omping (8) - Linux Manuals

omping: test IP multicast


omping - test IP multicast


[-46CDEFqVv [-c count ] ] [-i interval ] [-M transport_method ] [-m mcast_addr ] [-O op_mode ] [-p port ] [-R rcvbuf ] [-r rate_limit ] [-S sndbuf ] [-T timeout ] [-t ttl ] [-w wait_time ] remote_addr...


The is program which uses User Datagram Protocol to determine if computer is able to send and/or receive IP unicast and multicast or Broadcast packets from the network. It's designed to be used in very similar way as ping(8) and also has some features of the fping(8) command. Where ping(8) and differ is in who replies. In ping(8) replies are sent by the operating system and with another instance of sends the reply. This mean that must be running on all computers to test sending/receiving IP multicast/broadcast. Its arguments are as follows:

Force usage of IPv4.
Force usage of IPv6.
Display continuous statistics for every reply message.
Disable packet duplicate detection. Option is default for interval 0.
Default behaviour when every client is in stop state is to exit. This may happen if all server sends stop message or if count query messages was sent. This option changes default behaviour and doesn't quit automatically.
Allow entering of arguments which are not allowed or not recommended by the specification. This is typically the interval parameter. This option may be used multiple times.
Quiet output. Nothing is displayed except state changes and summary. Option can be used twice and then only summary is displayed.
Display version and quit. Option can be used twice and then remote version is displayed.
Set level of verbosity. Parameter can be used multiple times to achieve higher verbosity.
-c count
Number of request packets to send to each target. After sending count query messages, given client is put to stop state and it is no longer sending query messages.
-i interval
Wait interval seconds between sending each request packet. Float values are supported in millisecond precision. It's possible to set there 0 with meaning that packets are sent ether after previous unicast reply is received or after 1 millisecond, depending on which of these intervals is smaller. The default is to wait for one second between each packet.
-M transport_method
Set transport method to use. This can be asm for Any-source Multicast, ssm for Source-specific Multicast and ipbc for IP Broadcast.
-m mcast_addr
Multicast or broadcast address to listen on for multicast/broadcast answer messages. Default is for IPv4 and ff3e::4321:1234 for IPv6 multicast, or broadcast address of local interface for Broadcast.
-O op_mode
can be running in three different modes. Default and recommended mode for quick testing is normal mode, when behaves like client and server together. It sends queries and is able to respond them. Finally the client mode sends queries, but never respond to other nodes.
-p port
Port to bind and listen on for both unicast and multicast/broadcast messages. Default is 4321.
-R rcvbuf
Set socket rcvbuf. Minimum value for this option is 2048. If not specified, rcvbuf is not changed and default OS provided value is used.
-r rate_limit
Rate limit interval between two query messages to rate_limit seconds. Default value is same as interval given by -i option. Rate limiting can be disabled by specifying 0 as value. Rate limiting is by default disabled for -i with 0 seconds.
-S sndbuf
Set socket sndbuf. Minimum value for this option is 2048. If not specified, sndbuf is not changed and default OS provided value is used.
-T timeout
Specify a timeout, in seconds, before exits regardless of how many packets have been received.
-t ttl
Time-To-Live of sent packets.
-w wait_time
after is stopped (by sending SIGINT or timeout expire) it is moved to special state when no queries are made and server answer all queries by server response (stop message). This makes possible to give correct (unbiased) result of lost packets on other nodes. Default is 3 times interval or 1 second, depending which one is larger. Also special value 0 can be used to not wait at all or -1 which means wait forever (this can be still terminated by sending SIGINT).
List of addresses to test. One of them must be address of local internet interface. This local address is used for bind and listening on for unicast packets. It's also used to determine which interface should be used for sending multicast/broadcast replies.

Program is normally terminated by SIGINT. After signal receive summary is displayed. You can also display summary during running by sending SIGINFO or SIGUSR1 signal.

