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How to Choose a Default Port Number for a New Network Service?

Last updated: March 18, 2024

1. Introduction

In the context of computer networks, a port is an endpoint for communication between applications (or network services). Each port has a port number for identification. Thus, a network service can use one or more ports by specifying their numbers.

By definition, there are 65,536 possible ports for use. However, many of them have a specific purpose or have already been assigned to some service. In this article, we’ll study how to choose a default port number for a new network service.

The main issue we have to deal with is choosing a port that’s not being used by any other service. Otherwise, there’s a good chance that our new service will eventually be executed on a machine with another service running on the same port. This would prevent both services from working.

To have a full view of the problem, we’ll first understand the subdivision of the port range. Next, let’s learn how to choose ports other than those used by well-known services. Then, we’ll see how to avoid conflicts with services running on our machine or the local network. Finally, we’ll briefly look at how to request an official assignment of the chosen port for our service if desired.

2. Understanding the Subdivision of Port Ranges

The full range of possible port numbers extends from 0 to 65535. However, properly using this large but limited port range requires global coordination. In this sense, RFC6335 designates the Internet Assigned Numbers Authority ( IANA ) as responsible for the assignment of these ports.

IANA handles port number assignments through procedures also specified in RFC6335. In short, the specification subdivides the full range of port numbers into three smaller ones. Each one of them is intended for different uses, as described in the table below:

System Ports and User Ports are available for assignment through IANA, which requires the IETF review or the IESG approval. However, the Dynamic Ports range has been specifically set aside for local and dynamic use, so it can’t be assigned through IANA.

The possible states for each port are Assigned, Unassigned, or Reserved. So, the only ports free to use are those with Unassigned state.

2.1. From Which Sub-range Should We Choose a Port?

The System Ports range (also known as the Well-Known Ports) is both the smallest and the most densely assigned. So, the requirements for new port assignments in this range are much more strict than those for the User Ports range (also called Registered Ports). Therefore, ports in the System Ports range are only used by very well-known services and protocols.

Ports in the Dynamic Ports range are considered ephemeral ports, i.e., they’re only for temporary and dynamic use. Therefore, we should never use a port in this range as a service identifier since there’s no guarantee that ports will be available for the service.

Thus, in most cases, we should look for a free port in the User Ports range when choosing a default port for a new service.

3. How to Avoid Conflicts With Well-Known Services?

Nowadays, there’s a wide range of network services (and protocols) used worldwide. Most of them are well-known services that have assigned ports in the IANA. Other services, although well-known, don’t have IANA-assigned ports for some reason.

Next, let’s see how to avoid selecting a port that services in both cases are already using.

3.1. Check Allocated Ports in IANA

For not choosing a port assigned by IANA, we need to check the IANA port number registry . It lists all port assignments and their respective services. In this case, the ports available are the ones that aren’t listed in the registry or have the Description field marked as Unassigned .

Given the large number of port assignments, it can be challenging to find available port numbers in the desired range. For convenience, we can download the IANA port number registry in CSV format and use the Python script list_iana_available_ports.py below to list the available ports in any given range.

To use the script above, we just need to run the command below, replacing <port-start> and <port-end> according to any range of our choice and <csv-file-name> with the actual name of the downloaded file.

It may be a good idea to select one or more of the available ports according to IANA. For example, we may use the provided script to find available ports ranging from 2000 to 3000 (which is a subrange of User Ports) and then select one or more ports.

After that, we can follow the next steps just to make sure that no other service is unofficially using the chosen port.

3.2. Check Ports Listed by NMAP

Some widely used services utilize ports that haven’t been officially assigned to them in the IANA registry. So, to avoid choosing a port used by one of these services too, we need to refer to an alternative (unofficial) but comprehensive listing.

An example of such a list is provided by NMAP.org . The NMAP list includes port assignments registered in IANA and others that have been detected by NMAP itself.

Thus, by accessing this list, we can check whether the port (or range) we selected in the previous step has also been identified by NMAP as frequently used by services. Since the port we’ve selected so far isn’t present in the NMAP list, we can follow the steps below to check further.

4. How to Avoid Local Conflicts?

Besides avoiding conflicts with widely used services, we also need to ensure that the chosen port doesn’t create conflicts with our organization’s own services. Next, we’ll see how to avoid conflicts with other services on our local machine or local network.

4.1. Check the Local System

Usually, Operating Systems (OS) have a file that maps services and their respective ports. Applications use it to convert human-readable service names into port numbers. Specifically, in Linux and MacOS, we can find this file at /etc/services , whereas, in Windows, its location is %windir%\System32\drivers\etc\services .

The services file includes the assignments made by IANA but also maps services related to the OS and others running on the local machine. For example, in a Debian-based distribution, the file includes a section named “Services added for the Debian GNU/Linux distribution” and another named “Local services”.

Hence, we can just open the file and search for the chosen port. So, if we don’t find the port in the file, we know that there are no local conflicts.

4.2. Check the Local Network

To check if another service on our local network is using the port we’ve chosen so far, we can use a network scanning tool. An example of such a tool is NMAP, which is widely used and available for various OSes , including Linux, Windows, and MacOS.

In short, NMAP has a command-line interface that expects some parameter (or command option) and a target host. The target host refers to the host that will be scanned. So, it can be a hostname or an IP address.

However, in our case, we don’t want to scan a specific target host but the whole network for open ports (ports being used by some service). Fortunately, the NMAP command line also supports multiple target hosts. There are many ways to do this , but one of the easiest is by using the CIDR notation.

This way, we can scan the entire network at once, specifying the target host in the format <network-ip-address>/<netmask> . For example, we can search for all open ports on the network 192.168.1.0/24 by typing the following command.

In addition, we can also scan only the port we’ve chosen later. The command below exemplifies a search for hosts using port 3000 on the network 192.168.1.0/24 .

5. How Can We Request a Port Assignment for Our Service?

Once we’ve chosen a port that’s currently available, we can request that the port be assigned to our service if we so desire. However, we should do this only if the service is genuinely distinct. Otherwise, IANA will probably not approve the port assignment.

For example, if the service is a new web application, instead of requesting a new port assignment, we should use the ports already assigned for this kind of service (such as 80 for HTTP and 443 for HTTPS).

Nevertheless, to make the request, we can submit an application for port assignment through the official IANA form .

6. Conclusion

In this article, we learn how to choose a port for a new network service. A good choice requires in-depth investigation to avoid choosing a port that’s already in use by another service.

The first step is to check the IANA port assignment registries. After that, we can consult unofficial registries and local port mappings and scan the network for ports in use.

In conclusion, these are the key steps to selecting a port number for a new network service, ensuring effective communication.

TCP/IP Ports and Sockets Explained

The IP address identifies the device e.g. computer.

However an IP address alone is not sufficient for running network applications, as a computer can run multiple applications and/or services .

Just as the IP address identifies the computer, The network port identifies the application or service running on the computer.

The use of ports allow computers/devices to run multiple services/applications .

The diagram below shows a computer to computer connection and identifies the IP addresses and ports.

If you use a house or apartment block analogy the IP address corresponds to the street address.

