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NG_PPP(4)                BSD Kernel Interfaces Manual                NG_PPP(4)

     ng_ppp -- PPP protocol netgraph node type

     #include <&lt;netgraph/ng_ppp.h>&gt;

     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).

     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.  When
     enabled and connected, the PPP node writes outgoing frames on the comp
     hook and expects to receive back the compressed frame on the same hook.
     Similarly, the decompress hook is used to uncompress incoming frames when
     decompression is negotiated (compression and decompression are indepen-
     dently negotiable).  The type of node attached to these hooks should cor-
     respond to the type of compression negotiated, e.g., Deflate, Predic-
     tor-1, etc.

     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.

     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's not
     ready for the protocol) or with an LCP protocol reject (if it doesn't
     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.

     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.

          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.

     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).

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

     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.

     The ng_ppp node type was implemented in FreeBSD 4.0.

     Archie Cobbs <archieATFreeBSD.org>

BSD                             August 2, 2004                             BSD