Port not responding remotely, but shows as open locally

Question

UPDATE:

I opened a ticket with DO and was informed that they'd automatically closed port 8083 due to the VestaCP vulnerability which allowed root access to droplets. While I'm happy that I found out what was causing my problem, I'm disappointed in DO that they did not contact their users to inform them about this. Multiple hours were wasted on this problem, hours that I won't get back.

On my DO server, I have bound my API to port 8083, and it was working normally until today. Now whenever I try to connect to my API, the connection times out. I tried to connect to that port using nc -zv host port but it hangs up as well.

Strangely, changing the port in my API, recompiling it and running it works perfectly. Almost all other ports work, except 8083.

I sshd into the box, and ran nc -zv localhost 8083 and got a connection successful message. I don't think I have any firewall blocking it, because I ran service iptables status and it says iptables.service not running.

So, now I have two options, either use a different port for my API (which is troublesome, as the port is hardcoded into the Android app I use the API for), or figure this out.

Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name

tcp        0      0 0.0.0.0:2222            0.0.0.0:*               LISTEN      1328/sshd
tcp6       0      0 :::8086                 :::*                    LISTEN      1586/api1
tcp6       0      0 :::3306                 :::*                    LISTEN      1343/mysqld
tcp6       0      0 :::2222                 :::*                    LISTEN      1328/sshd
tcp6       0      0 :::8080                 :::*                    LISTEN      1583/api2
tcp6       0      0 :::8082                 :::*                    LISTEN      1574/api3
tcp6       0      0 :::8083                 :::*                    LISTEN      1801/api4
tcp6       0      0 :::8084                 :::*                    LISTEN      1571/api5
tcp6       0      0 :::8085                 :::*                    LISTEN      1577/api6

What could be the problem.

TheCompWiz · Answer

There are a large number of reasons a service bound to a tcp port would not accept a connection. Perhaps within the application there is an ACL that only accepts connections from a specific IP. Perhaps the service requires a gate-keeper connection to initially begin some sort of session before other connections are accepted on that port. Perhaps it is a service that only allows a limited number of connections and it is full. Perhaps iptables is blocking or filtering connections. ... the list goes on.

Perhaps you should look at what process has the port bound by looking at netstat -an -p to figure out the PID, and look into what the process is.

Perhaps you should look at what process has the port bound by looking at netstat -an -p to figure out the PID, and look into what the process is.

Port not responding remotely, but shows as open locally

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