2ping - Man Page

A bi-directional ping utility


2ping [options] --listen | host/IP [host/IP [...]]


2ping is a bi-directional ping utility. It uses 3-way pings (akin to TCP SYN, SYN/ACK, ACK) and after-the-fact state comparison between a 2ping listener and a 2ping client to determine which direction packet loss occurs.

To use 2ping, start a listener on a known stable network host. The relative network stability of the 2ping listener host should not be in question, because while 2ping can determine whether packet loss is occurring inbound or outbound relative to an endpoint, that will not help you determine the cause if both of the endpoints are in question.

Once the listener is started, start 2ping in client mode and tell it to connect to the listener. The ends will begin pinging each other and displaying network statistics. If packet loss occurs, 2ping will wait a few seconds (default 10, configurable with --inquire-wait) before comparing notes between the two endpoints to determine which direction the packet loss is occurring.

To quit 2ping on the client or listener ends, enter ^C, and a list of statistics will be displayed. To get a short inline display of statistics without quitting, enter ^\ or send the process a QUIT signal.


ping-compatible options (long option names are 2ping-specific):

--audible,  -a

Audible ping.

--adaptive,  -A

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

--count=count, -c count

Stop after sending count ping requests.

--flood,  -f

Flood ping. For every ping sent a period “.” is printed, while for ever ping received a backspace is printed. This provides a rapid display of how many pings are being dropped. If interval is not given, it sets interval to zero and outputs pings as fast as they come back or one hundred times per second, whichever is more.

2ping-specific notes: Detected outbound/inbound loss responses are printed as “>” and “<”, respectively. Receive errors are printed as “E”. Due to the asynchronous nature of 2ping, successful responses (backspaces) may overwrite these loss and error characters.

--interval=interval, -i interval

Wait interval seconds between sending each ping. The default is to wait for one second between each ping normally, or not to wait in flood mode.

--interface-address=address, -I address

Set source IP address. When in listener mode, this option may be specified multiple to bind to multiple IP addresses. When in client mode, this option may only be specified once, and all outbound pings will be bound to this source IP.

2ping-specific notes: This option only takes an IP address, not a device name. Note that in listener mode, if the machine has an interface with multiple IP addresses and an request comes in via a sub IP, the reply still leaves via the interface’s main IP. So either this option – or (preferred) listening on all IPs individually via the Python “netifaces” module – must be used if you would like to respond via an interface’s sub-IP.

--preload=count, -l count

If specified, 2ping sends that many packets not waiting for reply.

--pattern=hex_bytes, -p hex_bytes

You may specify up to 16 “pad” bytes to fill out the packets you send. This is useful for diagnosing data-dependent problems in a network. For example, --pattern=ff will cause the sent packet pad area to be filled with all ones.

2ping-specific notes: This pads the portion of the packet that does not contain the active payload data. If the active payload data is larger than the minimum packet size (--min-packet-size), no padding will be sent.

--quiet,  -q

Quiet output. Nothing is displayed except the summary lines at startup time and when finished.

--packetsize-compat=bytes, -s bytes

ping compatibility; this will set --min-packet-size to this plus 8 bytes.

--verbose,  -v

Verbose output. In 2ping, this prints decodes of packets that are sent and received.

--version,  -V

Show version and exit.

--deadline=seconds, -w seconds

Specify a timeout, in seconds, before 2ping exits regardless of how many pings have been sent or received. Due to blocking, this may occur up to one second after the deadline specified.

2ping-specific options:

--help,  -h

Print a synposis and exit.

--ipv4,  -4

Limit binds to IPv4. In client mode, this forces resolution of dual-homed hostnames to the IPv4 address. (Without --ipv4 or --ipv6, the first result will be used as specified by your operating system, usually the AAAA address on IPv6-routable machines, or the A address on IPv4-only machines.) In listener mode, this filters out any non-IPv4 --interface-address binds, either through hostname resolution or explicit passing.

--ipv6,  -6

Limit binds to IPv6. In client mode, this forces resolution of dual-homed hostnames to the IPv6 address. (Without -4 or -6, the first result will be used as specified by your operating system, usually the AAAA address on IPv6-routable machines, or the A address on IPv4-only machines.) In listener mode, this filters out any non-IPv6 --interface-address binds, either through hostname resolution or explicit passing.


