MLD(4)

💅 MLD(4) — Multicast Listener Discovery Protocol 💅

okay so bestie, this is the Kernel Interfaces Manual page for MLD(4), and it’s lowkey iconic in the IPv6 multicast world. Let’s get into it 💖

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✨ NAME ✨

mld — Multicast Listener Discovery Protocol

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🌸 SYNOPSIS 🌸

Include these exact headers and open the socket like this, bestie:

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip6.h>
#include <netinet/icmp6.h>
#include <netinet6/mld6.h>

int
socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);

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🦋 DESCRIPTION 🦋

The way MLD works: it’s a control plane protocol that IPv6 hosts and routers use 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 mld and receive membership reports. slay.

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. periodt 💅

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🎀 SYSCTL VARIABLES 🎀

• net.inet6.mld.ifinfo — This opaque read-only variable exposes the per-link MLDv2 status to ifmcstat(8).
• net.inet6.mld.gsrdelay — This variable specifies the time threshold, in seconds, for processing Group-and-Source Specific Queries (GSR). GSR query processing requires maintaining state on the host, so 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. no cap, that’s the safety vibe 🫶
• 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. cute backwards-compat behavior fr fr 💖

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🌈 SEE ALSO 🌈

netstat(1), sourcefilter(3), icmp6(4), inet(4), multicast(4), ifmcstat(8)

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👑 HISTORY 👑

The mld manual page appeared in FreeBSD 8.0.

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Debian source/version • April 8, 2013 • MLD(4) — bye bestie, mwah 💋