4.3BSD-Reno/share/man/cat8/ping.0
PING(8) 1990 PING(8)
NNAAMMEE
ping - send ICMP ECHO_REQUEST packets to network hosts
SSYYNNOOPPSSIISS
ppiinngg [ --ddffnnqqrrvvRR ][ --cc count][ --ii wait][ --ll preload][ --pp pat-
tern][ --ss packetsize]
DDEESSCCRRIIPPTTIIOONN
_P_i_n_g 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 _s_t_r_u_c_t _t_i_m_e_v_a_l and then an arbi-
trary number of ``pad'' bytes used to fill out the packet.
The options are as follows: Other options are:
-_c _c_o_u_n_t
Stop after sending (and receiving) _c_o_u_n_t ECHO_RESPONSE
packets.
-_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 ECHO_REQUEST sent a period ``.'' is printed,
while for ever ECHO_REPLY 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. _T_h_i_s _c_a_n _b_e _v_e_r_y _h_a_r_d _o_n _a _n_e_t_w_o_r_k _a_n_d
_s_h_o_u_l_d _b_e _u_s_e_d _w_i_t_h _c_a_u_t_i_o_n.
-_i _w_a_i_t
Wait _w_a_i_t _s_e_c_o_n_d_s _b_e_t_w_e_e_n _s_e_n_d_i_n_g _e_a_c_h _p_a_c_k_e_t. The
default is to wait for one second between each packet.
This option is incompatible with the -_f option.
-_l _p_r_e_l_o_a_d
If _p_r_e_l_o_a_d is specified, _p_i_n_g sends that many packets
as fast as possible before falling into its normal mode
of behavior.
-_n Numeric output only. No attempt will be made to lookup
symbolic names for host addresses.
-_p _p_a_t_t_e_r_n
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 output. Nothing is displayed except the summary
lines at startup time and when finished.
Printed 7/27/90 June 1
PING(8) 1990 PING(8)
--RR Record route. Includes the RECORD_ROUTE option in the
ECHO_REQUEST packet and displays the route buffer on
returned packets. Note that the IP header is only
large enough for nine such routes. 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 _r_o_u_t_e_d(8)).
-_s _p_a_c_k_e_t_s_i_z_e
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.
-_v Verbose output. ICMP packets other than ECHO_RESPONSE
that are received are listed.
When using _p_i_n_g for fault isolation, it should first be run
on the local host, to verify that the local network inter-
face 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 cal-
culation, although the round trip time of these packets is
used in calculating the minimum/average/maximum round-trip
time numbers. When the specified number of packets have
been sent (and received) or if the program is terminated
with a SIGINT, a brief summary is displayed.
This program is intended for use in network testing, meas-
urement and management. Because of the load it can impose
on the network, it is unwise to use _p_i_n_g during normal
operations or from automated scripts.
IICCMMPP PPAACCKKEETT DDEETTAAIILLSS
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 arbitrary amount of data. When a
_p_a_c_k_e_t_s_i_z_e 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).
If the data space is at least eight bytes large, _p_i_n_g 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
Printed 7/27/90 June 2
PING(8) 1990 PING(8)
times are given.
DDUUPPLLIICCAATTEE AANNDD DDAAMMAAGGEEDD PPAACCKKEETTSS
_P_i_n_g will report duplicate and damaged packets. Duplicate
packets should never occur, and seem to be caused by inap-
propriate link-level retransmissions. Duplicates may occur
in many situations and are rarely (if ever) a good sign,
although the presence of low levels of duplicates may not
always be cause for alarm.
Damaged packets are obviously serious cause for alarm and
often indicate broken hardware somewhere in the _p_i_n_g
packet's path (in the network or in the hosts).
TTRRYYIINNGG DDIIFFFFEERREENNTT DDAATTAA PPAATTTTEERRNNSS
The (inter)network layer should never treat packets dif-
ferently depending on the data contained in the data por-
tion. 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 relation-
ship between what you type and what the controllers transmit
can be complicated.
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 _p_i_n_g.
TTTTLL DDEETTAAIILLSS
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.
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 _t_e_l_n_e_t or _f_t_p.
Printed 7/27/90 June 3
PING(8) 1990 PING(8)
In normal operation ping prints the ttl value from the
packet it receives. When a remote system receives a ping
packet, it can do one of three things with the TTL field in
its response:
-- 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.
-- Set it to 255; this is what current Berkeley Unix sys-
tems do. In this case the TTL value in the received
packet will be 255 minus the number of routers in the
path _f_r_o_m the remote system _t_o the _p_i_n_ging host.
-- 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.
BBUUGGSS
Many Hosts and Gateways ignore the RECORD_ROUTE option.
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 ping-
ing the broadcast address should only be done under very
controlled conditions.
SSEEEE AALLSSOO
netstat(1), ifconfig(8), routed(8)
Printed 7/27/90 June 4