All of the apartments share the same street address.

However each apartment also has an apartment number which corresponds to the Port number.

Port Number Ranges and Well Known Ports

A port number uses 16 bits and so can therefore have a value from 0 to 65535 decimal

Port numbers are divided into ranges as follows:

Port numbers 0-1023 – Well known ports. These are allocated to server services by the Internet Assigned Numbers Authority (IANA). e.g Web servers normally use port 80 and SMTP servers use port 25 (see diagram above).

Ports 1024-49151- Registered Port -These can be registered for services with the IANA and should be treated as semi-reserved. User written programs should not use these ports.

Ports 49152-65535 – These are used by client programs and you are free to use these in client programs. When a Web browser connects to a web server the browser will allocate itself a port in this range. Also known as ephemeral ports .

TCP Sockets

A connection between two computers uses a socket.

A socket is the combination of IP address plus port

Imagine sitting on your PC at home, and you have two browser windows open.

One looking at the Google website, and the other at the Yahoo website.

The connection to Google would be:

Your PC – IP1 +port 60200 ——– Google IP2 +port 80 (standard port)

The combination IP1+60200 = the socket on the client computer and IP2 + port 80 = destination socket on the Google server.

The connection to Yahoo would be:

your PC – IP1 +port 60401 ——–Yahoo IP3 +port 80 (standard port)

The combination IP1+60401 = the socket on the client computer and IP3 + port 80 = destination socket on the Yahoo server.

Notes : IP1 is the IP address of your PC. Client port numbers are dynamically assigned, and can be reused once the session is closed.

TCP and UDP -The Transport Layer

Note : You may find reading the article on the TCP/IP protocol suite useful to understand the following

IP addresses are implemented at the networking layer which is the IP layer.

Ports are implemented at the transport layer as part of the TCP or UDP header as shown in the schematic below:

The TCP/IP protocol supports two types of port- TCP Port and UDP Port .

TCP – is for connection orientated applications. It has built in error checking and will re transmit missing packets.

UDP – is for connection less applications. It has no has built in error checking and will not re transmit missing packets.

Applications are designed to use either the UDP or TCP transport layer protocol depending on the type of connection they require.

For example a web server normally uses TCP port 80 .

It can use any port, but the web server application is designed to use a TCP connection. See TCP vs UDP

Here is a very good video that explains ports and sockets really well

Checking For Open Ports

Windows and Linux systems have a utility called netstat which will give you a list of open ports on your computer.

These articles show you how to use netstat on windows and on linux .

You can check the port status of remote machines using a port scanner line nmap .

You can install NMAP on windows,Linux and Apple. It can be used with a graphical user interface of as a command line tool.

Here is a useful article on using NMAP from the command line .

Here is a good video on using Nmap and also covers TCP/IP connection procedures which is useful for understanding ports.

References and resources:

TCP and UDP basics -Connecting to a website- This is for programmers but there is no coding just an explanation of ports and sockets.

Connection states – if you are wondering what established and listening and the other state descriptions mean. here is a good state diagram that it refers to.

Online port tester Collection of tools for port scanning and web server testing.

TCP/IP protocol suite explained
Port Forwarding Explained
IPv4 Basics

70 comments

I created an inbound UDP port (10512); but I am not able to see this port. I also tried creating other ports in the noted range with out any success. Registered Ports: 1024 through 49151 portqry —-> UDP port 10512 (unknown service): NOT LISTENING Thanks for any clarification

Have you tried writing a program to send/receive data on that port.What utility are you using to view the ports. Rgds

Sorry, no time to research and develop a program. it would nice. I am trying to use online tools. I think that I just learned that portqry works great for TCP. I am trying to use iperf3; however not enough hands on as of yet. I see that iperf3 created inbound rule TCP and UDP. I deleted the TCP. I need more flying hours. iperf3 -s -p 10512 ———————————————————– Server listening on 10512 ———————————————————– I am also trying to use netstat to see if the port is listening; however no progress on that end. netstat -ab

netsh firewall show state netsh will show UDP port on client computer with Win 11 PRO but not on the server 2019.

thanks for any input

client side >iperf3 -c 10.241.71.38 -u -p 10512 -b 10M

I’ve decided to try to mess around with port forwarding as a means to try to get me and my friend who live in the same town and use the same internet provider (Spectrum) to be able to connect to each other in games that do not have dedicated servers. Spectrum’s peer-to-peer is absolute trash, and we can never connect to each other playing games like Risk of Rain 2, Elden Ring, etc. I’m trying to find a port that would help us overcome the connection issues. Any advice?

I’m not a gamer and so I have never experienced these issues. However games have their own ports have you checked on the required ports for these games? Rgds Steve

Hi Steve, I have a requirement. We have a web application which is connected to a mobile/Android POS device. This web application connects via TCPIP. As of today, we have the connections that are initiated from the device. the URL and port # of the web server is configured in the device and the connection is initiated from the device. Web application will respond to a request from the device. We now want to initiate the request from the server. Can we add another port # for this new communication? Similarly, there is a 3rd communication that happens from the device on timed intervals. For this, we want to use a 3rd port. Is this a possible solution for this? Happy to discuss this separately too.

I assume that you are talking about a web server. A web server cannot start a connection. Rgds Steve

Respected Sir Thank you so much for this informative article. I am a first year IT student. Sir , if I visit any particular website for 15 minutes and visit various sections of this website (feedback/ contact us / about us etc) in such case, does my visit to various sections is considered as a single connection/ single session or they are considered as multiple connections / multiple sessions to this website? Also what is the role of session ID in TCP IP communication along with port and socket Thank you Sir Bhavesh

It is a single TCP/IP connection. If you close the tab and then revisit by typing in the url then you will get a new connection.

Just out of curiosity, if the user visits different pages on the website, won’t these be over a new TCP connection every time unless a long-lived HTTP is used?

No they will be a single connection just a different get command. HTTP now hold the connection open by default until you close the browser tab. Rgds Steve

Thanks Steve for making it vividly simple.

I have a problem with an application that uses fixed source ports in the communication with the server. If the communication ends for some reason the clients tries to put the communication up again using the same source port. The problem is that the server have not gotten a fin packet that takes down the communication and it still listens for the communication from the client in a ESTABLISHED status if you run netstat -a on the server. If the client had not used fixed ports I would think that the communication would reconnect with a new session because the client had used “+1” on its source port and the server would connect the communication with a new socket.

Is there a “best practice” rfc that explains why it is not a good idea to use fixed ports?

Not that I am aware.

Wonderful, I’ve sent it over email along with some info It runs on Ubuntu Thank you for your time on this and God bless Al

I have a software which creates 4 sockets with apparently random numbers (the person who developed left no documentation)

However, the client which connects to it only sends over port 9091

Is there a way to interconnect those random number sockets and port 9091 so the client is able to connect to the software?

Thanks in advance and God bless

Hi It sounds like the software is supposed to be a server which usually has fixed ports. What does the software do?

