SYNOPSIS
ping [-dfnqRrv] [-c count] [-i wait] [-l preload] [-p pattern] [-s packetsize] host
DESCRIPTION
The ping utility sends a packet to the specified host and waits for a re-
ply. The host address and round-trip times for each pair of packets are
displayed. In addition, the total number of packets sent, received, per-
cent packet loss and minimum, average and maximum round-trip times are
displayed when the program exits or when a SIGINFO signal (see the
``status'' argument for stty(1)) is received.
The options are as follows:
-c count
Stop after sending (and receiving) count packets. After count
packets have been sent, ping will wait no more than twice the
round-trip time of the last received packet (or 10 seconds if no
packets have been received) before exiting.
-d Set the SO_DEBUG option on the socket being used.
-f
Flood ping. Outputs packets as fast as they come back or one
hundred times per second, whichever is more. For every query
packet sent a period ``.'' is printed, and for every response
packet received, a backspace is printed. This provides a rapid
display of how many packets are being dropped.
Only the super-user may use this option. This can be very hard
on a network and should be used with caution.
-i wait
Pause wait seconds between sending each query packet. By de-
fault, ping waits one second between each packet.
-l preload
If preload is specified, ping sends that many packets as fast as
possible before continuing in its normal mode.
-n
Numeric output only. No attempt will be made to lookup symbolic
names for host addresses.
-p pattern
You may specify up to 16 ``pad'' bytes to fill out the packet you
send. This is useful for diagnosing data-dependent problems in a
network. For example, ``-p ff'' will cause the sent packet to be
filled with all ones.
-q
Quiet mode. Nothing is displayed except the summary lines at
startup time and when ping exits.
-R
Record route. Includes the RECORD_ROUTE option in the query
packet and displays the route buffer on returned packets. Note
that the IP header is only large enough for nine such routes, and
many hosts ignore or discard this option.
-r
Bypass the normal routing tables and send directly to a host on
an attached network. If the host is not on a directly-attached
network, an error is returned. This option can be used to ping a
local host through an interface that has no route through it
(e.g., after the interface was dropped by routed(8)).
-v
The ping utility exits 0 on success, and >0 if an error occurs or if no
response was received from the target system.
The ping utility uses the ICMP protocol's mandatory ECHO_REQUEST datagram
to elicit an ICMP ECHO_RESPONSE from a host or gateway. ECHO_REQUEST
datagrams (``pings'') have an IP and ICMP header, followed by a ``struct
timeval'' and then an arbitrary number of ``pad'' bytes used to fill out
the packet.
When using ping for fault isolation, it should first be run on the local
host, to verify that the local network interface is up and running.
Then, hosts and gateways further and further away should be ``pinged''.
Round-trip times and packet loss statistics are computed. If duplicate
packets are received, they are not included in the packet loss calcula-
tion, although the round trip time of these packets is used in calculat-
ing the minimum/average/maximum round-trip time numbers. When the speci-
fied number of packets have been sent (and received) or if the program is
terminated with a SIGINT signal, or the program receives a SIGINFO sig-
nal, a brief summary is displayed.
This program is intended for use in network testing, measurement and man-
agement. Because of the load it can impose on the network, it is unwise
to use ping during normal operations or from automated scripts without
specifying the -c option.
ICMP PACKET DETAILS
If the data space is at least eight bytes large, ping uses the first
eight bytes of this space to include a timestamp which it uses in the
computation of round trip times. If less than eight bytes of pad are
specified, no round trip times are given.
DUPLICATE AND DAMAGED PACKETS
Damaged packets are obviously serious cause for alarm and often indicate
broken hardware somewhere in the ping packet's path (in the network or in
the hosts).
TRYING DIFFERENT DATA PATTERNS
This means that if you have a data-dependent problem you will probably
have to do a lot of testing to find it. If you are lucky, you may manage
to find a file that either can't be sent across your network or that
takes much longer to transfer than other similar length files. You can
then examine this file for repeated patterns that you can test using the
-p option of ping.
