Questions tagged [port]

A port provides a location for an application to interface with the network. If there is no application that is listening at a particular point, data sent there will never be used.

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467 votes
14 answers

Test if a port on a remote system is reachable (without telnet)

In the old days, we used telnet to see if a port on a remote host was open: telnet hostname port would attempt to connect to any port on any host and give you access to the raw TCP stream. These days,...
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235 votes
1 answer

What is port forwarding and what is it used for?

There are a lot of questions on 'port forwarding', but there doesn't seem to be one that clearly states what it is and what it's used for. So: What is port forwarding? What is it used for, and why ...
207 votes
3 answers

What are CLOSE_WAIT and TIME_WAIT states?

When I do netstat -a on my Windows machine, I get a listing of the ports with one of the four states: - LISTENING - CLOSE_WAIT - TIME_WAIT - ESTABLISHED What do CLOSE_WAIT and TIME_WAIT mean/...
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149 votes
5 answers

Finding the process that is using a certain port in Linux

I'd like to be able to find out which process is currently using a certain port in Linux. Is there any way to do this?
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140 votes
15 answers

Manually closing a port from commandline

I want to close an open port which is in listening mode between my client and server application. Is there any manual command line option in Linux to close a port? NOTE: I came to know that "only ...
user avatar
130 votes
6 answers

How to telnet to an IP address on a specific port?

Can anyone tell me how to telnet to an address using a specific port? I've tried the following: telnet I suppose a route just hasn't been set up between the two hosts? What I am trying ...
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68 votes
5 answers

Do web browsers use different outgoing ports for different tabs?

In a web browser that supports having multiple tabs, such as Firefox, do different tabs that go to different website domains use a dedicated port for each domain?. Or does the browser use a single ...
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67 votes
6 answers

PID:4 using Port 80

I was trying to install Zend Server CE on my computer but when I got to the point were I need to choose the port for my Web Server it says: "Web Server Port: 80 Occupied". So I decided to check what ...
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66 votes
2 answers

Why was port 80 chosen as the default HTTP port and 443 as the default HTTPS port?

Why was port 80 chosen as the default HTTP port and 443 as the default HTTPS port? Is there a reason or was it is just defined that way?
45 votes
3 answers

How to find out what is running on localhost port

I have something running at port 9090 on my local machine. It's probably something I set up long ago and forgot about... how can I find out what it is? I am using Windows 8.
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41 votes
4 answers

Is there any harm of leaving Ethernet outlet unplugged?

I was wondering if leaving an active Ethernet port with no plug in it was safe . We have one in our kitchen right next to our face level and I was wondering if leaving it unplugged in the open was ...
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40 votes
3 answers

No idea what is listening on port 80 in OS X

I'm on OSX Mountain Lion 10.8.3, and I've freshly rebooted my Mac. I want to start a service (like Apache on port 80), but there is already something going on with port 80: telnet localhost 80 ...
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38 votes
4 answers

How can I check which ports are busy and which ports are free on my Linux machine?

Is there any command line command or any other way to find and list out the busy and free port numbers on my Linux machine?
36 votes
4 answers

What port does 'ping' work on?

Is there any particular port number that the ping command works on by default? Also on a Linux system, is there a way to figure out by yourself which port numbers it runs on and configure a different ...
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33 votes
3 answers

How are source ports determined and how can I force it to use a specific port

When I connect to this changes to Then a connection to me opens on [My IP Address]:63998. My question is how is 63998 port choosen and is there a way of ...
31 votes
2 answers

SSH: Troubleshooting "Remote port forwarding failed for listen port" errors

Question: Why does ssh -N -R 2222:localhost:22 <bluehost_user>@<bluehost_ip> result in a "Remote port forwarding failed for listen port" error? The objective is to establish a ...
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29 votes
11 answers

Utility to open TCP port to listen state

Is there some basic utility to open a specific network TCP port on my machine? I need to test how my program deals with ports in the listening state.
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28 votes
3 answers

Are there good alternative HTTP ports rather than port 80?

