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.