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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.