What can be the reasons of connection refused errors

Question

I m trying to write a server program in C   using another client  I get this error when I try to connect through port 2080 for example   connection refused   What can be the reasons of this error

User · Answer

I had the same message with a totally different cause: the wsock32.dll was not found. The ::socket(PF_INET, SOCK_STREAM, 0); call kept returning an INVALID_SOCKET but the reason was that the winsock dll was not loaded.

In the end I launched Sysinternals' process monitor and noticed that it searched for the dll 'everywhere' but didn't find it.

Silent failures are great!

User · Answer

There could be many reasons  but the most common are    The port is not open on the destination machine  The port is open on the destination machine  but its backlog of pending connections is full  A firewall between the client and server is blocking access  also check local firewalls     After checking for firewalls and that the port is open  use telnet to connect to the ip port to test connectivity  This removes any potential issues from your application

User · Answer

Although it does not seem to be the case for your situation  sometimes a connection refused error can also indicate that there is an ip address conflict on your network   You can search for possible ip conflicts by running    arp-scan -I eth0 -l   grep  lt ipaddress gt    and   arping  lt ipaddress gt    This AskUbuntu question has some more information also

User · Answer

If you try to open a TCP connection to another host and see the error  Connection refused   it means that   You sent a TCP SYN packet to the other host  Then you received a TCP RST packet in reply     RST is a bit on the TCP packet which indicates that the connection should be reset  Usually it means that the other host has received your connection attempt and is actively refusing your TCP connection  but sometimes an intervening firewall may block your TCP SYN packet and send a TCP RST back to you   See https   tools ietf org html rfc793 page 69      SYN-RECEIVED STATE      If the RST bit is set      If this connection was initiated with a passive OPEN  i e    came   from the LISTEN state   then return this connection to  LISTEN state   and return   The user need not be informed   If  this connection was   initiated with an active OPEN  i e   came  from SYN-SENT state  then   the connection was refused  signal  the user  connection refused    In   either case  all segments  on the retransmission queue should be   removed   And in the  active OPEN case  enter the CLOSED state and   delete the TCB   and return

User · Answer

In my case  it happens when the site is blocked in my country and I don t use VPN  For example when I try to access vimeo com from Indonesia which is blocked

User · Answer

Check at the server side that it is listening at the port 2080  First try to confirm it on the server machine by issuing telnet to that port      telnet localhost 2080     If it is listening  it is able to respond

User · Answer

In Ubuntu  Try sudo ufw allow  lt port number gt   to allow firewall access to both of your server and db

User · Answer

From the standpoint of a Checkpoint firewall  you will see a message from the firewall if you actually choose Reject as an Action thereby exposing to a propective attacker the presence of a firewall in front of the server  The firewall will silently drop all connections that doesn t match the policy  Connection refused almost always comes from the server

User · Answer

1 Check your server status   2 Check the port status   For example 3306 netstat -nupl grep 3306   3 Check your firewalls  For example add 3306  vim  etc sysconfig iptables   add -A INPUT -p tcp -m state --state NEW -m tcp --dport 3306 -j ACCEPT

User · Answer

I get the same problem with my work computer  The problem is that when you enter localhost it goes to proxy s address not local address you should bypass it follow this steps  Chrome    Settings    Change proxy settings    LAN Settings    check Bypass proxy server for local addresses

User · Answer

Connection refused means that the port you are trying to connect to is not actually open    So either you are connecting to the wrong IP address  or to the wrong port  or the server is listening on the wrong port  or is not actually running   A common mistake is not specifying the port number when binding or connecting in network byte order

User · Answer

The error means the OS of the listening socket recognized the inbound connection request but chose to intentionally reject it     Assuming an intermediate firewall is not getting in the way  there are only two reasons  that I know of  for the OS to reject an inbound connection request   One reason has already been mentioned several times - the listening port being connected to is not open     There is another reason that has not been mentioned yet - the listening port is actually open and actively being used  but its backlog of queued inbound connection requests has reached its maximum so there is no room available for the inbound connection request to be queued at that moment   The server code has not called accept   enough times yet to finish clearing out available slots for new queue items     Wait a moment or so and try the connection again   Unfortunately  there is no way to differentiate between  the port is not open at all  and  the port is open but too busy right now    They both use the same generic error code

[c] What can be the reasons of connection refused errors?

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