It receives video data, connects to a MariaDB server, and serves as an API to it, receiving calls from a mobile app and sending customer data back

I wonder if the reason why it opens 4 sockets is to receive and send video data and receive and send customer data

Either way, the problem is that it creates sockets of random numbers instead of a 9091 port which is what the android app uses

Below its log, hope that sheds some light and thanks

[0121/06/01 12:55:01][0000-00000001] SDSS int server v1.2.0 – b6 (01/03/2021) run up at Thu Jul 1 12:55:01 2021 [0121/06/01 12:55:01][0000-00000002] debug level set to 99 [0121/06/01 12:55:01][0000-00000003] args[ ./dvis -d99 ] [0121/06/01 12:55:01][0000-00000004] startup info follows: [0121/06/01 12:55:01][0000-00000005] stdin handle 0 [0121/06/01 12:55:01][0000-00000006] openSQL( 0x5f687580 ) [0121/06/01 12:55:01][0000-00000007] openSQL: Connection successful to ‘127.0.0.1’ as ‘sa’ [0121/06/01 12:55:01][0000-00000008] hostname being used is ‘stipra.com’ [0121/06/01 12:55:01][0000-00000009] get_ipaddress() [0121/06/01 12:55:01][0000-00000010] lo IP Address 127.0.0.1 [0121/06/01 12:55:01][0000-00000011] wlo1 IP Address 192.168.1.142 [0121/06/01 12:55:01][0000-00000012] lo IP Address ::1 [0121/06/01 12:55:01][0000-00000013] wlo1 IP Address fe80::d6a7:186d:aa86:5311 [0121/06/01 12:55:01][0000-00000014] get_ipaddress: returning an IP4 address of 192.168.1.142 [0121/06/01 12:55:01][0000-00000015] Running on server stipra.com IP address 192.168.1.142 [0121/06/01 12:55:01][0000-00000016] setsockopt returned 0, errno 11 [0121/06/01 12:55:01][0000-00000017] sockets created [0121/06/01 12:55:01][0000-00000018] 63420 [0121/06/01 12:55:01][0000-00000019] 29616 [0121/06/01 12:55:01][0000-00000020] 6052 [0121/06/01 12:55:01][0000-00000021] 43464 [0121/06/01 12:55:01][0000-00000022] wait_for_cmd(0x1) [0121/06/01 12:55:01][0000-00000023] stdin(0) [0121/06/01 12:55:01][0000-00000024] recv_d( 0, 0x7f90fdd4e010, 8 ) [0121/06/01 12:56:01][0000-00000025] recv_d: Select timeout, retrying [0121/06/01 12:57:01][0000-00000026] recv_d: Select timeout, retrying [0121/06/01 12:58:01][0000-00000027] recv_d: Select timeout, retrying [0121/06/01 12:59:01][0000-00000028] recv_d: Select timeout, retrying [0121/06/01 13:00:01][0000-00000029] recv_d: Select timeout, retrying [0121/06/01 13:01:01][0000-00000030] recv_d: Select timeout, retrying [0121/06/01 13:02:01][0000-00000031] recv_d: Select timeout, retrying [0121/06/01 13:03:01][0000-00000032] recv_d: Select timeout, retrying [0121/06/01 13:04:01][0000-00000033] recv_d: Select timeout, retrying [0121/06/01 13:05:01][0000-00000034] recv_d: Select timeout, retrying [0121/06/01 13:06:01][0000-00000035] recv_d: Select timeout, retrying [0121/06/01 13:07:01][0000-00000036] recv_d: Select timeout, retrying [0121/06/01 13:08:01][0000-00000037] recv_d: Select timeout, retrying [0121/06/01 13:09:01][0000-00000038] recv_d: Select timeout, retrying [0121/06/01 13:10:01][0000-00000039] recv_d: Select timeout, retrying [0121/06/01 13:10:01][0000-00000040] wait_for_cmd: Initial receive is not 8 bytes [0121/06/01 13:10:01][0000-00000041] pipe broken exiting

Sorry don’t know, It looks like it is creating client connections but not sure what to. When you say it receives video data I assume that that is coming in on a port. The database would need another. The mobile app is used to view the video I assume. Is any part of it working. Where is the mobile App located(internet or same network). Is this a standard kit or is it put together by yourself? Rgds Steve

The software creates 4 sockets with random port numbers but none of them are the port 9091 which the APP uses. The mobile App is on the internet.

The software connects to a tunnel connection 10.8.0.0, which leads me to believe it requires the creation of some kind of tunnel to capture anything received from the internet on port 9091 from 192.168.1.142 and forward it to those 4 sockets through some kind of dynamic port forwarding thing or something like that

I tried to use ssh -D 192.168.1.142:9091 -N -f [email protected] and I am able to telnet 192.168.1.142 and connect the app, but no data seems to go or come back 🙁

The software connects to the database, and that’s actually the only thing it is doing well

Does it have any setup instructions. Is it off the shelf software and does it have a website that I can take a look at. Rgds Steve

It is a bespoke software made by a person who left the company and never left any documentation. It is developed in C++ 32 bits I can send it to your email which I believe is [email protected] as it is rather small, along with how to run itm (the little I know at least)

That email will work is it for windows or linux?

Hi, I have a question, is it possible for me to run 2 applications and connect to different ip but using same port number (example 6000) ?

Yes you are doing that when you connect to two different websites as they both use port 80 rgds steve

So I have a question. Let’s say there is a webserver A which hosts a website and that server A has the port 443 open and let’s say I have written a code as part of a webpage on that website and that code connects to a remote server B to get some data. Can server A somehow restrict me and only allow connections to the port 443 on the remote server B and not allow me to connect me to any other port on remote server B? Have you seen such a restriction before and if yes then what would be the reason behind such a restriction? Thank you

Not quite sure exactly what restriction you mean but you can restrict on destination port and ip and source port and IP if that helps rgds steve

Hi Steve, So here is the scenario. The webserver A has the port 443 open for any incoming requests. The webserver A hosts a website and one of the pages of that website has C# code which makes API calls to a remote server B. I was told by the network admin of Webserver A that the C# API call should be made only to the port 443 of the remote server B. Currently the remote server B has port 7093 open and it’s listening to any API requests on that port. So my questions are:- 1. Is it possible for the network admin to disallow API calls to ports other than 443? 2. What could be the reason for such a restriction? After all, how can restricting a destination port give you any sort of advantage? Port is just a number on which the server listens. Please help. Thank you

Yes you can filter incoming traffic on port, ip address and protocol even on basic firewalls. Restricting ports is for security reasons Rgds Steve

Minor formatting issue: “{outline]Each end of the connection will have a socket.{/outline]”

Tks for pointing that out. Rgds Steve

Very well explained, thanks a lot!

Steve, this was very well explained, thank you.

Thank you very much! Realy clear explanation.

I want to read a data from a machine which supports open protocol if the machine is in network and if I know IP address and port number(socket) how can I read a data from it(I know it send and receive data in packet format )

Hi not sure what you mean by supports open protocol. Rgds Steve

Thank you, Steve! Is it possible with TCP/IP sockets to send requests to one IP:PORT and listen for responses on a different IP:PORT. E.g. we want to send to a load balancer IP but listen for response on localhost.