When using for fault isolation, it should first be run against local internet interface only, to verify that the local network interface is up and running, and firewall is correctly configured. This mode is available by entering only local IP address.


Ex -std


The following commands and output is a typical way how to find-out and solve network problems using omping. In this situation, we have 3 computers named node-01, node-02 and node-03 with IP addresses - Let's run the following command on all of them.

$ omping node-01 node-02 node-03

on all of nodes we should be able to seen similar output

node-01 : waiting for response msg
node-03 : waiting for response msg
node-01 : joined (S,G) = (*,, pinging
node-03 : joined (S,G) = (*,, pinging
node-01 : unicast, seq=1, size=69 bytes, dist=0, time=0.192ms
node-01 : multicast, seq=1, size=69 bytes, dist=0, time=0.284ms
node-03 : unicast, seq=1, size=69 bytes, dist=0, time=0.279ms
node-03 : multicast, seq=1, size=69 bytes, dist=0, time=0.360ms

The first two lines tell us, that node-02 (actual node) is waiting for a response message from node-01 and node-03. The second two lines contain information, that we were successfully able to send an init message and also received a response message from remote nodes. Both of these messages are unicast, so we are able to send and receive unicast messages on a given port. If all of nodes are up and is running on all of them, but we are not able to receive a response message, it's time to check connectivity between nodes. First make sure that you are able to ping(8) them. If so, make sure that your firewall allows port 4321 to receive udp packets.

The next line tells us that we were able to receive a 69 byte unicast response message from node-01, with a sequence number of 1. The distance between the computers is 0 so they are on the same link net. Time between send and receive packet was 0.192 ms, that is also the current average time and lastly there were no lost packets.

The 6th line tells us the same information as the previous one, but the received message is a multicast message. It means, that multicast is probably well configured.

The 7th and 8th lines are same as previous two one but for node-03.

If the node is able to receive unicast packets, but never multicast, it means that multicast configuration is incorrect. It's recommended to turn off your firewall. If multicast packets start to arrive, great. If not, the problem is hidden in the switches/routers between the nodes. Contact your system administrator to allow multicast traffic on the switch or router.

is terminated by SIGINT signal (CTRL-c). Summary statistics are shown

node-01 : unicast, xmt/rcv/%loss = 18/18/0%, min/avg/max/std-dev = 0.177/0.301/0.463/0.073
node-01 : multicast, xmt/rcv/%loss = 18/18/0%, min/avg/max/std-dev = 0.193/0.335/0.547/0.090
node-03 : unicast, xmt/rcv/%loss = 21/21/0%, min/avg/max/std-dev = 0.272/0.299/0.327/0.017
node-03 : multicast, xmt/rcv/%loss = 21/20/4% (seq>=2 0%), min/avg/max/std-dev = 0.347/0.388/0.575/0.055

Last line has additional information (seq>=2 %0) which means, that after receiving first multicast packet with seq number 2, no other multicast packet was lost. Because creating multicast tree is time consuming, it's pretty normal to lost first few multicast packets. rcv field can also be formatted like

node-01 : unicast, xmt/rcv/%loss = 3/3+1/0%, min/avg/max/std-dev = 0.294/0.299/0.305/0.006

This means, that 1 duplicate packet was received. It's possible to find out duplicate packet by looking to output and find line which has following format

node-01 : unicast, seq=2 (dup), size=69 bytes, dist=0, time=0.469ms


uses Internet-Draft draft-ietf-mboned-ssmping-08 as underlaying protocol and tries to be as compliant as possible.


The utility was written by An Jan Friesse Aq jfriesse [at] .


Some OSes may not have support for receiving TTL from packet.
then cannot provide distance information.
Some OSes may not provide information about packet receive. Less precise actual time is then used.
highly depends on precise poll(2) and gettimeofday(3) functions. If OS doesn't provide at least milliseconds precision, results may be incorrect.


fping(8), ping(8)