I have been looking for some documentation on alternatives to port forwarding to port 80. I have a dedicated Linux machine on a home router, and apparently utilizing port 80 is not an option. Are ...
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28 votes
10 answers

Linux command get unused port

I'm looking for a command or script which returns an unused port on my ubuntu linux system. I have look on internet and the only thing I find is about the used/Listen port with the nestat command. ...
27 votes
1 answer

Why can I not connect to a reverse SSH tunnel port remotely, even with GatewayPorts enabled?

I require constant SSH access to a host in our department, whose IP address is dynamically allocated. I've set up a remote SSH tunnel from the target host to one of our hosts that does posess a static ...
26 votes
5 answers

Should I run my small website in port 80, 8080, or 81?

I am running a small website using nginx. Since there's (probably) not going to be a lot of traffic in my server's lifespan and to avoid random DoS attacks, I am considering setting the web server to ...
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26 votes
4 answers

How to kill a particular tcp connection in windows?

On Linux we can kill an Established TCP Connection using tcpkill command. For example, to drop all connection to/from a particular IP: tcpkill host ipaddr Or similary to kill all connection ...
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26 votes
3 answers

Difference between port mapped and memory mapped access?

Can anyone explain what's the difference between port mapping and memory mapping, and what having both accomplishes? Why is there port mapped, how does it differ in structure from memory maps, and is ...
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26 votes
2 answers

What port or ports are used for File sharing in windows?

I want to know on the windows operating system, what is the port number for the file sharing service? For example as you know the port number for HTTP service is 80. So I need to know the port number ...
25 votes
7 answers

How to kill a process by port on MacOS, a la fuser -k 9000/tcp

On linux I can kill a process knowing only the port it is listening on using fuser -k 9000/tcp, how do I so the same on MacOS?
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24 votes
3 answers

How to detect if a network is blocking outgoing ports?

How do I confirm if my network is blocking outgoing ports? I'm having issues accessing services on servers running on ports other than port 80 and 443. For example, I cannot ssh into any of my ...
23 votes
3 answers

How to block all ports except 80,443 with iptables? [duplicate]

Blocking all ports(in and out) is easy but it's hard with the word "except". I don't know any rules that satisfies the condition. PS: I know this question is nothing new. But in fact, I didn't find ...
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22 votes
2 answers

Port 5357 TCP on Windows 7 professional 64 bit?

Is there a reason this port is open, a quick Nmap scan and Nessus scan reveal it's open, why? Are there any ramifications if I close this port via the firewall rule set? Or does anyone here now more ...
21 votes
1 answer

802.1X: What EXACTLY is it regarding WPA and EAP?

I understand 802.1X to be some sort of port authentication control. However, when I was checking out the encryption settings for my wireless I found 802.1X in a drop down along with WPA2, WPA and WEP, ...
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20 votes
3 answers

Figure out non standard ssh port

I have this server that is configured to use another port instead of 22 for ssh. How may I figure out which port number it is?
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20 votes
7 answers

Apache Server on Windows 7 opening up ports?

I have installed Apache 2.2.14 on Windows 7 and can view my web pages using both http://localhost and but when I try to access the server from another computer on the same router, it ...
  • 7,728
20 votes
5 answers

How to access NodeJS server on LAN?

I'm not the most knowledgeable guy ever with networking, but here goes... I've created an application with NodeJS and I'd like to test the application on my LAN with my family. The application ...
20 votes
1 answer

Why is "nc -l xxxx" not opening a port?

I'm trying to get netcat to listen on port 4444, but it doesn't seem to be working. I am checking to see if the port is open using nmap, but it doesn't pick it up and I can't figure out why. I have ...
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19 votes
11 answers

How to "restart/repair" an USB port?