Hi Not quite sure of what you mean exactly but load balancing is quite common. This might help https://www.citrix.com/glossary/load-balancing.html

Question: When a program on your computer sends or receives data over the Internet it sends that data to an ip address and a specific port on the remote computer. How does my computer know what port a specific application is working on another computer to populate the TCP Header?

When Machine A connects to machine B. The source ip and port are contained in the connection packet as well as the destination port and IP address. The IP packet contains the ip addresses and the tcp layer contains the port numbers see https://en.wikipedia.org/wiki/IPv4 https://en.wikipedia.org/wiki/Transmission_Control_Protocol

Hi Steve, Thanks for the tutorial can you please help me with the following issue I have multiple devices connected to the same network and I want to transfer data across them, how can I transmit the data the IP of some devices changes after a particular time I can keep the port number constant but the devices don’t know each others IP address and also I don’t want to use UDP because it is not reliable

Hi You need to use DNS.Because the IP changes you need dynamic DNS. Most devices have MDNS enabled. See this article on my other site https://stevessmarthomeguide.com/name-resolution-and-dns-on-home-networks/ To seen if mdns is working try ping computer_name.local However the easiest solution is to give them static IP addresses. Rgds Steve

Great site. I have a quick question. If I receive a UDP datagram using recvmsg(), will the msghdr structure be filled out with the sender’s IP and port (in the msg_name field, which is a sockaddr struct)?

Many thanks.

Hi Haven’t programmed c with UDP but according to IBM then yes for ip address but doesn’t mention the port. https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.1.0/com.ibm.zos.v2r1.hala001/rcvm.htm rgds steve

hi ,I have some questions When using TCP protocol, the client must use in its message the IP address and Port number of the server. And it must also include its own IP address and port number. why?

4- When using UDP protocol, the client is required to use in its message the IP address and Port number of the server. But it is not required to include its own IP address and port number.why?

TCP is a connection orientated protocol and so the destination device needs to know who to send a reply to. UDP is connectionless and so doesn’t require a response and hence the source IP address is optional. Rgds Steve

really very useful..thanks for your explanation

Can Server and client share the port number, eg : Server is listening at port num : 51001 and client also listens on the same port num : 510001 .

Can you pls explain this

Yes providing they are on different hardware. A port is simply a door into the machine the numbers themselves aren’t really important except for the conventions already adopted and standardised. Machines use 16bits for the port numbers hence the limitation of 64,000.

16 bits = 1+2+4+8+16+32+64+128+256+512+1024+2048+4096+8192+16384+32768 = 65535

Good job Steve. I have a question, and it goes like this: if i have 2 browsers from my PC connecting to the same service, for example both browsers are connecting to google.com, does that mean that the two browsers from my computer are connecting to the same socket in the google server? Meaning can more than one socket connect to a socket at the same time?

Yes they use the same IP and port on the Google server but different ports on the client. rgds steve

Hi, Thanks for this information sharing. It is very well explained. I have following doubt, What I understand is TCP protocol takes care of data transmission error that duplication of packets or packet in true form delivered to other end. This is not done in UDP protocol. But when I see the Schematic of TCP, UDP & IP in your article I do not find any block for error checking in TCP where as UDP has checksum. Could you please clear my doubt.

The TCP packet also has a checksum which isn’t shown in my schematic you can see the full structure on wiki https://en.wikipedia.org/wiki/Transmission_Control_Protocol However it is the ack and nack messages that are responsible or making sure all of the data is received. Rgds Steve

In above example, google application/service and yahoo application/service both uses same port number i.e:80. Then there should be ambiguity that is to which application/service it should refer to either google or yahoo ;How it knows that it is google or yahoo as both has same port number? Answer will help me alot.

Google and Yaoo have different IP addresses. When you connect to google you use Google_IP +port 80. When you connect to Yahoo you connect to Yahoo_IP + port 80. Does that make sense? rgds steve

The IP is the who and the Port is part of the how.

The IP address of google and yahoo is different. say for google 172.13.73.130 and for yahoo 172.23.73.128 so even accessing the same port the two sockets will be totally different and hence different connections.

using the real world analogy two rooms of two different apartments may have the same room number and hence two server system may have same port number as well.

The port number 80 is the open port of server.here Google server had an open port (80) also Yahoo had an open port (80).

Both Google and Yahoo had different IP addresses.

If I want to connect Google server,I will open a new port,for example I will open port 5000, at the same time I will open another port 5002 to connect with Yahoo server.

My IP + 5000 — connects — Google IP + 80

My IP + 5002 — connects — Yahoo IP + 80

Great work!

Good Job!! Well Explained

Hi! keep up the good work. I have few doubts though, hope you can clear them: 1. Can you tell if a server uses a single port 80 on all of its connections to clients? Or is it used only by the Welcoming socket? Can port 80 handle multiple connections simultaneously?

A port (e.g port 80) can handle multiple connections each connection is a socket and will have a different source IP address and port number.

No… a session needs to be established at said layer. A is lessening on port 443 (SSL) for incoming packets and firewall infront is in addition to alllowing 443 to A also policing 25, 80 etc Whatever….

Excellent explanation. Thankyou!

very good information

The way you explain ed it, now it’s very easy understand the whole thing thanks alot sir .

Complete details about the TCP / IP ports and the sockets. in this article .The infographic is so good that anybody can understand at a glance. I request the author to post more articles on networking.

Common Ports Cheat Sheet: The Ultimate List

Perhaps you’re angsty that you’ve forgotten what a certain port number meant. Rest assured, you don’t have to remember all 65,535 port numbers. With so much information to remember, it’s understandable if you forget a common port. That’s why we put together this cheat sheet of common network ports for you.

A crucial domain of expertise in IT-related certifications such as Cisco Certified Network Associate (CCNA) and those of CompTIA is port numbers and associated services , which this common ports and protocols cheat sheet covers. If you want to remember a port number or protocol, this cheat sheet will help everyone, from students to professionals.

Get a copy of this common ports cheat sheet here to keep on your desk. When you're ready, scroll below to find the port you’re looking for.

Common Ports Cheat Sheet Search

Search our Common Ports cheat sheet to find the right cheat for the term you're looking for. Simply enter the term in the search bar and you'll receive the matching cheats available.

Common Ports and Protocols Cheat Sheet

The following tables cover services (and malware) that use common TCP ports and some UDP or SCTP ports.

Well-known/System Ports: 0 – 1023

Well-Known Ports: Unencrypted vs Encrypted - Graphic by author

Registered Ports: 1024 – 49151

The Registered Ports Used by Popular Services - Graphic by author

Dynamic/Private Ports: 49152 – 65535

You may use these ports for custom applications free from concerns that it may clash with existing processes.

The Most Common Ports for Exams

If you’re studying for IT certifications such as CCNA , focus on these ports:

We hope that you found this cheat sheet useful. Familiarity with ports and protocols is vital to building secure applications and troubleshooting problems on computer networks. Whether you're studying or working, this cheat sheet of common network ports will help you in academic and professional settings.

For further resources, or if you’re curious about how ports and protocols fit into cyber security, look into network security courses available with our StationX Accelerator Program .

