Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
NG_TCPMSS(4)		     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  mes-
     sage 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 statis-
	  tics 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.

FreeBSD ports 15.quarterly	  June 9, 2005			    NG_TCPMSS(4)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=ng_tcpmss&sektion=4&manpath=FreeBSD+15.1-RELEASE+and+Ports.quarterly>

home | help