_ppp_link_conf {
           u_char    enableLink;     /* enable this link */
           u_char    enableProtoComp;/* enable protocol field compression */
           u_char    enableACFComp;  /* enable addr/ctrl field compression */
           u_int16_t mru;            /* peer MRU */
           u_int32_t latency;        /* link latency (in milliseconds) */
           u_int32_t bandwidth;      /* link bandwidth (in bytes/second) */
         /* Bundle config structure */
         struct ng_ppp_bund_conf {
           u_int16_t mrru;                   /* multilink peer MRRU */
           u_char    enableMultilink;        /* enable multilink */
           u_char    recvShortSeq;           /* recv multilink short seq # */
           u_char    xmitShortSeq;           /* xmit multilink short seq # */
           u_char    enableRoundRobin;       /* xmit whole packets */
           u_char    enableIP;               /* enable IP data flow */
           u_char    enableIPv6;             /* enable IPv6 data flow */
           u_char    enableAtalk;            /* enable AppleTalk data flow */
           u_char    enableIPX;              /* enable IPX data flow */
           u_char    enableCompression;      /* enable PPP compression */
           u_char    enableDecompression;    /* enable PPP decompression */
           u_char    enableEncryption;       /* enable PPP encryption */
           u_char    enableDecryption;       /* enable PPP decryption */
           u_char    enableVJCompression;    /* enable VJ compression */
           u_char    enableVJDecompression;  /* enable VJ decompression */
         struct ng_ppp_node_conf {
           struct ng_ppp_bund_conf   bund;
           struct ng_ppp_link_conf   links[NG_PPP_MAX_LINKS];
         Returns the current configuration as a struct ng_ppp_node_conf.
         This command takes a two byte link number as an argument and returns
         a struct ng_ppp_link_stat containing statistics for the correspond-
         ing link.  Here NG_PPP_BUNDLE_LINKNUM is a valid link number corre-
         sponding to the multi-link bundle.
         Same as NGM_PPP_GET_LINK_STATS but returns struct ng_ppp_link_stat64
         containing 64bit counters.
         This command takes a two byte link number as an argument and clears
         the statistics for that link.
         Same as NGM_PPP_GET_LINK_STATS, but also atomically clears the sta-
         tistics as well.
         Same as NGM_PPP_GETCLR_LINK_STATS but returns struct
         ng_ppp_link_stat64 containing 64bit counters.
    This node type also accepts the control messages accepted by the
    ng_vjc(4) node type.  When received, these messages are simply forwarded
    to the adjacent ng_vjc(4) node, if any.  This is particularly useful when
    the individual PPP links are able to generate NGM_VJC_RECV_ERROR messages
    (see ng_vjc(4) for a description).

[править] SHUTDOWN

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

[править] SEE ALSO

netgraph(4) • ng_async(4) • ng_iface(4) • ng_mppc(4) • ng_pppoe(4) • ng_vjc(4) • ngctl(8)

    W. Simpson, The Point-to-Point Protocol (PPP), RFC 1661.
    K. Sklower, B. Lloyd, G. McGregor, D. Carr, and T. Coradetti, The PPP
    Multilink Protocol (MP), RFC 1990.

[править] HISTORY

    The ng_ppp node type was implemented in FreeBSD 4.0.

[править] AUTHORS

    Archie Cobbs <>

FreeBSD 9.0 December 28, 2006 FreeBSD 9.0


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