Multicast Listener Discovery Protocol
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
and receive membership reports.
As of FreeBSD 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.
- This opaque read-only variable exposes the per-link MLDv2 status to
- 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.
- 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.
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