Frequently Asked Questions

FTP: ports 20-21; SSH/SCP: port 22; HTTP: 80; HTTPS: 443; POP3: 110; POP3 over SSL: 995; IMAP: 143; IMAP over SSL: 993. We recommend you download the graphic in Well-known/System Ports .

It depends on whether you’re referring to system ports (1024) or want to include ports registered with apps (49152) because system ports range from 0 through 1023, and registered ports span 1024 – 49151.

FTP: ports 20-21; SSH/SCP: port 22; Telnet: 23; SMTP: 25; DNS: 53; HTTP: 80; POP3: 110; IMAP: 143; HTTPS: 443.

FTP: port 21; SSH/SCP: 22; Telnet: 23; SMTP: 25; DNS: 53; POP3: 110; IMAP: 145; HTTP: 80; HTTPS: 443; MySQL: 3306; RDP: 3389; VNC: 5900.

The following are the three types of ports with corresponding port number ranges: • Well-known/System ports: 0 – 1023 • Registered ports: 1024 – 49151 • Dynamic/Private ports: 49152 – 65535

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Nathan House is the founder and CEO of StationX. He has over 25 years of experience in cyber security, where he has advised some of the largest companies in the world. Nathan is the author of the popular "The Complete Cyber Security Course", which has been taken by over half a million students in 195 countries. He is the winner of the AI "Cyber Security Educator of the Year 2020" award and finalist for Influencer of the year 2022.

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Nathan, thank you for supplying this sheet. It comes in handy when you’re trying to remember what a particular port is used by.

Our pleasure.

Thank you, Nathan

This is a great single point to reference all default ports. Thank you!!!

Very good, it will be in front of me!

Ports on computers are required for networking, and without them, the computer would be completely isolated and it would be unable to communicate with other devices. So thank you for proving this list of the Common TCP and UDP Port numbers.

After resetting my router cause the password got changed and all the setting were changed to gain access to my computer. I spent about 20 minutes setting up the router. It appears the router never got set up from the cable company when it was installed. So if you have not done so lately check your router and settings.

Cool, Thanks for sharing!!

Sorry Nathan, i did not leave a comment for this “Common Ports” Chart last-week. I am glad i signed up to your news letter you are a good researcher. thank you for sharing with us all..

Nathan, I must thank you for these cheat sheets! They’ve been great on my learning and certification journey!

Thank you too!

Really really useful.Thanks a lot!!

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10-A.1.3: TCP/IP Fundamentals - Ports and Segments

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Network Ports

The physical ports on your computer allow it to communicate with peripheral devices such as your keyboard and mouse and to connect with internet devices via Ethernet cables.

Within computer networking, ports serve a similar purpose. When a computer system seeks to connect to another computer, the port serves as a communication endpoint. It is also possible for different services running on the same computer to expose various ports and communicate with one another using these ports. In simple terms, if a software application or service needs to communicate with others, it will expose a port. Ports are identified with positive 16-bit unsigned integers, ranging from 0 to 65535. Other services use this port number to communicate with the service or app. Port numbers are divided into three ranges: well-known ports, registered ports, and dynamic or private ports.

Well-known Port Numbers:

Network Segments

Network segments are used to divide a network into multiple segments or subnets, each acting as its own small network. By doing this network administrators can control the flow of traffic between subnets, improve monitoring, boost performance, localize technical issues and enhance security. Below is an example of a network segment from Cisco's Packet Tracer. One segment is on the left, and another segment is on the right.

Each of the segments has its own network ID, which is part of the IP address that is assigned to the devices in each subnet.

2 Network segments. The segments are separated by a router. Each segment has its own network number, which is part of the IP address.

Adapted from: "14 common network ports you should know" by Kedar Vijay Kulkarni , OpenSource.com is licensed under CC BY-SA 4.0

Port Number Lookup

If you are not sure that Port Numbers you are going to use has been assignned for what purpose. You can lookup our TCP ports database and find details related to assignment Port or Protocol assigned by IANA (Internet Assigned Numbers Authority).

Port Numbers and Protocols

TCP and UDP are two different protocols that are used for transmitting data over a network. TCP (Transmission Control Protocol) is a connection-oriented protocol that ensures that data is delivered reliably and in the correct order. UDP (User Datagram Protocol) is a connectionless protocol that does not guarantee the delivery of data or the order in which it is delivered.

Here are some common port numbers that are used by TCP and UDP:

TCP port numbers:

Port 80: HTTP (Hypertext Transfer Protocol)
Port 443: HTTPS (HTTP Secure)
Port 21: FTP (File Transfer Protocol)
Port 22: SSH (Secure Shell)
Port 25: SMTP (Simple Mail Transfer Protocol)
Port 155: NETSC

UDP port numbers:

Port : DNS (Domain Name System)
Port 67: DHCP (Dynamic Host Configuration Protocol)
Port 69: TFTP (Trivial File Transfer Protocol)
Port 123: NTP (Network Time Protocol)

Note that these are just a few examples, and there are many other port numbers that are used for various purposes.

For port numbers lookup, the official database of ports and protocols from IANA (Internet Assigned Numbers Authority) is used. IANA is an organization that manages Internet protocol parameters, as well as IP address spaces and top-level domains.

Diffrent Port Number Ranges?

The entire range of port numbers (from 0 to 65535) is divided into three categories.

0 - 1023 Well-Known Ports The numbers are reserved by IANA for system processes or network programs with administrative rights. Ports from this category should not be used without registering with IANA.

1024 - 49151 Registered Ports Ports registered for use by conventional programs and application layer protocols. This category of ports is most popular for commercial software. Registration is also required to use any port.

49152 - 65535 Dynamic ports Designed for free but temporary use. Registration of ports in this category is not possible.

Our Port checker tool allows you to test open ports in your system. You can easily verify if any port is opened or not not by typing your IP address or domain name and desired port number.

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

When I connect to https://www.google.co.uk this changes to 216.58.198.228:443. 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 forcing it to be 63999.

9 is there a way of forcing it to be 63999 Do you have any reason for trying to do this? – A.L Aug 29, 2016 at 11:52
1 If you're writing an application, you can open any (unused) source port that you want. But it's not a good idea and not clear why you want this? – pjc50 Aug 29, 2016 at 13:08
6 @pjc50 Indeed, this question seems like it might be having an XY problem . – Dev Aug 29, 2016 at 16:27
1 I"ve submitted an edit to change the title to say "source" rather than "local", as destination port numbers are "local" to the destination machine, but the source of the initial TCP SYN packet is unambiguously that of the initiator of the connection. – Monty Harder Aug 29, 2016 at 18:50

3 Answers 3

How are local ports determined.

The port number is chosen by the TCP implementation software from a range of port numbers called Ephemeral Ports .

The exact mechanism for choosing the port number and the range to be used is Operating System dependent.

Is there a way of forcing it to be 63999.

This can be done by changing the configuration of the TCP implementation software.

Instructions on configuring the Ephemeral Ports range for a variety of different Operating Systems can be found at Changing the Ephemeral Port Range .

Instructions for Linux and Windows are included in this answer below for reference.

