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icmp — Linux IPv4 ICMP kernel module.
This kernel protocol module implements the Internet Control Message Protocol defined in RFC 792. It is used to signal error conditions and for diagnosis. The user doesn't interact directly with this module; instead it communicates with the other protocols in the kernel and these pass the ICMP errors to the application layers. The kernel ICMP module also answers ICMP requests.
A user protocol may receive ICMP packets for all local
sockets by opening a raw socket with the protocol
IPPROTO_ICMP. See raw(7) for more
information. The types of ICMP packets passed to the socket
can be filtered using the ICMP_FILTER socket option. ICMP packets are
always processed by the kernel too, even when passed to a
user socket.
Linux limits the rate of ICMP error packets to each
destination. ICMP_REDIRECT and
ICMP_DEST_UNREACH are also
limited by the destination route of the incoming packets.
ICMP supports a set of /proc interfaces to configure some global
IP parameters. The parameters can be accessed by reading or
writing files in the directory /proc/sys/net/ipv4/. Most of these
parameters are rate limitations for specific ICMP types.
Linux 2.2 uses a token bucket filter to limit ICMPs. The
value is the timeout in jiffies until the token bucket
filter is cleared after a burst. A jiffy is a system
dependent unit, usually 10ms on i386 and about 1ms on alpha
and ia64.
icmp_destunreach_rate
(Linux 2.2 to 2.4.9)Maximum rate to send ICMP Destination Unreachable
packets. This limits the rate at which packets are
sent to any individual route or destination. The
limit does not affect sending of ICMP_FRAG_NEEDED packets needed for
path MTU discovery.
icmp_echo_ignore_all
(since Linux 2.2)If this value is nonzero, Linux will ignore all
ICMP_ECHO requests.
icmp_echo_ignore_broadcasts
(since Linux 2.2)If this value is nonzero, Linux will ignore all
ICMP_ECHO packets sent
to broadcast addresses.
icmp_echoreply_rate
(Linux 2.2 to 2.4.9)Maximum rate for sending ICMP_ECHOREPLY packets in response
to ICMP_ECHOREQUEST
packets.
icmp_errors_use_inbound_ifaddr
(Boolean; default: disabled; since Linux
2.6.12)If disabled, ICMP error messages are sent with the primary address of the exiting interface.
If enabled, the message will be sent with the primary address of the interface that received the packet that caused the ICMP error. This is the behavior that many network administrators will expect from a router. And it can make debugging complicated network layouts much easier.
Note that if no primary address exists for the interface selected, then the primary address of the first non-loopback interface that has one will be used regardless of this setting.
icmp_ignore_bogus_error_responses
(Boolean; default: disabled; since Linux
2.2)Some routers violate RFC1122 by sending bogus responses to broadcast frames. Such violations are normally logged via a kernel warning. If this parameter is enabled, the kernel will not give such warnings, which will avoid log file clutter.
icmp_paramprob_rate
(Linux 2.2 to 2.4.9)Maximum rate for sending ICMP_PARAMETERPROB packets. These
packets are sent when a packet arrives with an
invalid IP header.
icmp_ratelimit
(integer; default: 1000; since Linux
2.4.10)Limit the maximum rates for sending ICMP packets
whose type matches icmp_ratemask (see
below) to specific targets. 0 to disable any
limiting, otherwise the minimum space between
responses in milliseconds.
icmp_ratemask (integer;
default: see below; since Linux 2.4.10)Mask made of ICMP types for which rates are being limited.
Significant bits: IHGFEDCBA9876543210
Default mask: 0000001100000011000 (0x1818)
Bit definitions (see the Linux kernel source file
include/linux/icmp.h):
0 Echo Reply 3 Destination Unreachable * 4 Source Quench * 5 Redirect 8 Echo Request B Time Exceeded * C Parameter Problem * D Timestamp Request E Timestamp Reply F Info Request G Info Reply H Address Mask Request I Address Mask Reply
The bits marked with an asterisk are rate limited by default (see the default mask above).
icmp_timeexceed_rate
(Linux 2.2 to 2.4.9)Maximum rate for sending ICMP_TIME_EXCEEDED packets. These
packets are sent to prevent loops when a packet has
crossed too many hops.
Support for the ICMP_ADDRESS
request was removed in 2.2.
Support for ICMP_SOURCE_QUENCH was removed in Linux
2.2.
As many other implementations don't support IPPROTO_ICMP raw sockets, this feature
should not be relied on in portable programs.
ICMP_REDIRECT packets are
not sent when Linux is not acting as a router. They are also
accepted only from the old gateway defined in the routing
table and the redirect routes are expired after some
time.
The 64-bit timestamp returned by ICMP_TIMESTAMP is in milliseconds since the
Epoch, 1970-01-01 00:00:00 +0000 (UTC).
Linux ICMP internally uses a raw socket to send ICMPs. This raw socket may appear in netstat(8) output with a zero inode.
This page is part of release 3.52 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
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This man page is Copyright (C) 1999 Andi Kleen <akmuc.de>. %%%LICENSE_START(VERBATIM_ONE_PARA) Permission is granted to distribute possibly modified copies of this page provided the header is included verbatim, and in case of nontrivial modification author and date of the modification is added to the header. %%%LICENSE_END $Id: icmp.7,v 1.6 2000/08/14 08:03:45 ak Exp $ |