My laptop has two USB ports, but one is broken, so I use a USB hub in the other good USB port. In that USB hub, I use a mouse and keyboard. Suddenly, that USB port doesn't detect the mouse and the ...
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19 votes
3 answers

Does it matter what UDP port a WOL signal is sent to?

i have seen many WOL instances use port 7 and many use port 9, does it matter? Isn't it just looking for a WOL packet at layer 2 or ethernet?
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19 votes
3 answers

Find out what program runs in the java.exe process

I have a problem: always when my computer starts, there is a java.exe process listening in the port 7676. I want to find out what it is to be able to delete it. Is there any way that I can find that ...
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18 votes
4 answers

How to specify VNC port number with Mac OS X built-in VNC client?

Is it possible to specify VNC port number in built-in VNC client of Mac OS X? I'm trying to connect to Xen VPS machine with Finder's built-in VNC client. I used address like this. vnc://server:port ...
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17 votes
5 answers

Why are USB ports sometimes referred to as serial ports and called COM?

As far as my understanding of computer ports goes, A serial port is a 9 pin plug such as the one showed here and it is also called a COM port. USB ports are a different standard from serial ports. ...
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17 votes
5 answers

Kill what ever is running on port 8080

I am trying to run a GAE app on localhost:8080, but it was apparently occupied, even after shutting down and restarting my computer. I ran sudo lsof -i :8080. Lo and behold there is something sill ...
17 votes
6 answers

how to disable feature that opened port 445 on windows server?

I'm trying to disable services that I do not need, to improve latency and improve security. I found that port 445 is still open by doing telnet on localhost and port 445. As I do not need port 445, I ...
17 votes
4 answers

How to open TCP port in Ubuntu 10.10?

How to open TCP port in Ubuntu 10.10 ?
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15 votes
3 answers

Outgoing VPN PPTP: How to check if TCP port 1723 and GRE protocol port 47 are blocked or not in Windows 7?

I am trying to connect to a VPN Server (BestUKVPN) but I'm failing each time I try. I get a "691 error" but the username and password are OK. I searched and I am told that "port 1723" or 'GRE ...
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15 votes
5 answers

What ports are used by an application [duplicate]

I'm testing an application which opens its own ports (acts as a server for these ports, hence listens at that ports) and where the same application connects to ports bound by other applications (acts ...
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15 votes
3 answers

Netgear router listening on port 32764?

I've got a Netgear DG834G running firmware V5.01.01. From the LAN side, if I port scan it, it's listening on tcp port 32764. Trying to telnet into this port gives me the response MMcS\xff\xff\xff\xff\...
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14 votes
6 answers

Why does my USB cable have an extra red plug?

My girlfriend just got a new ebook reader — a jetbook — that came with an unusual USB cable. One end is a regular USB mini B head, but the other end has two plugs. Both are USB non-mini ...
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14 votes
4 answers

Is there a simple way to detect ISP port blocking?

Is there a way to tell the difference between my ISP blocking traffic on certain ports and my NAT router/firewall blocking that traffic? The sites “Shields Up” and “Can you see me” show my ports ...
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14 votes
6 answers

Why is System listening on port 8000?

I noticed by accident today that I have some unknown webserver listening on port 8000. Opening http://localhost:8000 just returns 404, so I don’t get any hint what exactly is listening there. I’ve ...
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14 votes
3 answers

What are ports and protocols really?

I hear people talk about ports and protocols (in relation to computer networking), and they often provide analogies for them (for example: "a port is much like a shipping port, it sends and receives ...
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14 votes
1 answer

Multiple processes listening on the same port; how is it possible?

Multiple processes are listening on same port. But as far as I know only one process can listen on a port. Is it possible (how?) that multiple processes can listen on same port? $ sudo lsof -n -i :80 ...
  • 143
14 votes
3 answers

Determining what process has bound a port (without listening) on Windows

If I want to find out what process is listening on what socket, I can use netstat/TCPview and will immediately see it. However, it is possible to bind to an address without listening. If this is done, ...
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