Problems with blocked/not responding ports

[randaz81]

This QA applies to the following cases:

• yarpmotorgui hangs up during startup, in particular while trying to open /robot/part/xxxx port.
• yarp read ... /port does not display anything on machine A, but it works correctly if executed on the machine B.

[randaz81]

There are two typical causes:

• A firewall is set on machine A. Especially if your machine is a windows machine check the configuration of your firewall.
• The yarp server is misconfigured. If yarp server has been launched on a machine with multiple ethernet boards, check that it is using the correct address (by default yarp server will choose the first available one).

Consider the following example:

On a robot, the control pc (e.g. pc104) has one internal board (ip: 10.0.1.104) and one external board (ip: 192.168.100.10). The board with 10.0.1.104 is intended to communicate with the robot internal boards. The yarp server, instead, has to be configured to run on the external board with ip address 192.168.100.10. This is accomplished using the command:
yarp conf 10.0.0.10 10000
NB: if yarp server is started using port 10.0.1.104, you may experience exactly the problems of mono-directional communication described above.

Moreover:

If you start yarp server and it fails to launch, displaying a message similar to:

    __  __ ___  ____   ____
    \ \/ //   ||  _ \ |  _ \
     \  // /| || |/ / | |/ /
     / // ___ ||  _ \ |  _/
    /_//_/  |_||_| \_\|_|
    ========================

Call with --help for information on available options
Using port database: :memory:
Using subscription database: :memory:
IP address: default
Port number: 10000
Overriding loopback address for name server
PROBLEM: need to change settings in /home/r1-user/.config/yarp/_cer01.conf
  Current settings: host 192.168.100.10 port 10000 family yarp
  Desired settings:  host 10.0.1.104 port 10000 family yarp
Please specify '--write' if it is ok to overwrite current settings, or
Please specify '--read' to use the current settings, or
delete /home/r1-user/.config/yarp/_cer01.conf
Aborting.

you are warned that you are not using the usual configuration and there exists the possibility that you are doing something wrong (e.g. requesting to run yarp server on the wrong ethernet board 10.0.1.104). Yarp server will seem to run correctly both if you execute it with --write and --read option so read carefully the ip addresses of the two interfaces displayed in the message and choose the right one, otherwise other machines of cluster will be not able to receive data through yarp ports. In this specific example use command yarpserver --read to use the correct settings.