1ICMP(7) Linux Programmer's Manual ICMP(7)
2
6 icmp, IPPROTO_ICMP - Linux IPv4 ICMP kernel module.
7
9 This kernel protocol module implements the Internet Control Message
10 Protocol defined in RFC 792. It is used to signal error conditions and
11 for diagnosis. The user doesn't interact directly with this module;
12 instead it communicates with the other protocols in the kernel and
13 these pass the ICMP errors to the application layers. The kernel ICMP
14 module also answers ICMP requests.
15 A user protocol may receive ICMP packets for all local sockets by open‐
17 ing a raw socket with the protocol IPPROTO_ICMP. See raw(7) for more
18 information. The types of ICMP packets passed to the socket can be
19 filtered using the ICMP_FILTER socket option. ICMP packets are always
20 processed by the kernel too, even when passed to a user socket.
21 Linux limits the rate of ICMP error packets to each destination.
23 ICMP_REDIRECT and ICMP_DEST_UNREACH are also limited by the destination
24 route of the incoming packets.
25
27 ICMP supports a sysctl interface to configure some global IP parame‐
28 ters. The sysctls can be accessed by reading or writing the
29 /proc/sys/net/ipv4/* files or with the sysctl(2) interface. Most of
30 these sysctls are rate limitations for specific ICMP types. Linux 2.2
31 uses a token bucket filter to limit ICMPs. The value is the timeout in
32 jiffies until the token bucket filter is cleared after a burst. A
33 jiffy is a system dependent unit, usually 10ms on x86 and about 1ms on
34 alpha and IA64.
35 icmp_destunreach_rate
37 Maximum rate to send ICMP Destination Unreachable packets. This
38 limits the rate at which packets are sent to any individual
39 route or destination. The limit does not affect sending of
40 ICMP_FRAG_NEEDED packets needed for path MTU discovery.
41 icmp_echo_ignore_all
43 If this value is non-zero, Linux will ignore all ICMP_ECHO
44 requests.
45 icmp_echo_ignore_broadcasts
47 If this value is non-zero, Linux will ignore all ICMP_ECHO pack‐
48 ets sent to broadcast addresses.
49 icmp_echoreply_rate
51 Maximum rate for sending ICMP_ECHOREPLY packets in response to
52 ICMP_ECHOREQUEST packets.
53 icmp_paramprob_rate
55 Maximum rate for sending ICMP_PARAMETERPROB packets. These
56 packets are sent when a packet arrives with an invalid IP
57 header.
58 icmp_timeexceed_rate
60 Maximum rate for sending ICMP_TIME_EXCEEDED packets. These
61 packets are sent to prevent loops when a packet has crossed too
62 many hops.
63
65 As many other implementations don't support IPPROTO_ICMP raw sockets,
66 this feature should not be relied on in portable programs.
67 ICMP_REDIRECT packets are not sent when Linux is not acting as a
69 router. They are also only accepted from the old gateway defined in
70 the routing table and the redirect routes are expired after some time.
71 The 64-bit timestamp returned by ICMP_TIMESTAMP is in milliseconds
73 since January 1, 1970.
74 Linux ICMP internally uses a raw socket to send ICMPs. This raw socket
76 may appear in netstat(8) output with a zero inode.
77
79 Support for the ICMP_ADDRESS request was removed in 2.2.
80 Support for ICMP_SOURCE_QUENCH was removed in Linux 2.2.
82
84 ip(7)
85 RFC 792 for a description of the ICMP protocol.
87Linux Man Page 1999-04-27 ICMP(7)