IGMP(4) 						   BSD Kernel Interfaces Manual 						   IGMP(4)

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 communi-
     cate 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 pro-
	     cessing 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 behav-
	     iour 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 sub-
	     net 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.

BSD
								   March 9, 2009							       BSD