However, it is not a good idea to restrict the range to a single port, for example 63999 .

In fact on Windows this is not possible as:

The minimum range of ports that can be set is 255.

The Ephemeral Port Range

A TCP/IPv4 connection consists of two endpoints, and each endpoint consists of an IP address and a port number. Therefore, when a client user connects to a server computer, an established connection can be thought of as the 4-tuple of (server IP, server port, client IP, client port). Usually three of the four are readily known -- client machine uses its own IP address and when connecting to a remote service, the server machine's IP address and service port number are required. What is not immediately evident is that when a connection is established that the client side of the connection uses a port number. Unless a client program explicitly requests a specific port number, the port number used is an ephemeral port number. Ephemeral ports are temporary ports assigned by a machine's IP stack, and are assigned from a designated range of ports for this purpose. When the connection terminates, the ephemeral port is available for reuse, although most IP stacks won't reuse that port number until the entire pool of ephemeral ports have been used. So, if the client program reconnects, it will be assigned a different ephemeral port number for its side of the new connection.

Source The Ephemeral Port Range

Changing the Ephemeral Port Range

Linux allows you to view and change the ephemeral port range by simply using the file /proc/sys/net/ipv4/ip_local_port_range . For example, this shows the default configuration on a kernel 2.2 system: $ cat /proc/sys/net/ipv4/ip_local_port_range 1024 4999 To change this to the preferred range, you could do (as superuser): # echo "49152 65535" > /proc/sys/net/ipv4/ip_local_port_range Note that you would need to do this each time the system boots, so be sure to add a line to a system startup script such as /etc/rc.local so your range is always used. Also note that the Linux 2.4 kernel will default the range of 32768 through 61000 if adequate kernel memory is available, so changing the range may not be necessary on newer Linux systems. Finally, also note that you may be able to use the sysctl interface to change the settings rather than using the /proc filesystem. The name of the sysctl parameter is "net.ipv4.ip_local_port_range". Edit the /etc/sysctl.conf file if you have it, or have a startup script run the sysctl command manually if you want to change this parameter using sysctl .

Windows Vista/Windows Server 2008 and newer:

As of Windows Vista and Windows Server 2008, Windows now uses a large range (49152-65535) by default, according to Microsoft Knowledgebase Article 929851 . That same article also shows how you can change the range if desired, but the default range is now sufficient for most servers.

Source Changing the Ephemeral Port Range

You can view the dynamic port range on a computer that is running Windows Vista or Windows Server 2008 computer by using the following netsh commands: netsh int ipv4 show dynamicport tcp netsh int ipv4 show dynamicport udp netsh int ipv6 show dynamicport tcp netsh int ipv6 show dynamicport udp Notes: The range is set separately for each transport and for each version of IP. The port range is now truly a range with a starting point and with an endpoint. Microsoft customers who deploy servers that are running Windows Server 2008 may have problems with RPC communication between servers if firewalls are used on the internal network. In these cases, we recommend that you reconfigure the firewalls to allow for traffic between servers in the dynamic port range of 49152 through 65535 . This range is in addition to well-known ports that are used by services and by applications. Or, the port range that is used by the servers can be modified on each server. You adjust this range by using the netsh command, as follows: netsh int <ipv4|ipv6> set dynamic <tcp|udp> start=number num=range This command sets the dynamic port range for TCP. The start port is number, and the total number of ports is range. The following are sample commands: netsh int ipv4 set dynamicport tcp start=10000 num=1000 netsh int ipv4 set dynamicport udp start=10000 num=1000 netsh int ipv6 set dynamicport tcp start=10000 num=1000 netsh int ipv6 set dynamicport udp start=10000 num=1000 These sample commands set the dynamic port range to start at port 10000 and to end at port 10999 (1000 ports). Notes: The minimum range of ports that can be set is 255 . The minimum starting port that can be set is 1025 . The maximum end port (based on the range being configured) cannot exceed 65535 . To duplicate the default behavior of Windows Server 2003, use 1025 as the start port, and then use 3976 as the range for both TCP and UDP. This results in a start port of 1025 and an end port of 5000 .

Source Microsoft Knowledgebase Article 929851 :

Windows XP and older:

For older Windows operating systems (Windows XP and older), Windows uses the traditional BSD range of 1024 through 4999 for its ephemeral port range. Unfortunately it appears that you can only set the upper bound of the ephemeral port range. Here is information excerpted from Microsoft Knowledgebase Article 196271 : Start Registry Editor ( Regedt32.exe ). Locate the following key in the registry: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters On the "Edit" menu, click "Add Value", and then add the following registry value: Value Name: MaxUserPort Data Type: REG_DWORD Value: 65534 (for example) Valid Range: 5000-65534 (decimal) Default: 0x1388 (5000 decimal) Description: This parameter controls the maximum port number used when an application requests any available user port from the system. Normally, ephemeral (that is, short-lived) ports are allocated between the values of 1024 and 5000 inclusive. Quit Registry Editor. Note: There is another relevant KB article ( 812873 ) which claims to allow you to set an exclusion range, which could mean that you could exclude ports 1024-9999 (for example) to have the ephemeral port range be 10000-65534 . However, we have not been able to get this to work (as of October 2004).

1 For at least windows is seems like it is possible to restrict the port range system wide. In most cases this is probably a bad idea, especially restricting it to one port would be: See KB 929851 , the commands listed at least work on Windows 7. – Seth Aug 29, 2016 at 10:36
@Seth Yes. I was reluctant to mention this since the OP didn't mention his OS and I didn't want to expand the answer to cover N operating systems ... – DavidPostill ♦ Aug 29, 2016 at 10:38
You're right about that. After all there are plenty of operating systems. It's just something I stumbled across while originally trying to answer this question. As your answer was up faster I just thought I'd add it. It's a really well written answer! :) Just added it as a hint that sometimes changing the configuration is sufficient rather than reprogramming (maybe my understanding is just different - for me that sounds akin to recompile). – Seth Aug 29, 2016 at 10:45
1 In fact, in Linux too it is very simple: just do echo "49152 65535" > /proc/sys/net/ipv4/ip_local_port_range . It is so simple that it can be done on a per-command basis. – MariusMatutiae Aug 29, 2016 at 11:06
2 Rather than changing the ephemeral port range it would be much better to have the application call the bind system call before it calls connect . Some applications have an option to do that, other applications do not. – kasperd Aug 29, 2016 at 19:24

David Postill's answer is perfectly right. I would like just to add to it, by stressing that changing the ephemeral port range in Linux is so simple, that the OP has an affirmative answer.

You change the EPR as follows:

and you can select port 50000 (as an example) with the following script:

One caveat here: since there is a single port in the range, another application might snatch it away from you between the execution of the third and the fourth lines above; also, even if there is no race condition, you will paralyze all other applications until you restore a large EPR, which is why I restored the original range as soon as possible.

Thus, if the OPs' operating system had been Linux, the answer would have been that it could easily be done.

Amazingly, this is not as straightforward on BSDs, some of which do not even have a runtime kernel setting for the EPR. MacOS X, FreeBSD and OpenBSD require modifying the file /etc/sysctl.conf , but they have different choices for the EPR.

