1.\" 2.\" Copyright (c) 2009 Bruce Simpson. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. Neither the name of the project nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" $FreeBSD$ 29.\" 30.Dd March 9, 2009 31.Dt IGMP 4 32.Os 33.Sh NAME 34.Nm igmp 35.Nd Internet Group Management Protocol 36.Sh SYNOPSIS 37.In sys/types.h 38.In sys/socket.h 39.In netinet/in.h 40.In netinet/in_systm.h 41.In netinet/ip.h 42.In netinet/igmp.h 43.Ft int 44.Fn socket AF_INET SOCK_RAW IPPROTO_IGMP 45.Sh DESCRIPTION 46.Tn IGMP 47is a control plane protocol used by IPv4 hosts and routers to 48propagate multicast group membership information. 49Normally this protocol is not used directly, except by the kernel 50itself, in response to multicast membership requests by user 51applications. 52Routing protocols may open a raw socket to directly interact with 53.Nm . 54.Pp 55As of 56.Fx 8.0 , 57IGMP version 3 is implemented. 58This adds support for Source-Specific Multicast (SSM), whereby 59applications may communicate to upstream multicast routers that 60they are only interested in receiving multicast streams from 61particular sources. 62.\" 63.Sh SYSCTL VARIABLES 64.Bl -tag -width indent 65.\" 66.It net.inet.igmp.stats 67This opaque read-only variable exposes the stack-wide IGMPv3 68protocol statistics to 69.Xr netstat 1 . 70.\" 71.It net.inet.igmp.ifinfo 72This opaque read-only variable exposes the per-link IGMPv3 status to 73.Xr ifmcstat 8 . 74.\" 75.It net.inet.igmp.gsrdelay 76This variable specifies the time threshold, in seconds, for processing 77Group-and-Source Specific Queries (GSR). 78As GSR query processing requires maintaining state on the host, 79it may cause memory to be allocated, and is therefore a potential 80attack point for Denial-of-Service (DoS). 81If more than one GSR query is received within this threshold, 82it will be dropped, to mitigate the potential for DoS. 83.\" 84.It net.inet.igmp.default_version 85This variable controls the default version of IGMP to be used on all links. 86This sysctl is normally set to 3 by default. 87.\" 88.It net.inet.igmp.legacysupp 89If this variable is non-zero, then IGMP v1 and v2 membership reports 90received on a link will be allowed to suppress the IGMP v3 state-change 91reports which would otherwise be issued by this host. 92This sysctl is normally enabled by default. 93.\" 94.It net.inet.igmp.v2enable 95If this variable is non-zero, then IGMP v2 membership queries will be 96processed by this host, and backwards compatibility will be enabled 97until the v2 'Old Querier Present' timer expires. 98This sysctl is normally enabled by default. 99.\" 100.It net.inet.igmp.v1enable 101If this variable is non-zero, then IGMP v1 membership queries will be 102processed by this host, and backwards compatibility will be enabled 103until the v1 'Old Querier Present' timer expires. 104This sysctl is normally enabled by default. 105.\" 106.It net.inet.igmp.sendlocal 107If this variable is non-zero, then IGMP state-changes for groups in 108the 224.0.0.0/24 link-scope prefix will be issued. 109This behaviour is recommended if deploying 110.Fx 111in a network environment with layer 2 devices which snoop IGMP traffic 112to mitigate multicast propagation throughout the network. 113This sysctl is normally enabled by default. 114.\" 115.It net.inet.igmp.sendra 116If this variable is non-zero, then IGMP v2 and v3 reports will contain 117the IP Router Alert option. 118This sysctl is normally enabled by default. 119.\" 120.It net.inet.igmp.recvifkludge 121If this variable is non-zero, then received IGMP reports which contain 1220.0.0.0 as their source will be rewritten to contain the subnet address. 123This is useful when there are hosts on-link which have not yet been 124configured with a primary IPv4 address. 125This sysctl is normally enabled by default. 126.\" 127.El 128.Sh SEE ALSO 129.Xr netstat 1 , 130.Xr sourcefilter 3 , 131.Xr inet 4 , 132.Xr multicast 4 , 133.Xr ifmcstat 8 134.Sh HISTORY 135The 136.Nm 137manual page re-appeared in 138.Fx 8.0 . 139