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.\" $FreeBSD: release/9.1.0/share/man/man4/mld.4 213573 2010-10-08 12:40:16Z uqs $
.\"
.Dd May 27, 2009
.Dt MLD 4
.Os
.Sh NAME
.Nm mld
.Nd Multicast Listener Discovery Protocol
.Sh SYNOPSIS
.In sys/types.h
.In sys/socket.h
.In netinet/in.h
.In netinet/in_systm.h
.In netinet/ip6.h
.In netinet/icmp6.h
.In netinet6/mld6.h
.Ft int
.Fn socket AF_INET6 SOCK_RAW IPPROTO_ICMPV6
.Sh DESCRIPTION
.Tn MLD
is a control plane protocol used by IPv6 hosts and routers to
propagate multicast group membership information.
Normally this protocol is not used directly, except by the kernel
itself, in response to multicast membership requests by user
applications.
Multicast routing protocol daemons may open a raw socket to directly
interact with
.Nm 
and receive membership reports.
.Pp
As of
.Fx 8.0 ,
MLD version 2 is implemented.
This adds support for Source-Specific Multicast (SSM), whereby
applications may communicate to upstream multicast routers that
they are only interested in receiving multicast streams from
particular sources.
The retransmission of state-change reports adds some robustness
to the protocol.
.\"
.Sh SYSCTL VARIABLES
.Bl -tag -width indent
.\"
.It net.inet6.mld.stats
This opaque read-only variable exposes the stack-wide MLDv2
protocol statistics to
.Xr netstat 1 .
.\"
.It net.inet6.mld.ifinfo
This opaque read-only variable exposes the per-link MLDv2 status to
.Xr ifmcstat 8 .
.\"
.It net.inet6.mld.gsrdelay
This variable specifies the time threshold, in seconds, for processing
Group-and-Source Specific Queries (GSR).
As GSR query processing requires maintaining state on the host,
it may cause memory to be allocated, and is therefore a potential
attack point for Denial-of-Service (DoS).
If more than one GSR query is received within this threshold,
it will be dropped, to mitigate the potential for DoS.
.\"
.It net.inet6.mld.v1enable
If this variable is non-zero, then MLDv1 membership queries (and host
reports) will be processed by this host, and backwards compatibility
will be enabled until the v1 'Older Version Querier Present' timer expires.
This sysctl is normally enabled by default.
.\"
.El
.Sh SEE ALSO
.Xr ifmcstat 8 ,
.Xr inet 4 ,
.Xr multicast 4 ,
.Xr netstat 1 ,
.Xr sourcefilter 3
.Sh HISTORY
The
.Nm
manual page appeared in
.Fx 8.0 .