NAME¶
icmp
—
Internet Control Message Protocol
SYNOPSIS¶
#include
<sys/types.h>
#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 |
MIB Variables¶
The ICMP protocol implements a number of variables in the
net.inet.icmp branch of the
sysctl(3) MIB.
- maskrepl
- (boolean) Enable/disable replies to ICMP
Address Mask Request packets. Defaults to false.
- maskfake
- (unsigned integer) When
maskrepl is set and this value is
non-zero, it will be used instead of the real address mask when the system
replies to an ICMP Address Mask Request packet. Defaults to 0.
- icmplim
- (integer) Bandwidth limit for ICMP
replies in packets/second. Used when
icmplim_output is non-zero. Defaults to
200.
- icmplim_output
- (boolean) Enable/disable bandwidth
limiting of ICMP replies. Defaults to true.
- drop_redirect
- (boolean) Enable/disable dropping of ICMP
Redirect packets. Defaults to false.
- log_redirect
- (boolean) Enable/disable logging of ICMP
Redirect packets. Defaults to false.
- bmcastecho
- (boolean) Enable/disable ICMP replies
received via broadcast or multicast. Defaults to false.
- reply_src
- (str) An interface name used for the ICMP
reply source in response to packets which are not directly addressed to
us. By default continue with normal source selection.
- reply_from_interface
- (boolean) Use the IP address of the
interface the packet came through in for responses to packets which are
not directly addressed to us. If enabled, this rule is processed before
all others. By default, continue with normal source selection. Enabling
this option is particularly useful on routers because it makes external
traceroutes show the actual path a packet has taken instead of the
possibly different return path.
- quotelen
- (integer) Number of bytes from original
packet to quote in ICMP reply. This number is internally enforced to be at
least 8 bytes (per RFC792) and at most the maximal space left in the ICMP
reply mbuf.
ERRORS¶
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 has not 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¶
recv(2),
send(2),
inet(4),
intro(4),
ip(4),
pf.conf(5)
HISTORY¶
The
icmp
protocol appeared in
4.3BSD.