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
ifmcstat(8), inet(4), multicast(4), netstat(1), sourcefilter(3)
HISTORY
The igmp manual page re-appeared in FreeBSD 8.0.