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.

Debian                                            March 9, 2009                                          IGMP(4)