NAME
icmp
—
Internet Control Message
Protocol
SYNOPSIS
#include
<sys/socket.h>
#include <netinet/in.h>
int
socket
(AF_INET,
SOCK_RAW,
proto);
DESCRIPTION
ICMP is the error and control message protocol used by IP and the Internet protocol family. It may be accessed through a “raw socket” for network monitoring and diagnostic functions. The proto parameter to the socket call to create an ICMP socket is obtained from getprotobyname(3). ICMP sockets are connectionless, and are normally used with the sendto(2) and recvfrom(2) calls, though the connect(2) call may also be used to fix the destination for future packets (in which case the read(2) or recv(2) and write(2) or send(2) system calls may be used).
Outgoing packets automatically have an IP header prepended to them (based on the destination address). Incoming packets are received with the IP header and options intact.
Types
ICMP messages are classified according to the type and code fields present in the ICMP header. The abbreviations for the types and codes may be used in rules in pf.conf(5). The following types are defined:
Num | Abbrev. | Description |
0 | echorep | Echo reply |
3 | unreach | Destination unreachable |
4 | squench | Packet loss, slow down |
5 | redir | Shorter route exists |
6 | althost | Alternate host address |
8 | echoreq | Echo request |
9 | routeradv | Router advertisement |
10 | routersol | Router solicitation |
11 | timex | Time exceeded |
12 | paramprob | Invalid IP header |
13 | timereq | Timestamp request |
14 | timerep | Timestamp reply |
15 | inforeq | Information request |
16 | inforep | Information reply |
17 | maskreq | Address mask request |
18 | maskrep | Address mask reply |
30 | trace | Traceroute |
31 | dataconv | Data conversion problem |
32 | mobredir | Mobile host redirection |
33 | ipv6-where | IPv6 where-are-you |
34 | ipv6-here | IPv6 i-am-here |
35 | mobregreq | Mobile registration request |
36 | mobregrep | Mobile registration reply |
39 | skip | SKIP |
40 | photuris | Photuris |
The following codes are defined:
Num | Abbrev. | Type | Description |
0 | net-unr | unreach | Network unreachable |
1 | host-unr | unreach | Host unreachable |
2 | proto-unr | unreach | Protocol unreachable |
3 | port-unr | unreach | Port unreachable |
4 | needfrag | unreach | Fragmentation needed but DF bit set |
5 | srcfail | unreach | Source routing failed |
6 | net-unk | unreach | Network unknown |
7 | host-unk | unreach | Host unknown |
8 | isolate | unreach | Host isolated |
9 | net-prohib | unreach | Network administratively prohibited |
10 | host-prohib | unreach | Host administratively prohibited |
11 | net-tos | unreach | Invalid TOS for network |
12 | host-tos | unreach | Invalid TOS for host |
13 | filter-prohib | unreach | Prohibited access |
14 | host-preced | unreach | Precedence violation |
15 | cutoff-preced | unreach | Precedence cutoff |
0 | redir-net | redir | Shorter route for network |
1 | redir-host | redir | Shorter route for host |
2 | redir-tos-net | redir | Shorter route for TOS and network |
3 | redir-tos-host | redir | Shorter route for TOS and host |
0 | normal-adv | routeradv | Normal advertisement |
16 | common-adv | routeradv | Selective advertisement |
0 | transit | timex | Time exceeded in transit |
1 | reassemb | timex | Time exceeded in reassembly |
0 | badhead | paramprob | Invalid option pointer |
1 | optmiss | paramprob | Missing option |
2 | badlen | paramprob | Invalid length |
1 | unknown-ind | photuris | Unknown security index |
2 | auth-fail | photuris | Authentication failed |
3 | decrypt-fail | photuris | Decryption failed |
DIAGNOSTICS
A socket operation may fail with one of the following errors returned:
- [
EISCONN
] - when trying to establish a connection on a socket which already has one, or when trying to send a datagram with the destination address specified and the socket is already connected;
- [
ENOTCONN
] - when trying to send a datagram, but no destination address is specified, and the socket hasn't been connected;
- [
ENOBUFS
] - when the system runs out of memory for an internal data structure;
- [
EADDRNOTAVAIL
] - when an attempt is made to create a socket with a network address for which no network interface exists.
SEE ALSO
HISTORY
The icmp
protocol appeared in
4.3BSD.