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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1answer
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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 ...
105
votes
3answers
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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/indicate?
92
votes
3answers
81k views

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?
80
votes
8answers
256k views

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 ...
58
votes
13answers
188k views

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 ...
50
votes
2answers
5k views

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?
42
votes
4answers
6k views

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 ...
30
votes
4answers
107k views

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 ...
16
votes
7answers
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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 http://127.0.0.1 but when I try to access the server from another computer on the same router, it ...
16
votes
4answers
52k views

How to open TCP port in Ubuntu 10.10?

How to open TCP port in Ubuntu 10.10 ?
13
votes
1answer
22k views

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, ...
13
votes
2answers
31k views

Netcat on Mac OS X

Is anybody else not able to get nc -lp 8888 working on Mac OS X? Is there another way to get this to work?
13
votes
2answers
42k views

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.
13
votes
8answers
37k views

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 on listening state..
13
votes
2answers
29k views

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 ...
12
votes
4answers
77k views

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?
12
votes
1answer
1k views

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, ...
11
votes
3answers
6k views

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 ...
11
votes
2answers
20k views

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 ...
11
votes
3answers
29k views

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 ...
10
votes
3answers
16k views

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?
10
votes
6answers
8k views

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 ...
10
votes
4answers
57k views

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 ...
10
votes
4answers
12k views

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 ...
10
votes
1answer
10k views

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 ...
10
votes
1answer
60k views

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 ...
10
votes
1answer
1k views

268 Ports Associated with Chrome

I'm currently using a Windows box, running Chrome 27 on the dev channel, and I have what I believe to be an unusually large number of listening connections connected with the process. The following ...
9
votes
5answers
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How do I find out what service is using a certain port?

Port 22 specifically. I installed freeSSHd on a Windows Server 2008 box that only runs IIS. When I try to start the SSH Service, it tells me that the port is already being used. How can I find out ...
9
votes
5answers
878 views

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 ...
9
votes
4answers
43k views

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 ...
9
votes
6answers
8k views

Port scan revealed port 1111 open. What is it?

I am new to systems administration and have a new server running a website with http (at port 80), https (at port 443) and ssh (at port 22). I did an nmap port scan using my personal laptop and other ...
9
votes
1answer
2k views

How do I make Skype not use port 80?

I need this port for apache, how do I forbidden Skype from trying to use this port any more?
8
votes
4answers
4k views

Accessing freenode without ports

I'm at a computer where most ports are blocked. Is there still a way to access freenode to ask about programming questions through some webinterface?
8
votes
1answer
12k views

How do I determine which application is using port 8080? [duplicate]

Possible Duplicate: Finding the process that is using a certain port in linux I have an Ubuntu Server setup, where I'm trying to set up a daemon that wants to have access to port 8080. When ...
8
votes
7answers
16k views

WWAHost.exe using same port as Apache

I have installed XAMPP 1.8.1. on my Windows 8 64bit machine. I'm now facing a problem with ports. This is what I got from XAMPP Control Panel: 11:52:43 AM [Apache] Problem detected! 11:52:43 ...
8
votes
1answer
15k views

Why does google chrome need so many ports open?

I just did a port check with CPorts and I find that google chrome has so many local ports open in the range of 7713 - 7794. They are all connects to 80 or 443 on the other end. Why does google ...
7
votes
8answers
107k views

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 ...
7
votes
3answers
51k views

How to know which port is busy or free on Windows 7? [duplicate]

Possible Duplicate: How can I see all active connections? I have some conflict of ports and my WampServer didn't work, so I have to know which port is used. Is there a command line command ...
7
votes
5answers
7k views

How can I find out which process is listening on a port on linux? [duplicate]

Possible Duplicate: Finding the process that is using a certain port in Linux How can I find out which process is listening on a port on linux?
7
votes
4answers
9k views

Open port 5672/tcp for access to RabbitMQ on Mac

I have RabbitMQ in its latest version installed on my Mac with default configuration and when I'm accessing it from localhost there's no issue what so ever. But today I build a linux machine on local ...
7
votes
4answers
25k views

What is binding this port?

Something is serving content on my port 80, but I don't know what process is doing this. Is there any way to find out what process is bound to which port(s)? Update: This is the output of netstat... ...
7
votes
3answers
146k views

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 ...
7
votes
1answer
453 views

Is this how ftp works?

I just want to check if my understanding of ftp is correct. An ftp server listens at port 21. A client establishes a connection to the ftp server using a local ephemeral port that connects to the ftp ...
7
votes
3answers
13k views

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?
7
votes
4answers
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USB Ports Not Working

None of the USB ports work anymore on my HP EliteBook 2540p laptop which is running Windows 7 Pro SP1. By "not working," I mean if I try plugging in a thumbdrive or external HDD it does nothing ...
7
votes
1answer
9k views

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 ...
7
votes
4answers
43k views

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 ...
7
votes
1answer
4k views

What can the second LAN port be used for on a NAS?

I've got a NAS with 2 ethernet ports. I have one connected to the router. I read that the second could be connected to double the speed of data to and from the NAS. I don't need to do that, as the ...
7
votes
1answer
14k views

How can I close a port (seen open on netstat)?

I used netstat and I see some ports open that I want closed. How do I close them? The computer is a Mac running OS X
6
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2answers
2k views

Will cases with front USB port support USB 3.0?

If a computer case has a USB port in the front, will it support USB 3.0 if my motherboard supports it? Or does the case vendor need to specifically mention USB 3 support? (BTW, I haven't seen such ...