xref: /freebsd/share/man/man4/ifmib.4 (revision fa9896e082a1046ff4fbc75fcba4d18d1f2efc19)

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.Dd December 26, 2020
.Dt IFMIB 4
.Os
.Sh NAME
.Nm ifmib
.Nd Management Information Base for network interfaces
.Sh SYNOPSIS
.In sys/types.h
.In sys/socket.h
.In sys/sysctl.h
.In sys/time.h
.In net/if.h
.In net/if_mib.h
.Sh DESCRIPTION
The
.Nm
facility is an application of the
.Xr sysctl 3
interface to provide management information about network interfaces
to client applications such as
.Xr netstat 1 ,
.Xr slstat 8 ,
and
.Tn SNMP
management agents.
This information is structured as a table, where
each row in the table represents a logical network interface (either a
hardware device or a software pseudo-device like
.Xr lo 4 ) .
There are two columns in the table, each containing a single
structure: one column contains generic information relevant to all
interfaces, and the other contains information specific to the
particular class of interface.
(Generally the latter will implement
the
.Tn SNMP
.Tn MIB
defined for that particular interface class, if one exists and can be
implemented in the kernel.)
.Pp
The
.Nm
facility is accessed via the
.Dq Li net.link.generic
branch of the
.Xr sysctl 3
MIB.
The manifest constants for each level in the
.Xr sysctl 3
.Ar name
are defined in
.In net/if_mib.h .
The index of the last row in the table is given by
.Dq Li net.link.generic.system.ifcount
(or, using the manifest constants,
.Dv CTL_NET ,
.Dv PF_LINK ,
.Dv NETLINK_GENERIC ,
.Dv IFMIB_SYSTEM ,
.Dv 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
.Va errno
of
.Er ENOENT .
Such an error should be ignored, and the next row should be checked.
.Pp
The generic interface information, common to all interfaces,
can be accessed via the following procedure:
.Bd -literal -offset indent
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);
}
.Ed
.Pp
The fields in
.Li struct ifmibdata
are as follows:
.Bl -tag -width "ifmd_snd_drops"
.It Li ifmd_name
.Pq Li "char []"
the name of the interface, including the unit number
.It Li ifmd_pcount
.Pq Li int
the number of promiscuous listeners
.It Li ifmd_flags
.Pq Li int
the interface's flags (defined in
.In net/if.h )
.It Li ifmd_snd_len
.Pq Li int
the current instantaneous length of the send queue
.It Li ifmd_snd_drops
.Pq Li int
the number of packets dropped at this interface because the send queue
was full
.It Li ifmd_data
.Pq Li struct if_data
more information from a structure defined in
.In net/if.h
(see
.Xr if_data 9 )
.El
.Pp
Class-specific information can be retrieved by examining the
.Dv IFDATA_LINKSPECIFIC
column instead.
Note that the form and length of the structure will
depend on the class of interface.
For
.Dv IFT_ETHER ,
.Dv IFT_ISO88023 ,
and
.Dv IFT_STARLAN
interfaces, the structure is called
.Dq Li struct ifmib_iso_8802_3
(defined in
.In net/if_mib.h ) ,
and implements a superset of the
.Tn "RFC 1650"
MIB for Ethernet-like networks.
.Sh SEE ALSO
.Xr sysctl 3 ,
.Xr intro 4 ,
.Xr ifnet 9
.\" .Xr ethermib 4 ,
.Rs
.%T "Definitions of Managed Objects for the Ethernet-like Interface Types Using SMIv2"
.%A F. Kastenholz
.%D August 1994
.%O RFC 1650
.Re
.Sh HISTORY
The
.Nm
interface first appeared in
.Fx 2.2 .
.Sh BUGS
Many Ethernet-like interfaces do not yet support the Ethernet MIB.
Regardless, all interfaces automatically support the generic MIB.