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IFMIB(4)		 BSD Kernel Interfaces Manual		      IFMIB(4)

     ifmib -- Management Information Base for network interfaces

     #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>

     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 "" 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 "" (or, using the manifest
     IFMIB_IFCOUNT).  A	management application searching for a particular in-
     terface 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, indi-
     cated 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 ac-
     cessed via	the following procedure:

	   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

     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 be-
		     cause the send queue was full

     ifmd_data	     (struct if_data) more information from a structure	de-
		     fined 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.

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

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

     The ifmib interface first appeared	in FreeBSD 2.2.

     Many Ethernet-like	interfaces do not yet support the Ethernet MIB.	 Re-
     gardless, all interfaces automatically support the	generic	MIB.

BSD			       December	26, 2020			   BSD


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