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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);
	   }


     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.  For IFT_SLIP,
     the structure is a ``struct sl_softc'' (<net/if_slvar.h>).

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.

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.

HISTORY

     The ifmib interface first appeared in FreeBSD 2.2.

FreeBSD 5.4		       November 15, 1996		   FreeBSD 5.4

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