ng_tcpmss(4) [freebsd man page]

NG_TCPMSS(4)						   BSD Kernel Interfaces Manual 					      NG_TCPMSS(4)

NAME

     ng_tcpmss -- netgraph node to adjust TCP MSS option

SYNOPSIS

     #include <netgraph.h>
     #include <netgraph/ng_tcpmss.h>

DESCRIPTION

     The tcpmss node type is designed to alter the Maximum Segment Size option of TCP packets.	This node accepts an arbitrary number of hooks.
     Initially a new hook is considered unconfigured.  The NG_TCPMSS_CONFIG control message is used to configure a hook.

CONTROL MESSAGES

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

     NGM_TCPMSS_CONFIG (config)
	  This control message configures node to do given MSS adjusting on a particular hook.	It requires the struct ng_tcpmss_config to be sup-
	  plied as an argument:

	  struct ng_tcpmss_config {
		  char		  inHook[NG_HOOKSIZ];
		  char		  outHook[NG_HOOKSIZ];
		  uint16_t	  maxMSS;
	  }

	  This means: packets received on inHook would be checked for TCP MSS option and the latter would be reduced down to maxMSS if it exceeds
	  maxMSS.  After that, packets would be sent to hook outHook.

     NGM_TCPMSS_GET_STATS (getstats)
	  This control message obtains statistics for a given hook.  The statistics are returned in struct ng_tcpmss_hookstat:

	  struct ng_tcpmss_hookstat {
		  uint64_t	  Octets;	  /* total bytes */
		  uint64_t	  Packets;	  /* total packets */
		  uint16_t	  maxMSS;	  /* maximum MSS */
		  uint64_t	  SYNPkts;	  /* TCP SYN packets */
		  uint64_t	  FixedPkts;	  /* changed packets */
	  };

     NGM_TCPMSS_CLR_STATS (clrstats)
	  This control message clears statistics for a given hook.

     NGM_TCPMSS_GETCLR_STATS (getclrstats)
	  This control message obtains and clears statistics for a given hook.

EXAMPLES

     In the following example, packets are injected into the tcpmss node using the ng_ipfw(4) node.

	   # Create tcpmss node and connect it to ng_ipfw node
	   ngctl mkpeer ipfw: tcpmss 100 qqq

	   # Adjust MSS to 1452
	   ngctl msg ipfw:100 config '{ inHook="qqq" outHook="qqq" maxMSS=1452 }'

	   # Divert traffic into tcpmss node
	   ipfw add 300 netgraph 100 tcp from any to any tcpflags syn out via fxp0

	   # Let packets continue with ipfw after being hacked
	   sysctl net.inet.ip.fw.one_pass=0

SHUTDOWN

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

SEE ALSO

     netgraph(4), ng_ipfw(4)

HISTORY

     The ng_tcpmss node type was implemented in FreeBSD 6.0.

AUTHORS

     Alexey Popov <lollypop@flexuser.ru>
     Gleb Smirnoff <glebius@FreeBSD.org>

BUGS

     When running on SMP, system statistics may be broken.

BSD
								   June 9, 2005 							       BSD

NG_PRED1(4)						   BSD Kernel Interfaces Manual 					       NG_PRED1(4)

NAME

     ng_pred1 -- Predictor-1 PPP compression (RFC 1978) netgraph node type

SYNOPSIS

     #include <sys/types.h>
     #include <netgraph/ng_pred1.h>

DESCRIPTION

     The pred1 node type implements the Predictor-1 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_ppp(4) node type hook of the same name.

HOOKS

     This node type supports the following hooks:

     comp    Connection to ng_ppp(4) compress hook.  Incoming frames are compressed and sent back out the same hook.
     decomp  Connection to ng_ppp(4) decompress hook.  Incoming frames are decompressed and sent back out the same hook.

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

CONTROL MESSAGES

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

     NGM_PRED1_CONFIG (config)
	  This command resets and configures the node for a session (i.e., for compression or decompression).  This command takes a struct
	  ng_pred1_config as an argument:

	  struct ng_pred1_config {
		  u_char	  enable;		  /* node enabled */
	  };
	  The enable field enables traffic flow through the node.

     NGM_PRED1_RESETREQ (resetreq)
	  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_PRED1_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.

     NGM_PRED1_GET_STATS (getstats)
	  This control message obtains statistics for a given hook.  The statistics are returned in struct ng_pred1_stats:

	  struct ng_pred1_stats {
		  uint64_t	  FramesPlain;
		  uint64_t	  FramesComp;
		  uint64_t	  FramesUncomp;
		  uint64_t	  InOctets;
		  uint64_t	  OutOctets;
		  uint64_t	  Errors;
	  };

     NGM_PRED1_CLR_STATS (clrstats)
	  This control message clears statistics for a given hook.

     NGM_PRED1_GETCLR_STATS (getclrstats)
	  This control message obtains and clears statistics for a given hook.

SHUTDOWN

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

SEE ALSO

     netgraph(4), ng_ppp(4), ngctl(8)

     D. Rand, PPP Predictor Compression Protocol, RFC 1978.

     W. Simpson, The Point-to-Point Protocol (PPP), RFC 1661.

AUTHORS

     Alexander Motin <mav@alkar.net>

BUGS

     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.

BSD
								 December 24, 2006							       BSD