Provided by: freebsd-manpages_11.1-3_all 
NAME
igmp — Internet Group Management Protocol
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/igmp.h>
int
socket(AF_INET, SOCK_RAW, IPPROTO_IGMP);
DESCRIPTION
IGMP is a control plane protocol used by IPv4 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. Routing protocols may open a raw socket to directly
interact with igmp.
As of FreeBSD 8.0, IGMP version 3 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.
SYSCTL VARIABLES
net.inet.igmp.stats
This opaque read-only variable exposes the stack-wide IGMPv3 protocol statistics to netstat(1).
net.inet.igmp.ifinfo
This opaque read-only variable exposes the per-link IGMPv3 status to ifmcstat(8).
net.inet.igmp.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.
net.inet.igmp.default_version
This variable controls the default version of IGMP to be used on all links. This sysctl is
normally set to 3 by default.
net.inet.igmp.legacysupp
If this variable is non-zero, then IGMP v1 and v2 membership reports received on a link will be
allowed to suppress the IGMP v3 state-change reports which would otherwise be issued by this host.
This sysctl is normally enabled by default.
net.inet.igmp.v2enable
If this variable is non-zero, then IGMP v2 membership queries will be processed by this host, and
backwards compatibility will be enabled until the v2 'Old Querier Present' timer expires. This
sysctl is normally enabled by default.
net.inet.igmp.v1enable
If this variable is non-zero, then IGMP v1 membership queries will be processed by this host, and
backwards compatibility will be enabled until the v1 'Old Querier Present' timer expires. This
sysctl is normally enabled by default.
net.inet.igmp.sendlocal
If this variable is non-zero, then IGMP state-changes for groups in the 224.0.0.0/24 link-scope
prefix will be issued. This behaviour is recommended if deploying FreeBSD in a network environment
with layer 2 devices which snoop IGMP traffic to mitigate multicast propagation throughout the
network. This sysctl is normally enabled by default.
net.inet.igmp.sendra
If this variable is non-zero, then IGMP v2 and v3 reports will contain the IP Router Alert option.
This sysctl is normally enabled by default.
net.inet.igmp.recvifkludge
If this variable is non-zero, then received IGMP reports which contain 0.0.0.0 as their source will
be rewritten to contain the subnet address. This is useful when there are hosts on-link which have
not yet been configured with a primary IPv4 address. This sysctl is normally enabled by default.
SEE ALSO
netstat(1), sourcefilter(3), inet(4), multicast(4), ifmcstat(8)
HISTORY
The igmp manual page re-appeared in FreeBSD 8.0.