igmp man page on FreeBSD

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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 propa‐
     gate 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 pro‐
	     tocol 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 pro‐
	     cessing 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 be‐
	     haviour is recommended if deploying FreeBSD in a network environ‐
	     ment 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.

BSD				 March 9, 2009				   BSD
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