Deprecated. In listener mode, all addresses will be listened to by default if the Python “netifaces” module is installed, unless overridden by one or more --interface-address invocations.


Set a shared key, send cryptographic hashes with each packet, and require cryptographic hashes from peer packets signed with the same shared key.


When --auth is used, specify the digest type to compute the cryptographic hash. Valid options are hmac-md5 (default), hmac-sha1, hmac-sha256 and hmac-sha512.


Print (lots of) debugging information.


Set a shared key, encrypt 2ping packets, and require encrypted packets from peers encrypted with the same shared key. Requires the PyCryptodome or PyCrypto module.


When --encrypt is used, specify the method used to encrypt packets. Valid options are hkdf-aes256-cbc (default).


Simulate corruption of incoming packets, with a percent probability each bit will be flipped. After fuzzing, the packet checksum will be recalculated, and then the checksum itself will be fuzzed (but at a lower probability).


Wait at least secs seconds before inquiring about a lost packet. Default is 10 seconds. UDP packets can arrive delayed or out of order, so it is best to give it some time before inquiring about a lost packet.


Start as a listener. The listener will not send out ping requests at regular intervals, and will instead wait for the far end to initiate ping requests. A listener is required as the remote end for a client. When run as a listener, a SIGHUP will reload the configuration on all interfaces.


Use one or more client/listener pairs of UNIX datagram sockets. Mainly for testing purposes.


Number of pairs to generate when using --loopback.


Set the minimum total payload size to min bytes, default 128. If the payload is smaller than min bytes, padding will be added to the end of the packet.


Set the maximum total payload size to max bytes, default 512, absolute minimum 64. If the payload is larger than max bytes, information will be rearranged and sent in future packets when possible.


Produce output suitable for use in a Nagios check. If --count is not specified, defaults to 5 pings. A warning condition (exit code 1) will be returned if average RTT exceeds wrta or ping loss exceeds wloss%. A critical condition (exit code 2) will be returned if average RTT exceeds crta or ping loss exceeds closs%.


Do not perform 3-way pings. Used most often when combined with --listen, as the listener is usually the one to determine whether a ping reply should become a 3-way ping.

Strictly speaking, a 3-way ping is not necessary for determining directional packet loss between the client and the listener. However, the extra leg of the 3-way ping allows for extra chances to determine packet loss more efficiently. Also, with 3-way ping disabled, the listener will receive no client performance indicators, nor will the listener be able to determine directional packet loss that it detects.


When sending replies, 2ping will try to match the packet size of the received packet by adding padding if necessary, but will not exceed --max-packet-size. --no-match-packet-size disables this behavior, always setting the minimum to --min-packet-size.


Do not send the current running version of 2ping with each packet.


Send arbitrary notice text with each packet. If the remote peer supports it, this may be displayed to the user.


Simulate random packet loss outbound and inbound. For example, 25:10 means a 25% chance of not sending a packet, and a 10% chance of ignoring a received packet. A single number without colon separation means use the same percentage for both outbound and inbound.


Use UDP port port, either a numeric port number or a service name string. With --listen, this is the port to bind as, otherwise this is the port to send to. Default is UDP port 15998.

When port “-1” is specified, a random unused high port is picked. This is useful for automated unit and functional testing, but not for normal use.


Send a monotonic clock value with each packet. Peer time (if sent by the peer) can be viewed with --verbose.


Send random data to the peer, up to bytes. The number of bytes will be limited by other factors, up to --max-packet-size. If this data is to be used for trusted purposes, it should be combined with --auth for HMAC authentication.


Send the host time (wall clock) with each packet. Peer time (if sent by the peer) can be viewed with --verbose.


In client mode, causes hostnames to be looked up via DNS SRV records. If the SRV query returns multiple record targets, they will all be pinged in parallel; priority and weight are not considered. The record’s port will be used instead of --port. This functionality requires the dnspython module to be installed.


When combined with --srv, service name to be used for SRV lookups. Default service is “2ping”.


Print a line of brief current statistics every interval seconds. The same line can be printed on demand by entering ^\ or sending the QUIT signal to the 2ping process.


If a peer sends its host latency (the amount of time it spends between receiving a packet and sending out a reply), subtract it from RTT calculations.


None known, many assumed.


2ping was written by Ryan Finnie <ryan@finnie.org>.


Ryan Finnie.

Referenced By

The man page 2ping6(1) is an alias of 2ping(1).