Regardless of the above and of the OS, the fact that something can be done does not mean it ought to be done: why on Earth do you need this? I cannot think of a single use case.

For Linux example +1. – DavidPostill ♦ Aug 29, 2016 at 11:38
Hehe. BSD/OS requires recompiling the kernel :) – DavidPostill ♦ Aug 29, 2016 at 11:54
1 @DavidPostill That's a major bummer. – MariusMatutiae Aug 29, 2016 at 12:00
There is a flaw in your code example. Your type cast is very misplaced. Additionally it would be a good idea to make BIND_PORT optional, such that the code still can be used in exactly the same way as the original. I think htons(bind_port_env ? atoi(bind_port_env) : 0) would do the right thing. – kasperd Aug 30, 2016 at 19:11
Um, isn't this code firing up the application and restoring the old range in parallel? (That might not work too well :-) And there's a quote missing. – debater Feb 13 at 1:42

It's worth adding that Linux kernel also has

net.ipv4.ip_local_reserved_ports

knob that does somewhat opposite but nevertheless it might be very useful because that way you can "punch a hole" for services that open specific port(s) in otherwise ephemeral range of ports.

Brief excerpt from the docs :

Specify the ports which are reserved for known third-party applications. These ports will not be used by automatic port assignments (e.g. when calling connect() or bind() with port number 0). Explicit port allocation behavior is unchanged. The format used for both input and output is a comma separated list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 10). Writing to the file will clear all previously reserved ports and update the current list with the one given in the input.

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How to Set Up Port Forwarding

Some games and programs only work if you open a specific port

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How Do You Set Up Port Forwarding?

Give Device a Static IP Address

Set Up Port Forwarding

Extra: More Open Port Tips
Frequently Asked Questions

Specific ports must be open on your router for some video games and programs to work properly. Although the router has some ports open by default, most are closed and only usable if you manually open these ports. When your online video games, file server, or other networking programs don't work, access the router and open the specific ports that the application needs.

Maddy Price / Lifewire

The traffic that passes through your router does so through ports. Every port is like a special pipe made for a specific kind of traffic. When you open a port on a router, it allows a particular data type to move through the router.

The act of opening a port, and choosing a device on the network to forward those requests to, is called port forwarding. Port forwarding is like attaching a pipe from the router to the device that needs to use the port—there's a direct line-of-sight between the two that allows data flow.

For example, FTP servers listen for incoming connections on port 21 . If you have an FTP server set up that nobody outside your network can connect to, open port 21 on the router and forward it to the computer you use as the server. When you do this, that new, dedicated pipe moves files from the server, through the router, and out of the network to the FTP client that's communicating with it.

The same is true for other scenarios like video games that need the internet to communicate with other players, torrent clients that require specific ports to be open for uploading files, and instant messaging applications that only send and receive messages through a specific port.

Every networking application needs a port to run on, so if a program or application isn't working when everything else is set up correctly, open the port on the router and forward requests to the right device (for example, a computer, printer, or game console).

Port range forwarding is similar to port forwarding but is used to forward an entire range of ports. A certain video game might use ports 3478 through 3480, for example, so instead of typing all three into the router as separate port forwards, forward that whole range to the computer running that game.

Below are two primary steps you need to complete to forward ports on a router. Because every device is different, and because there are many router variations, these steps are not specific to any device. If you need additional help, refer to the user manual for the device, for example, the user guide for your router.

Give the Device a Static IP Address

The device that will benefit from the port forward needs to have a static IP address . This way, you don't have to change the port forwarding settings each time it obtains a new IP address.

For example, if your computer runs torrenting software, assign a static IP address to that computer. If your gaming console uses a specific range of ports, it needs a static IP address.

There are two ways to do this: from the router and from the computer. When you set up a static IP address for your computer, it's easier to do it there.

Use Your Computer to Set Up a Static IP Address

To set up a Windows computer to use a static IP address, first identify which IP address it's using currently.

Open Command Prompt on the computer.

Type this command, then select Enter :

Record the following: IPv4 Address , Subnet Mask , Default Gateway , and DNS Servers .

If you see more than one IPv4 Address entry, look for the one under a heading like Ethernet adapter Local Area Connection, Ethernet adapter Ethernet, or Ethernet LAN adapter Wi-Fi. Ignore anything else, like Bluetooth, VMware, VirtualBox, and other non-default entries.

Now, you can use that information to set up the static IP address.

Open the Run dialog box with the WIN + R keyboard shortcut, enter ncpa.cpl , and select OK to open Network Connections.

Right-click or tap-and-hold the connection that has the same name as the one you identified in Command Prompt. For example, Ethernet0 .

Select Properties from the menu.

Choose Internet Protocol Version 4 (TCP/IPv4) from the list, then select Properties .

Select Use the following IP address .

Enter the details you copied from Command Prompt: IP address, subnet mask, default gateway, and DNS servers.

Choose OK when you're done.

If you have several devices on your network that get IP addresses from DHCP , don't reserve the same IP address you found in Command Prompt. For example, if DHCP is set up to serve addresses from a pool between 192.168.1.2 and 192.168.1.20, configure the IP address to use a static IP address that falls outside that range to avoid address conflicts . For example, use 192.168.1. 21 or above. If you're not sure what this means, add 10 or 20 to the last digit in your IP address and use that as the static IP in Windows.

You can also set up a Mac to use a static IP address , as well as Ubuntu and other Linux distributions.

Use Your Router to Set Up a Static IP Address

Another option is to use the router to set up a static IP address. Do this when a non-computer device needs an unchanging address (like a gaming console or a printer).

Access the router as admin .

Locate a Client List, DHCP Pool, DHCP Reservation, or similar section of the settings. The section lists the devices currently connected to the router. The IP address of the device is listed along with its name.

Look for a way to reserve one of those IP addresses to tie it with that device so that the router always uses it when the device requests an IP address. You might need to select the IP address from a list or choose Add or Reserve .

The above steps are generic since static IP address assignment is different for each router, printer, and gaming device. Instructions differ if you need to reserve IP addresses for NETGEAR routers , edit DHCP settings on Google devices, or configure DHCP reservation on Linksys routers .

To make your public IP address static so that you can access your devices from an outside network, pay for a static IP. A workaround involving setting up a dynamic DNS service is just as helpful.

Now that you know the device's IP address and configured it to stop changing, access the router and set up the port forwarding settings.

Locate the port forwarding options. These are different for every router but might be called something like Port Forwarding, Port Triggering, Applications & Gaming, or Port Range Forwarding. These might be buried within other categories of settings like Network, Wireless, or Advanced.

Type the port number or port range that you want to forward. If you're forwarding one port, type the same number under both the Internal and External boxes. For port ranges, use the Start and End boxes.

Most games and programs indicate which ports must be open on the router. If you don't know what numbers to type here, PortForward.com has a list of common ports.

Choose a protocol, either TCP or UDP ports . Choose both, if needed. This information should be available from the program or game that explains the port number.

Type the static IP address you chose.

