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IFMIB(4)	       FreeBSD Kernel Interfaces Manual		      IFMIB(4)

NAME
     ifmib -- Management Information Base for network interfaces

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>
     #include <sys/sysctl.h>
     #include <sys/time.h>
     #include <net/if.h>
     #include <net/if_mib.h>

DESCRIPTION
     The ifmib facility	is an application of the sysctl(3) interface to	pro-
     vide management information about network interfaces to client applica-
     tions such	as netstat(1), slstat(8), and SNMP management agents.  This
     information is structured as a table, where each row in the table repre-
     sents a logical network interface (either a hardware device or a software
     pseudo-device like	lo(4)).	 There are two columns in the table, each con-
     taining a single structure: one column contains generic information rele-
     vant to all interfaces, and the other contains information	specific to
     the particular class of interface.	 (Generally the	latter will implement
     the SNMP MIB defined for that particular interface	class, if one exists
     and can be	implemented in the kernel.)

     The ifmib facility	is accessed via	the ``net.link.generic'' branch	of the
     sysctl(3) MIB.  The manifest constants for	each level in the sysctl(3)
     name are defined in <net/if_mib.h>.  The index of the last	row in the ta-
     ble is given by ``net.link.generic.system.ifcount'' (or, using the	mani-
     fest constants, CTL_NET, PF_LINK, NETLINK_GENERIC,	IFMIB_SYSTEM,
     IFMIB_IFCOUNT).  A	management application searching for a particular
     interface should start with row 1 and continue through the	table row-by-
     row until the desired interface is	found, or the interface	count is
     reached.  Note that the table may be sparse, i.e.,	a given	row may	not
     exist, indicated by an errno of ENOENT.  Such an error should be ignored,
     and the next row should be	checked.

     The generic interface information,	common to all interfaces, can be
     accessed via the following	procedure:

	   int
	   get_ifmib_general(int row, struct ifmibdata *ifmd)
	   {
		   int name[6];
		   size_t len;

		   name[0] = CTL_NET;
		   name[1] = PF_LINK;
		   name[2] = NETLINK_GENERIC;
		   name[3] = IFMIB_IFDATA;
		   name[4] = row;
		   name[5] = IFDATA_GENERAL;

		   len = sizeof(*ifmd);

		   return sysctl(name, 6, ifmd,	&len, (void *)0, 0);
	   }

     The fields	in struct ifmibdata are	as follows:

     ifmd_name	     (char []) the name	of the interface, including the	unit
		     number

     ifmd_pcount     (int) the number of promiscuous listeners

     ifmd_flags	     (int) the interface's flags (defined in <net/if.h>)

     ifmd_snd_len    (int) the current instantaneous length of the send	queue

     ifmd_snd_drops  (int) the number of packets dropped at this interface
		     because the send queue was	full

     ifmd_data	     (struct if_data) more information from a structure
		     defined in	<net/if.h> (see	if_data(9))

     Class-specific information	can be retrieved by examining the
     IFDATA_LINKSPECIFIC column	instead.  Note that the	form and length	of the
     structure will depend on the class	of interface.  For IFT_ETHER,
     IFT_ISO88023, and IFT_STARLAN interfaces, the structure is	called
     ``struct ifmib_iso_8802_3'' (defined in <net/if_mib.h>), and implements a
     superset of the RFC 1650 MIB for Ethernet-like networks.

SEE ALSO
     sysctl(3),	intro(4), ifnet(9)

     F.	Kastenholz, Definitions	of Managed Objects for the Ethernet-like
     Interface Types Using SMIv2, August 1994, RFC 1650.

HISTORY
     The ifmib interface first appeared	in FreeBSD 2.2.

BUGS
     Many Ethernet-like	interfaces do not yet support the Ethernet MIB;	the
     interfaces	known to support it include ed(4) and de(4).  Regardless, all
     interfaces	automatically support the generic MIB.

FreeBSD	10.1		       October 28, 2009			  FreeBSD 10.1

NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | BUGS

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