253 lines
8.5 KiB
Groff
253 lines
8.5 KiB
Groff
.\" Copyright (c) 1986, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)icmp.4 8.1 (Berkeley) 6/5/93
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.\" $FreeBSD$
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.\"
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.Dd March 26, 2015
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.Dt ICMP 4
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.Os
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.Sh NAME
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.Nm icmp
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.Nd Internet Control Message Protocol
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/socket.h
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.In netinet/in.h
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.Ft int
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.Fn socket AF_INET SOCK_RAW proto
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.Sh DESCRIPTION
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.Tn ICMP
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is the error and control message protocol used
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by
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.Tn IP
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and the Internet protocol family.
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It may be accessed
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through a
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.Dq raw socket
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for network monitoring
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and diagnostic functions.
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The
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.Fa proto
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parameter to the socket call to create an
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.Tn ICMP
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socket
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is obtained from
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.Xr getprotobyname 3 .
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.Tn ICMP
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sockets are connectionless,
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and are normally used with the
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.Xr sendto 2
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and
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.Xr recvfrom 2
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calls, though the
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.Xr connect 2
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call may also be used to fix the destination for future
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packets (in which case the
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.Xr read 2
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or
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.Xr recv 2
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and
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.Xr write 2
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or
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.Xr send 2
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system calls may be used).
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.Pp
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Outgoing packets automatically have an
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.Tn IP
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header prepended to
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them (based on the destination address).
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Incoming packets are received with the
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.Tn IP
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header and options intact.
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.Ss Types
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ICMP messages are classified according to the type and code fields
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present in the ICMP header.
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The abbreviations for the types and codes may be used in rules in
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.Xr pf.conf 5 .
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The following types are defined:
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.Bl -column x xxxxxxxxxxxx -offset indent
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.It Sy Num Ta Sy Abbrev. Ta Sy Description
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.It 0 Ta echorep Ta "Echo reply"
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.It 3 Ta unreach Ta "Destination unreachable"
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.It 4 Ta squench Ta "Packet loss, slow down"
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.It 5 Ta redir Ta "Shorter route exists"
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.It 6 Ta althost Ta "Alternate host address"
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.It 8 Ta echoreq Ta "Echo request"
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.It 9 Ta routeradv Ta "Router advertisement"
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.It 10 Ta routersol Ta "Router solicitation"
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.It 11 Ta timex Ta "Time exceeded"
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.It 12 Ta paramprob Ta "Invalid IP header"
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.It 13 Ta timereq Ta "Timestamp request"
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.It 14 Ta timerep Ta "Timestamp reply"
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.It 15 Ta inforeq Ta "Information request"
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.It 16 Ta inforep Ta "Information reply"
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.It 17 Ta maskreq Ta "Address mask request"
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.It 18 Ta maskrep Ta "Address mask reply"
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.It 30 Ta trace Ta Traceroute
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.It 31 Ta dataconv Ta "Data conversion problem"
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.It 32 Ta mobredir Ta "Mobile host redirection"
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.It 33 Ta ipv6-where Ta "IPv6 where-are-you"
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.It 34 Ta ipv6-here Ta "IPv6 i-am-here"
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.It 35 Ta mobregreq Ta "Mobile registration request"
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.It 36 Ta mobregrep Ta "Mobile registration reply"
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.It 39 Ta skip Ta SKIP
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.It 40 Ta photuris Ta Photuris
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.El
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.Pp
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The following codes are defined:
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.Bl -column x xxxxxxxxxxxx xxxxxxxx -offset indent
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.It Sy Num Ta Sy Abbrev. Ta Sy Type Ta Sy Description
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.It 0 Ta net-unr Ta unreach Ta "Network unreachable"
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.It 1 Ta host-unr Ta unreach Ta "Host unreachable"
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.It 2 Ta proto-unr Ta unreach Ta "Protocol unreachable"
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.It 3 Ta port-unr Ta unreach Ta "Port unreachable"
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.It 4 Ta needfrag Ta unreach Ta "Fragmentation needed but DF bit set"
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.It 5 Ta srcfail Ta unreach Ta "Source routing failed"
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.It 6 Ta net-unk Ta unreach Ta "Network unknown"
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.It 7 Ta host-unk Ta unreach Ta "Host unknown"
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.It 8 Ta isolate Ta unreach Ta "Host isolated"
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.It 9 Ta net-prohib Ta unreach Ta "Network administratively prohibited"
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.It 10 Ta host-prohib Ta unreach Ta "Host administratively prohibited"
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.It 11 Ta net-tos Ta unreach Ta "Invalid TOS for network"
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.It 12 Ta host-tos Ta unreach Ta "Invalid TOS for host"
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.It 13 Ta filter-prohib Ta unreach Ta "Prohibited access"
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.It 14 Ta host-preced Ta unreach Ta "Precedence violation"
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.It 15 Ta cutoff-preced Ta unreach Ta "Precedence cutoff"
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.It 0 Ta redir-net Ta redir Ta "Shorter route for network"