TTL DETAILS
The TCP/IP specification states that the TTL field for TCP packets should
be set to 60, but many systems use smaller values (4.3 BSD uses 30, 4.2
used 15).
The maximum possible value of this field is 255, and most Unix systems
set the TTL field of ICMP ECHO_REQUEST packets to 255. This is why you
will find you can ``ping'' some hosts, but not reach them with telnet(1)
or ftp(1).
In normal operation ping prints the ttl value from the packet it re-
ceives. When a remote system receives a ping packet, it can do one of
three things with the TTL field in its response:
o Not change it; this is what Berkeley Unix systems did before the
4.3BSD-Tahoe release. In this case the TTL value in the received
packet will be 255 minus the number of routers in the round-trip
path.
o Set it to 255; this is what current Berkeley Unix systems do. In
this case the TTL value in the received packet will be 255 minus the
number of routers in the path from the remote system to the pinging
host.
o Set it to some other value. Some machines use the same value for
ICMP packets that they use for TCP packets, for example either 30 or
60. Others may use completely wild values.
BUGS
The maximum IP header length is too small for options like RECORD_ROUTE
to be completely useful. There's not much that that can be done about
this, however.
Flood pinging is not recommended in general, and flood pinging the broad-
cast address should only be done under very controlled conditions.
SEE ALSO
SYNOPSIS
DESCRIPTION
The only mandatory parameter is the destination host name or IP number.
The default probe datagram length is 38 bytes, but this may be increased
by specifying a packet size (in bytes) after the destination host name.
-m max_ttl
-n
Print hop addresses numerically rather than symbolically and nu-
merically (saves a nameserver address-to-name lookup for each
gateway found on the path).
-p port
-q nqueries
-r
-s src_addr
-t tos
-v
-w
This program attempts to trace the route an IP packet would follow to
some internet host by launching UDP probe packets with a small ttl (time
to live) then listening for an ICMP "time exceeded" reply from a gateway.
We start our probes with a ttl of one and increase by one until we get an
ICMP "port unreachable" (which means we got to "host") or hit a max
(which defaults to 30 hops & can be changed with the -m flag). Three
probes (changed with -q flag) are sent at each ttl setting and a line is
printed showing the ttl, address of the gateway and round trip time of
each probe. If the probe answers come from different gateways, the ad-
dress of each responding system will be printed. If there is no response
within a 3 sec. timeout interval (changed with the -w flag), a "*" is
printed for that probe.
We don't want the destination host to process the UDP probe packets so
the destination port is set to an unlikely value (if some clod on the
destination is using that value, it can be changed with the -p flag).
A sample use and output might be:
[yak 71]% traceroute nis.nsf.net.
Note that lines 2 & 3 are the same. This is due to a buggy kernel on the
2nd hop system - lbl-csam.arpa - that forwards packets with a zero ttl (a
bug in the distributed version of 4.3 BSD). Note that you have to guess
what path the packets are taking cross-country since the NSFNet (129.140)
doesn't supply address-to-name translations for its NSSes.
DUPLICATE AND DAMAGED PACKETS
A more interesting example is:
[yak 72]% traceroute allspice.lcs.mit.edu.
Note that the gateways 12, 14, 15, 16 & 17 hops away either don't send
ICMP "time exceeded" messages or send them with a ttl too small to reach
us. 14 - 17 are running the MIT C Gateway code that doesn't send "time
exceeded"s. God only knows what's going on with 12.
The silent gateway 12 in the above may be the result of a bug in the
4.[23] BSD network code (and its derivatives): 4.x (x <= 3) sends an un-
reachable message using whatever ttl remains in the original datagram.
