Jenkins version 2.62

Jenkins master + Jenkins slave Ubuntu 16.04 instances

Jenkins jnlp slave fails with an error:

java.io.IOException: Failed to connect to 185.109.149.152:37736
at org.jenkinsci.remoting.engine.JnlpAgentEndpoint.open(JnlpAgentEndpoint.java:243)
at hudson.remoting.Engine.connect(Engine.java:500)
at hudson.remoting.Engine.innerRun(Engine.java:364)
at hudson.remoting.Engine.run(Engine.java:287)
Caused by: java.net.ConnectException: Connection refused
at sun.nio.ch.Net.connect0(Native Method)
at sun.nio.ch.Net.connect(Net.java:454)
at sun.nio.ch.Net.connect(Net.java:446)
at sun.nio.ch.SocketChannelImpl.connect(SocketChannelImpl.java:648)
at java.nio.channels.SocketChannel.open(SocketChannel.java:189)
at org.jenkinsci.remoting.engine.JnlpAgentEndpoint.open(JnlpAgentEndpoint.java:204)
... 3 more

I have played around with the ipv6 settings (disabled)

with random/fixed JNLP port (37736)

I see that the port is in LISTEN mode:

root@192-168-10-6:~# netstat -plunt | grep java
tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN 1954/java
tcp 0 0 0.0.0.0:4444 0.0.0.0:* LISTEN 1981/java
tcp 0 0 0.0.0.0:37736 0.0.0.0:* LISTEN 1954/java
udp 0 0 0.0.0.0:33848 0.0.0.0:* 1954/java
udp 0 0 0.0.0.0:5353 0.0.0.0:* 1954/java

BUT, connection is not established.

telnet from the slave instance doesn't work

all firewall rules are open (between the slave and the master)