Can it be ROS master is dropping remote connections [closed]
Hi, I have RPi (Raspbian 9/kinetic) and a PC (bionic/melodic). They are connected directly via an Ethernet cable and dnsmasq. I would guess that there is no firewal, because (pi$ is the command line on Pi, pc$ is the command line on the pc)
pi$ netcat -l 11311
pc$ netcat pi 11311
works fine, and in the opposite direction
pc$ netcat -l 11311
pi$ netcat pi 11311
the two ends can talk one to another as well. Also, they say that there is no firewall by default in Raspbian9 and Ubuntu19, but I removed ufw just to be sure. Now when I run the master on pi, I can talk with it locally:
pi$ netcat localhost 11311
q
<head>
<title>Error response</title>
</head>
<body>
<h1>Error response</h1>
<p>Error code 400.
<p>Message: Bad request syntax ('q').
<p>Error code explanation: 400 = Bad request syntax or unsupported method.
</body>
But the same on the pc just exits:
pc$ netcat pi 11311
pc$
I know that it looks like a firewall, but why netcat can talk with itself via 11311 in both directions on the same machines?
Here is my .bashrc on pi:
export ROS_HOSTNAME=localhost
export ROS_MASTER_URI=http://$ROS_HOSTNAME:11311
source /opt/ros/kinetic/setup.bash
source ~/catkin_ws/devel/setup.bash
and here on the pc:
export ROS_IP=10.42.0.216
export ROS_HOSTNAME=pi
export ROS_MASTER_URI=http://$ROS_HOSTNAME:11311
source /opt/ros/melodic/setup.bash
source ~/catkin_ws/devel/setup.bash
ROS_IP is the IP of pi in /etc/hosts:
127.0.0.1 localhost
127.0.1.1 art
10.42.0.216 pi
I just added it to be sure. This works fine as well:
pc$ ssh pi@pi
pi$ ssh art@rosmaster
iptables on both systems:
pi# iptables -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
I wonder if ROS master drops remote connections for whatever purpose? If not, do you have any idea what a problem can it be? dnsmasq? An incompatibility between kinetic/bionic, whatever? But kinetic on Pi does not ask for anything, in particular it does not ask about the version of the other distribution.
Did you try
I tried the same with pi instead of pi.local, as seen in .bashrc in the question; avahi sets pi as raspberrypi.local and tried it as well
also, netcat, a low-level tool, sees nothing listening on both pi:11311 and raspberrypi.local:11311; it sees, however, the ports themselves as there is no "name or service not known" error; and it can talk fine if there is also netcat on the pi side instead of roscore