.\"	$KAME: ifmcstat.8,v 1.6 2002/10/31 04:23:43 suz Exp $
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.\" Copyright (c) 2007-2009 Bruce Simpson.
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.\" $FreeBSD$
.\"
.Dd May 27, 2009
.Dt IFMCSTAT 8
.Os
.Sh NAME
.Nm ifmcstat
.Nd dump multicast group management statistics per interface
.Sh SYNOPSIS
.Nm
.Op Fl i Ar interface
.Op Fl f Ar address-family
.Op Fl v
.Op Fl K
.Op Fl M Ar core
.Op Fl N Ar system
.\"
.Sh DESCRIPTION
The
.Nm
command dumps multicast group information from the kernel.
.Pp
The following options are supported:
.Bl -tag -width Fl
.It Fl i Ar interface
specifies the interface to be displayed.
.Pp
.It Fl f Ar address-family
specifies the address family to be displayed;
.Ar inet ,
.Ar inet6
and
.Ar link
are supported.
.It Fl v
specifies that link-layer memberships should be printed;
they are suppressed by default.
It may not be specified for
.Fl f Ar link .
Source lists for each group will also be printed.
.Pp
If specified twice, and
.Xr kvm 3
is in use, the control plane timers for each interface
and the source list counters for each group
will also be printed.
.El
.Pp
The following options are only available if
.Nm
has been built with support for
.Xr kvm 3 :
.Bl -tag -width Fl
.It Fl K
attempts to use
.Xr kvm 3
to retrieve the multicast group information.
.It Fl M Ar core
extracts values associated with the name list from the specified core,
instead of the default
.Pa /dev/kmem .
.It Fl N Ar system
extracts the name list from the specified kernel instead of the
default, which is the kernel image the system has booted from.
.El
.Sh IMPLEMENTATION NOTES
.Nm
will always print the embedded scope IDs of IPv6 multicast group
memberships.
This is because memberships are always scoped to an interface.
.Pp
When run with the
.Fl v
option,
.Nm
may print multicast MAC addresses twice if they are
referenced by a layer 3 protocol.
.Pp
When run with
.Xr kvm 3
support,
the names of all interfaces configured in the system will be
printed in the first column of output, even if no multicast
group memberships are present on those interfaces.
The output may also be slightly different, as the kernel
data structures are being traversed with minimal post-processing
of the output.
.Pp
When built without
.Xr kvm 3
support, the information displayed by
.Nm
is more limited.
This support is recommended for debugging purposes.
It requires super-user privilege if used to inspect a running kernel.
.Sh SEE ALSO
.Xr netstat 1 ,
.Xr getifaddrs 3 ,
.Xr getifmaddrs 3 ,
.Xr kvm 3