Since, for gateways, the remaining ttl is zero, the ICMP "time exceeded"
is guaranteed to not make it back to us. The behavior of this bug is
slightly more interesting when it appears on the destination system:
1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
Notice that there are 12 "gateways" (13 is the final destination) and ex-
actly the last half of them are "missing". What's really happening is
that rip (a Sun-3 running Sun OS3.5) is using the ttl from our arriving
datagram as the ttl in its ICMP reply. So, the reply will time out on
the return path (with no notice sent to anyone since ICMP's aren't sent
for ICMP's) until we probe with a ttl that's at least twice the path
length. I.e., rip is really only 7 hops away. A reply that returns with
a ttl of 1 is a clue this problem exists. Traceroute prints a "!" after
the time if the ttl is <= 1. Since vendors ship a lot of obsolete (DEC's
Ultrix, Sun 3.x) or non-standard (HPUX) software, expect to see this
problem frequently and/or take care picking the target host of your
probes. Other possible annotations after the time are !H, !N, !P (got a
host, network or protocol unreachable, respectively), !S or !F (source
route failed or fragmentation needed - neither of these should ever occur
and the associated gateway is busted if you see one). If almost all the
probes result in some kind of unreachable, traceroute will give up and exit.
This program is intended for use in network testing, measurement and man-
agement. It should be used primarily for manual fault isolation. Be-
cause of the load it could impose on the network, it is unwise to use
traceroute during normal operations or from automated scripts.
bron:http://www.stopspam.org/usenet/mmf/man/index.html
Specifies the number of data bytes to be sent. The default is
56, which translates into 64 ICMP data bytes when combined with
the 8 bytes of ICMP header data.
Verbose output. This option causes ping to list ICMP packets
other than ECHO_RESPONSE that are received.
An IP header without options is 20 bytes. An ICMP ECHO_REQUEST packet
contains an additional 8 bytes worth of ICMP header followed by an arbi-
trary amount of data. When a packetsize is given, this indicated the
size of this extra piece of data (the default is 56). Thus the amount of
data received inside of an IP packet of type ICMP ECHO_REPLY will always
be 8 bytes more than the requested data space (the ICMP header).
Ping will report duplicate and damaged packets. Duplicate packets should
never occur, and seem to be caused by inappropriate link-level retrans-
missions. Duplicates may occur in many situations and are rarely (if ev-
er) a good sign, although the presence of low levels of duplicates may
not always be cause for alarm.
The (inter)network layer should never treat packets differently depending
on the data contained in the data portion. Unfortunately, data-dependent
problems have been known to sneak into networks and remain undetected for
long periods of time. In many cases the particular pattern that will
have problems is something that doesn't have sufficient ``transitions'',
such as all ones or all zeros, or a pattern right at the edge, such as
almost all zeros. It isn't necessarily enough to specify a data pattern
of all zeros (for example) on the command line because the pattern that
is of interest is at the data link level, and the relationship between
what you type and what the controllers transmit can be complicated.
The TTL value of an IP packet represents the maximum number of IP routers
that the packet can go through before being thrown away. In current
practice you can expect each router in the Internet to decrement the TTL
field by exactly one.
Many Hosts and Gateways ignore the RECORD_ROUTE option.
netstat(1), ifconfig(8), routed(8), traceroute(8)
NAME
traceroute - print the route packets take to network host
traceroute [-m max_ttl] [-n] [-p port] [-q nqueries] [-r] [-s src_addr]
[-t tos] [-w waittime] host [packetsize]
The Internet is a large and complex aggregation of network hardware, con-
nected together by gateways. Tracking the route one's packets follow (or
finding the miscreant gateway that's discarding your packets) can be dif-
ficult. Traceroute utilizes the IP protocol `time to live' field and at-
tempts to elicit an ICMP TIME_EXCEEDED response from each gateway along
the path to some host.
The options are as follows:
Set the max time-to-live (max number of hops) used in outgoing
probe packets. The default is 30 hops (the same default used for
TCP connections).
Set the base UDP port number used in probes (default is 33434).
Traceroute hopes that nothing is listening on UDP ports base to
base+nhops-1 at the destination host (so an ICMP PORT_UNREACHABLE
message will be returned to terminate the route tracing). If
something is listening on a port in the default range, this op-
tion can be used to pick an unused port range.
Set the number of probes per ``ttl'' to nqueries (default is
three probes).
Bypass the normal routing tables and send directly to a host on
an attached network. If the host is not on a directly-attached
network, an error is returned. This option can be used to ping a
local host through an interface that has no route through it
(e.g., after the interface was dropped by routed(8)).
