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33 .Nd Internet Group Management Protocol
38 .In netinet/in_systm.h
42 .Fn socket AF_INET SOCK_RAW IPPROTO_IGMP
45 is a control plane protocol used by IPv4 hosts and routers to
46 propagate multicast group membership information.
47 Normally this protocol is not used directly, except by the kernel
48 itself, in response to multicast membership requests by user
50 Routing protocols may open a raw socket to directly interact with
55 IGMP version 3 is implemented.
56 This adds support for Source-Specific Multicast (SSM), whereby
57 applications may communicate to upstream multicast routers that
58 they are only interested in receiving multicast streams from
62 .Bl -tag -width indent
64 .It net.inet.igmp.stats
65 This opaque read-only variable exposes the stack-wide IGMPv3
66 protocol statistics to
69 .It net.inet.igmp.ifinfo
70 This opaque read-only variable exposes the per-link IGMPv3 status to
73 .It net.inet.igmp.gsrdelay
74 This variable specifies the time threshold, in seconds, for processing
75 Group-and-Source Specific Queries (GSR).
76 As GSR query processing requires maintaining state on the host,
77 it may cause memory to be allocated, and is therefore a potential
78 attack point for Denial-of-Service (DoS).
79 If more than one GSR query is received within this threshold,
80 it will be dropped, to mitigate the potential for DoS.
82 .It net.inet.igmp.default_version
83 This variable controls the default version of IGMP to be used on all links.
84 This sysctl is normally set to 3 by default.
86 .It net.inet.igmp.legacysupp
87 If this variable is non-zero, then IGMP v1 and v2 membership reports
88 received on a link will be allowed to suppress the IGMP v3 state-change
89 reports which would otherwise be issued by this host.
90 This sysctl is normally enabled by default.
92 .It net.inet.igmp.v2enable
93 If this variable is non-zero, then IGMP v2 membership queries will be
94 processed by this host, and backwards compatibility will be enabled
95 until the v2 'Old Querier Present' timer expires.
96 This sysctl is normally enabled by default.
98 .It net.inet.igmp.v1enable
99 If this variable is non-zero, then IGMP v1 membership queries will be
100 processed by this host, and backwards compatibility will be enabled
101 until the v1 'Old Querier Present' timer expires.
102 This sysctl is normally enabled by default.
104 .It net.inet.igmp.sendlocal
105 If this variable is non-zero, then IGMP state-changes for groups in
106 the 224.0.0.0/24 link-scope prefix will be issued.
107 This behaviour is recommended if deploying
109 in a network environment with layer 2 devices which snoop IGMP traffic
110 to mitigate multicast propagation throughout the network.
111 This sysctl is normally enabled by default.
113 .It net.inet.igmp.sendra
114 If this variable is non-zero, then IGMP v2 and v3 reports will contain
115 the IP Router Alert option.
116 This sysctl is normally enabled by default.
118 .It net.inet.igmp.recvifkludge
119 If this variable is non-zero, then received IGMP reports which contain
120 0.0.0.0 as their source will be rewritten to contain the subnet address.
121 This is useful when there are hosts on-link which have not yet been
122 configured with a primary IPv4 address.
123 This sysctl is normally enabled by default.
135 manual page re-appeared in