Ping

ping .. pong

ping    [from the submariners' term for a sonar pulse]

1. n. Slang term for a small network message (ICMP ECHO) sent by a computer to check for the presence and alertness of another. The Unix command ping(8) can be used to do this manually (note that ping(8)'s author denies the widespread folk etymology that the name was ever intended as acronym for `Packet INternet Groper'). Occasionally used as a phone greeting. See ACK, also ENQ.

2. vt. To verify the presence of.

3. vt. To get the attention of.

4. vt. To send a message to all members of a mailing list requesting an ACK (in order to verify that everybody's addresses are reachable). "We haven't heard much of anything from Geoff, but he did respond with an ACK both times I pinged jargon-friends."

5. n. A quantum packet of happiness. People who are very happy tend to exude pings; furthermore, one can intentionally create pings and aim them at a needy party (e.g., a depressed person). This sense of ping may appear as an exclamation; "Ping!" (I'm happy; I am emitting a quantum of happiness; I have been struck by a quantum of happiness). The form "pingfulness", which is used to describe people who exude pings, also occurs. (In the standard abuse of language, "pingfulness" can also be used as an exclamation, in which case it's a much stronger exclamation than just "ping"!). Oppose blargh.

PingStorm

man ping

SYNOPSIS ping [ -LRUbdfnqrvVaA]  [ -c count]  [ -i interval]  [ -l preload] [ -p pattern]  [ -s packetsize]  [ -t ttl]  [ -w deadline] [ -F flowlabel]  [ -I interface]  [ -M hint]  [ -Q tos] [ -S sndbuf]  [ -T timestamp option]  [ hop  ...] destination

DESCRIPTION ping uses the ICMP protocol's mandatory ECHO_REQUEST data- gram to elicit an ICMP ECHO_RESPONSE from a host or gate- way. 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.

OPTIONS -a    Audible ping.

-A    Adaptive  ping. Interpacket interval  adapts   to              round-trip  time, so that effectively not more than one (or more, if preload is set) unanswered probes present in the network. Minimal interval is 200msec for not super-user. On networks with low rtt this mode is essentially equivalent to flood mode.

-b    Allow pinging a broadcast address.

-c count Stop after sending count ECHO_REQUEST packets. With deadline option, ping waits for  count  ECHO_REPLY packets, until the timeout expires.

-d    Set  the  SO_DEBUG option on the socket being used. Essentially, this socket option  is  not  used  by              Linux kernel.

-F flow label Allocate and set 20 bit flow label on echo request packets. (Only ping6). If value is  zero,  kernel allocates random flow label.

-f    Flood  ping. 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. If interval is not given, it sets inter- val to zero and outputs packets as  fast  as  they come  back   or  one  hundred  times  per  second, whichever is more. Only the  super-user  may  use this option with zero interval.

If preload is specified, ping sends that many pack- ets not waiting for reply. Only the super-user may select preload more than 3.

-L    Suppress loopback of multicast packets. This flag only applies if the ping destination is a multicast address.

-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 tos Set Quality of Service -related bits in ICMP data- grams. tos can be either decimal or  hex  number. Traditionally (RFC1349),  these  have  been inter- preted as: 0 for reserved (currently  being  rede-              fined  as congestion control), 1-4 for Type of Ser- vice and 5-7 for Precedence. Possible settings for Type of Service are: minimal cost: 0x02, reliabil- ity: 0x04, throughput: 0x08, low delay: 0x10. Mul- tiple TOS  bits  should not be set simultaneously. Possible settings for special Precedence range from priority (0x20) to net control (0xe0). You must be             root (CAP_NET_ADMIN capability) to use Critical  or              higher  precedence  value. You cannot set bit 0x01 (reserved) unless ECN has been enabled in the ker- nel. In RFC2474, these fields has been redefined as 8-bit Differentiated Services (DS),  consisting of: bits  0-1  of separate data (ECN will be used,              here), and  bits  2-7  of  Differentiated  Services Codepoint (DSCP).

-q    Quiet output. Nothing is displayed except the sum- mary lines at startup time and when finished.

-R    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 interface. 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

-T timestamp option Set special IP timestamp options. timestamp option may be either tsonly (only timestamps),  tsandaddr (timestamps  and  addresses)  or  tsprespec  host1 [host2 [host3  [host4]]]  (timestamp  prespecified              hops).

-M hint Select Path  MTU  Discovery strategy. hint may be             either do (prohibit fragmentation, even local one), want (do  PMTU  discovery,  fragment  locally when              packet size is large),  or  dont  (do  not  set  DF              flag).

-U    Print    full   user-to-user   latency   (the   old              behaviour). Normally ping prints network round trip time, which can be different f.e. due to DNS fail- ures.

-v    Verbose output.

-V    Show version and exit.

-w deadline Specify a timeout, in seconds, before  ping  exits regardless of  how  many packets have been sent or              received. In this case ping does  not  stop  after count packet are sent, it waits either for deadline expire or until count probes are answered  or  for some error notification from network.

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 fur- ther and further away should  be  ``pinged''. Round-trip times and packet loss statistics are computed. If dupli- cate packets are received, they are not included  in  the packet loss  calculation, although the round trip time of       these packets is used  in  calculating  the  minimum/aver- age/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. Shorter current  statistics  can  be  obtained without termination of process with signal SIGQUIT.

If ping does not receive any reply packets at all it will exit with code 1. If a packet count and deadline are both specified, and  fewer  than count packets are received by       the time the deadline has arrived, it will also exit  with code 1. On other error it exits with code 2. Otherwise it      exits with code 0. This makes it possible to use the exit code to see if a host is alive or not. requested data space (the ICMP header).

If the  data  space is at least of size of struct timeval ping uses the beginning bytes of this space to include  a       timestamp  which  it uses in the computation of round trip times. If the data space is shorter, no round trip times are given.

DUPLICATE AND DAMAGED PACKETS ping 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 ping packet's path (in the network or in the hosts).

TRYING DIFFERENT DATA PATTERNS 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  pat- tern 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 pat- tern 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.

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 TTL value of an IP packet represents the maximum num- ber 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 value in the received packet will be 255 minus the num- ber of routers in the round-trip path.

o 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 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 o Many Hosts and Gateways ignore the RECORD_ROUTE option.

o 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.

o Flood pinging is not recommended in general, and  flood pinging the broadcast address should only be done under very controlled conditions.

SEE ALSO netstat(1), ifconfig(8).

HISTORY The ping command appeared in 4.3BSD.

The version described here is its descendant specific  to       Linux.

SECURITY ping requires CAP_NET_RAWIO capability to be executed. It      may be used as set-uid root.

AVAILABILITY ping is part of iputils package and the  latest  versions are   available   in   source   form  for  anonymous  ftp ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz.

>=== External Links ===

The Story of the PING Program
 * http://ftp.arl.mil/~mike/ping.html

Source code of PING:
 * ftp://ftp.arl.army.mil/pub/ping.shar



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