Use the following IP address (which must be given as an IP num-
ber, not a hostname) as the source address in outgoing probe
packets. On hosts with more than one IP address, this option can
be used to force the source address to be something other than
the IP address of the interface the probe packet is sent on. If
the IP address is not one of this machine's interface addresses,
an error is returned and nothing is sent.
Set the type-of-service in probe packets to the following value
(default zero). The value must be a decimal integer in the range
0 to 255. This option can be used to see if different types-of-
service result in different paths. (If you are not running a
4.3BSD-Tahoe or later system, this may be academic since the nor-
mal network services like telnet and ftp don't let you control
the TOS). Not all values of TOS are legal or meaningful - see the
IP spec for definitions. Useful values are probably `-t 16' (low
delay) and `-t 8' (high throughput).
Verbose output. Received ICMP packets other than TIME_EXCEEDED
and UNREACHABLEs are listed.
Set the time (in seconds) to wait for a response to a probe (de-
fault 3 sec.).
traceroute to nis.nsf.net (35.1.1.48), 30 hops max, 56 byte packet
1 helios.ee.lbl.gov (128.3.112.1) 19 ms 19 ms 0 ms
2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 39 ms 19 ms
4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 39 ms
5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 39 ms 39 ms 39 ms
6 128.32.197.4 (128.32.197.4) 40 ms 59 ms 59 ms
7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 59 ms
8 129.140.70.13 (129.140.70.13) 99 ms 99 ms 80 ms
9 129.140.71.6 (129.140.71.6) 139 ms 239 ms 319 ms
10 129.140.81.7 (129.140.81.7) 220 ms 199 ms 199 ms
11 nic.merit.edu (35.1.1.48) 239 ms 239 ms 239 ms
Ping will report duplicate and damaged packets. Duplicate packets should
never occur, and seem to be caused by inappropriate link-level retrans-
missions. Duplicates may occur in many situations and are rarely (if ev-
er) a good sign, although the presence of low levels of duplicates may
not always be cause for alarm.
traceroute to allspice.lcs.mit.edu (18.26.0.115), 30 hops max
1 helios.ee.lbl.gov (128.3.112.1) 0 ms 0 ms 0 ms
2 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 19 ms 19 ms
3 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 19 ms
4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 19 ms 39 ms 39 ms
5 ccn-nerif22.Berkeley.EDU (128.32.168.22) 20 ms 39 ms 39 ms
6 128.32.197.4 (128.32.197.4) 59 ms 119 ms 39 ms
7 131.119.2.5 (131.119.2.5) 59 ms 59 ms 39 ms
8 129.140.70.13 (129.140.70.13) 80 ms 79 ms 99 ms
9 129.140.71.6 (129.140.71.6) 139 ms 139 ms 159 ms
10 129.140.81.7 (129.140.81.7) 199 ms 180 ms 300 ms
11 129.140.72.17 (129.140.72.17) 300 ms 239 ms 239 ms
12 * * *
13 128.121.54.72 (128.121.54.72) 259 ms 499 ms 279 ms
14 * * *
15 * * *
16 * * *
17 * * *
18 ALLSPICE.LCS.MIT.EDU (18.26.0.115) 339 ms 279 ms 279 ms
2 lilac-dmc.Berkeley.EDU (128.32.216.1) 39 ms 19 ms 39 ms
3 lilac-dmc.Berkeley.EDU (128.32.216.1) 19 ms 39 ms 19 ms
4 ccngw-ner-cc.Berkeley.EDU (128.32.136.23) 39 ms 40 ms 19 ms
5 ccn-nerif35.Berkeley.EDU (128.32.168.35) 39 ms 39 ms 39 ms
6 csgw.Berkeley.EDU (128.32.133.254) 39 ms 59 ms 39 ms
7 * * *
8 * * *
9 * * *
10 * * *
11 * * *
12 * * *
13 rip.Berkeley.EDU (128.32.131.22) 59 ms ! 39 ms ! 39 ms !