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.
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
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.
-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.
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.
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.
The ping command appeared in 4.3BSD.
The version described here is its descendant specific to Linux.
ping requires CAP_NET_RAWIO capability to be executed. It may be used as set-uid root.
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.
The Story of the PING Program
Source code of PING: