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.Dd March 9, 2009 29.Dt IGMP 4 30.Os 31.Sh NAME 32.Nm igmp 33.Nd Internet Group Management Protocol 34.Sh SYNOPSIS 35.In sys/types.h 36.In sys/socket.h 37.In netinet/in.h 38.In netinet/in_systm.h 39.In netinet/ip.h 40.In netinet/igmp.h 41.Ft int 42.Fn socket AF_INET SOCK_RAW IPPROTO_IGMP 43.Sh DESCRIPTION 44.Tn IGMP 45is a control plane protocol used by IPv4 hosts and routers to 46propagate multicast group membership information. 47Normally this protocol is not used directly, except by the kernel 48itself, in response to multicast membership requests by user 49applications. 50Routing protocols may open a raw socket to directly interact with 51.Nm . 52.Pp 53As of 54.Fx 8.0 , 55IGMP version 3 is implemented. 56This adds support for Source-Specific Multicast (SSM), whereby 57applications may communicate to upstream multicast routers that 58they are only interested in receiving multicast streams from 59particular sources. 60.\" 61.Sh SYSCTL VARIABLES 62.Bl -tag -width indent 63.\" 64.It net.inet.igmp.stats 65This opaque read-only variable exposes the stack-wide IGMPv3 66protocol statistics to 67.Xr netstat 1 . 68.\" 69.It net.inet.igmp.ifinfo 70This opaque read-only variable exposes the per-link IGMPv3 status to 71.Xr ifmcstat 8 . 72.\" 73.It net.inet.igmp.gsrdelay 74This variable specifies the time threshold, in seconds, for processing 75Group-and-Source Specific Queries (GSR). 76As GSR query processing requires maintaining state on the host, 77it may cause memory to be allocated, and is therefore a potential 78attack point for Denial-of-Service (DoS). 79If more than one GSR query is received within this threshold, 80it will be dropped, to mitigate the potential for DoS. 81.\" 82.It net.inet.igmp.default_version 83This variable controls the default version of IGMP to be used on all links. 84This sysctl is normally set to 3 by default. 85.\" 86.It net.inet.igmp.legacysupp 87If this variable is non-zero, then IGMP v1 and v2 membership reports 88received on a link will be allowed to suppress the IGMP v3 state-change 89reports which would otherwise be issued by this host. 90This sysctl is normally enabled by default. 91.\" 92.It net.inet.igmp.v2enable 93If this variable is non-zero, then IGMP v2 membership queries will be 94processed by this host, and backwards compatibility will be enabled 95until the v2 'Old Querier Present' timer expires. 96This sysctl is normally enabled by default. 97.\" 98.It net.inet.igmp.v1enable 99If this variable is non-zero, then IGMP v1 membership queries will be 100processed by this host, and backwards compatibility will be enabled 101until the v1 'Old Querier Present' timer expires. 102This sysctl is normally enabled by default. 103.\" 104.It net.inet.igmp.sendlocal 105If this variable is non-zero, then IGMP state-changes for groups in 106the 224.0.0.0/24 link-scope prefix will be issued. 107This behaviour is recommended if deploying 108.Fx 109in a network environment with layer 2 devices which snoop IGMP traffic 110to mitigate multicast propagation throughout the network. 111This sysctl is normally enabled by default. 112.\" 113.It net.inet.igmp.sendra 114If this variable is non-zero, then IGMP v2 and v3 reports will contain 115the IP Router Alert option. 116This sysctl is normally enabled by default. 117.\" 118.It net.inet.igmp.recvifkludge 119If this variable is non-zero, then received IGMP reports which contain 1200.0.0.0 as their source will be rewritten to contain the subnet address. 121This is useful when there are hosts on-link which have not yet been 122configured with a primary IPv4 address. 123This sysctl is normally enabled by default. 124.\" 125.El 126.Sh SEE ALSO 127.Xr netstat 1 , 128.Xr sourcefilter 3 , 129.Xr inet 4 , 130.Xr multicast 4 , 131.Xr ifmcstat 8 132.Sh HISTORY 133The 134.Nm 135manual page re-appeared in 136.Fx 8.0 . 137