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.It 1 Ta redir-host Ta redir Ta "Shorter route for host"
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.It 2 Ta redir-tos-net Ta redir Ta "Shorter route for TOS and network"
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.It 3 Ta redir-tos-host Ta redir Ta "Shorter route for TOS and host"
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.It 0 Ta normal-adv Ta routeradv Ta "Normal advertisement"
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.It 16 Ta common-adv Ta routeradv Ta "Selective advertisement"
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.It 0 Ta transit Ta timex Ta "Time exceeded in transit"
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.It 1 Ta reassemb Ta timex Ta "Time exceeded in reassembly"
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.It 0 Ta badhead Ta paramprob Ta "Invalid option pointer"
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.It 1 Ta optmiss Ta paramprob Ta "Missing option"
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.It 2 Ta badlen Ta paramprob Ta "Invalid length"
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.It 1 Ta unknown-ind Ta photuris Ta "Unknown security index"
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.It 2 Ta auth-fail Ta photuris Ta "Authentication failed"
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.It 3 Ta decrypt-fail Ta photuris Ta "Decryption failed"
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.El
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.Ss MIB Variables
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The
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.Tn ICMP
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protocol implements a number of variables in the
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.Va net.inet.icmp
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branch of the
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.Xr sysctl 3
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MIB.
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.Bl -tag -width ".Va icmplim_output"
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.It Va maskrepl
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.Pq Vt boolean
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Enable/disable replies to ICMP Address Mask Request packets.
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Defaults to false.
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.It Va maskfake
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.Pq Vt "unsigned integer"
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When
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.Va maskrepl
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is set and this value is non-zero,
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it will be used instead of the real address mask when
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the system replies to an ICMP Address Mask Request packet.
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Defaults to 0.
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.It Va icmplim
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.Pq Vt integer
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Bandwidth limit for ICMP replies in packets/second.
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If set to zero, no limiting will occur.
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Defaults to 200.
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.It Va icmplim_output
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.Pq Vt boolean
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Enable/disable logging of ICMP replies bandwidth limiting.
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Defaults to true.
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.It Va drop_redirect
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.Pq Vt boolean
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Enable/disable dropping of ICMP Redirect packets.
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Defaults to false.
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.It Va log_redirect
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.Pq Vt boolean
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Enable/disable logging of ICMP Redirect packets.
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Defaults to false.
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.It Va bmcastecho
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.Pq Vt boolean
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Enable/disable ICMP replies received via broadcast or multicast.
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Defaults to false.
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.It Va reply_src
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.Pq Vt str
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An interface name used for the ICMP reply source in response to packets
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which are not directly addressed to us.
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By default continue with normal source selection.
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.It Va reply_from_interface
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.Pq Vt boolean
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Use the IP address of the interface the packet came through in for
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responses to packets which are not directly addressed to us.
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If enabled, this rule is processed before all others.
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By default, continue with normal source selection.
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Enabling this option is particularly useful on routers because it
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makes external traceroutes show the actual path a packet has taken
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instead of the possibly different return path.
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.It Va quotelen
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.Pq Vt integer
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Number of bytes from original packet to quote in ICMP reply.
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This number is internally enforced to be at least 8 bytes (per RFC792)
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and at most the maximal space left in the ICMP reply mbuf.
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.It Va tstamprepl
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.Pq Vt boolean
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Enable/disable replies to ICMP Timestamp packets.
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Defaults to true.
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.El
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.Sh ERRORS
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A socket operation may fail with one of the following errors returned:
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.Bl -tag -width Er
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.It Bq Er EISCONN
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when trying to establish a connection on a socket which
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already has one, or when trying to send a datagram with the destination
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address specified and the socket is already connected;
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.It Bq Er ENOTCONN
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when trying to send a datagram, but
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no destination address is specified, and the socket has not been
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connected;
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.It Bq Er ENOBUFS
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when the system runs out of memory for
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an internal data structure;
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.It Bq Er EADDRNOTAVAIL
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when an attempt is made to create a
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socket with a network address for which no network interface
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exists.
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.El
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.Sh SEE ALSO
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.Xr recv 2 ,
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.Xr send 2 ,
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.Xr inet 4 ,
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.Xr intro 4 ,
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.Xr ip 4 ,
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.Xr pf.conf 5
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.Sh HISTORY
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The
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.Nm
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protocol appeared in
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.Bx 4.3 .
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