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32 .\" @(#)icmp.4 8.1 (Berkeley) 6/5/93
40 .Nd Internet Control Message Protocol
46 .Fn socket AF_INET SOCK_RAW proto
49 is the error and control message protocol used
52 and the Internet protocol family.
56 for network monitoring
57 and diagnostic functions.
60 parameter to the socket call to create an
64 .Xr getprotobyname 3 .
66 sockets are connectionless,
67 and are normally used with the
73 call may also be used to fix the destination for future
74 packets (in which case the
82 system calls may be used).
84 Outgoing packets automatically have an
87 them (based on the destination address).
88 Incoming packets are received with the
90 header and options intact.
94 protocol implements a number of variables in the
99 .Bl -tag -width ".Va icmplim_output"
102 Enable/disable replies to ICMP Address Mask Request packets.
105 .Pq Vt "unsigned integer"
108 is set and this value is non-zero,
109 it will be used instead of the real address mask when
110 the system replies to an ICMP Address Mask Request packet.
114 Bandwidth limit for ICMP replies in packets/second.
119 .It Va icmplim_output
121 Enable/disable bandwidth limiting of ICMP replies.
125 Enable/disable dropping of ICMP Redirect packets.
129 Enable/disable logging of ICMP Redirect packets.
133 Enable/disable ICMP replies received via broadcast or multicast.
137 An interface name used for the ICMP reply source in response to packets
138 which are not directly addressed to us.
139 By default continue with normal source selection.
140 .It Va reply_from_interface
142 Use the IP address of the interface the packet came through in for
143 responses to packets which are not directly addressed to us.
144 If enabled, this rule is processed before all others.
145 By default, continue with normal source selection.
146 Enabling this option is particularly useful on routers because it
147 makes external traceroutes show the actual path a packet has taken
148 instead of the possibly different return path.
151 Number of bytes from original packet to quote in ICMP reply.
152 This number is internally enforced to be at least 8 bytes (per RFC792)
153 and at most the maximal space left in the ICMP reply mbuf.
156 A socket operation may fail with one of the following errors returned:
159 when trying to establish a connection on a socket which
160 already has one, or when trying to send a datagram with the destination
161 address specified and the socket is already connected;
163 when trying to send a datagram, but
164 no destination address is specified, and the socket has not been
167 when the system runs out of memory for
168 an internal data structure;
169 .It Bq Er EADDRNOTAVAIL
170 when an attempt is made to create a
171 socket with a network address for which no network interface