If asked, name the port trigger anything that makes sense to you. If it's for an FTP program, call it FTP . Call it Medal of Honor if you need the port open for that game.

Enable the port forwarding rule with an Enable or On option.

Here's an example of what it looks like to forward ports on a Linksys WRT610N:

Some routers have a port forward setup wizard that makes it easier to configure. For example, the router might first give you a list of devices already using a static IP address and then let you choose the protocol and port number from there.

More port forwarding instructions:

D-Link port forwarding
Belkin port forwarding
Google Nest Wi-Fi or Google Wi-Fi port forwarding

More on Open Ports

If forwarding a port on your router doesn't allow the program or game to work on your computer, find out if a firewall program blocked the port. The same port needs to be open on the router and your computer for the application to use it.

To see if the Windows Firewall is blocking a port that you opened on the router, temporarily disable the firewall and then test the port again. If the port is closed on the firewall, edit some firewall settings to open it .

When you open a port on the router, traffic can flow in and out of it. When you scan the network for open ports, you should see everything that's open from the outside. There are websites and tools build specifically for this.

Here are some reasons why you would check for open ports:

To avoid getting into the router to check.
To make sure the port opened correctly when a program or game isn't working.
To make sure a port you closed is actually closed.

Several places offer a free open port checker. PortChecker.co and NetworkAppers have online port checkers that scan a network from the outside. Another option is to download Advanced Port Scanner or FreePortScanner to scan devices within your private network.

Only one port forward can exist for every instance of that port. For example, if you forward port 3389 (used by the Remote Desktop remote access program) to a computer with the IP address 192.168.1.115, that same router can't also forward port 3389 to 192.168.1.120.

In cases like this, the only solution, if possible, is to change the port the program uses. This may be possible from the software settings or through a registry hack. In the RDP example, if you edit the Windows Registry on the 192.168.1.120 computer to force Remote Desktop to use a different port like 3390, you could set up a new port forward for that port and use Remote Desktop on two computers within the same network.

Log in to your router and navigate to its port forwarding section. Enter your computer or gaming console's IP address and Minecraft's TCP and UDP ports. Minecraft on a PC uses 25565 (TCP) and 19132-19133, 25565 (UDP).

Go to Settings > Network > Advanced Settings and note your console's IP address. Log in to your router and enter the console's IP address. On your console, go to Settings > Network > Test Network Connection and follow the connection prompts. Go to your router's port forwarding tools and open 88, 500, 3544, 4500 (for UDP), and 3074 (TCP). Go back to Settings > Network and select Test NAT type .

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For this system to work well, universal agreement on port assignments is essential. Thus, this becomes another situation where a central authority is needed to manage a list of port assignments that everyone uses. For TCP/IP, it is the same authority responsible for the assignment and coordination of other centrally-managed numbers, including IP addresses, IP Protocol numbers and so forth: the Internet Assigned Numbers Authority (IANA) .

As we have seen, there are 65,536 port numbers that can be used for processes. But there are also a fairly large number of TCP/IP applications, and the list grows every year. IANA needs to carefully manage the port number “address space” to ensure that port numbers are not wasted on protocols that won't be widely used, while also providing flexibility for organizations that need to make use of obscure applications. To this end, the full spectrum of TCP and UDP port numbers is divided into three ranges, as shown in Table 144 .:

The existence of these ranges ensures that there will be universal agreement on how to access a server process for the most common TCP/IP protocols, while also allowing flexibility for special applications. Most of the TCP/IP applications and application protocols use numbers in the well-known port number range for their servers. These port numbers are not generally used for client processes, but there are some exceptions. For example, port 68 is reserved for a client using the Boostratp Protocol (BOOTP) or Dynamic Host Configuration Protocol (DHCP) .

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The default dynamic port range for TCP/IP has changed since Windows Vista and in Windows Server 2008

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This article describes the changes to the default dynamic port range for TCP/IP in Windows Vista and in Windows Server 2008.

Support for Windows Vista without any service packs installed ended on April 13, 2010. To continue receiving security updates for Windows, make sure that you are running Windows Vista with Service Pack 2 (SP2). For more information, go to the following Microsoft website: Support is ending for some versions of Windows

Applies to: Windows Server 2019, Windows Server 2016, Windows Server 2012 R2, Windows 10 - all editions Original KB number: 929851

Introduction

To comply with Internet Assigned Numbers Authority (IANA) recommendations, Microsoft has increased the dynamic client port range for outgoing connections in Windows Vista and Windows Server 2008. The new default start port is 49152, and the new default end port is 65535. This is a change from the configuration of earlier versions of Windows that used a default port range of 1025 through 5000.

More Information

You can view the dynamic port range on a computer that is running Windows Vista or Windows Server 2008 by using the following netsh commands:

netsh int ipv4 show dynamicport tcp
netsh int ipv4 show dynamicport udp
netsh int ipv6 show dynamicport tcp
netsh int ipv6 show dynamicport udp

The range is set separately for each transport (TCP or UDP). The port range is now truly a range that has a starting point and an ending point. Microsoft customers who deploy servers that are running Windows Server 2008 may have problems that affect RPC communication between servers if firewalls are used on the internal network. In these situations, we recommend that you reconfigure the firewalls to allow traffic between servers in the dynamic port range of 49152 through 65535. This range is in addition to well-known ports that are used by services and applications. Or, the port range that is used by the servers can be modified on each server. You adjust this range by using the netsh command, as follows: netsh int <ipv4|ipv6> set dynamic <tcp|udp> start= number num= range . This command sets the dynamic port range for TCP. The start port is number , and the total number of ports is range .

The following are sample commands:

netsh int ipv4 set dynamicport tcp start=10000 num=1000
netsh int ipv4 set dynamicport udp start=10000 num=1000
netsh int ipv6 set dynamicport tcp start=10000 num=1000
netsh int ipv6 set dynamicport udp start=10000 num=1000

These sample commands set the dynamic port range to start at port 10000 and to end at port 10999 (1000 ports). The minimum range of ports that can be set is 255. The minimum start port that can be set is 1025. The maximum end port (based on the range being configured) cannot exceed 65535. To duplicate the default behavior of Windows Server 2003, use 1025 as the start port, and then use 3976 as the range for both TCP and UDP. This results in a start port of 1025 and an end port of 5000.

When you install Microsoft Exchange Server 2007 on a Windows Server 2008-based computer, the default port range is 1025 through 60000.

For more information about security in Microsoft Exchange 2007, go to the following Microsoft TechNet website: Exchange 2007 Security Guide

For more information about IANA port-assignment standards, go to the following IANA website: Service Name and Transport Protocol Port Number Registry

Microsoft provides third-party contact information to help you find technical support. This contact information may change without notice. Microsoft does not guarantee the accuracy of this third-party contact information.

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If Network Director fails to read the configuration of one or more devices after the device discovery, such devices are not displayed in the Assignments list. You will not be able to assign profiles to such devices. The Manage Jobs page in System mode displays details of the device discovery jobs. Use the information displayed on this page to take appropriate corrective steps to enable Network Director to reread the configuration of the failed device. For more information, see Discovering Devices in a Physical Network .

The Assign Profile to Ports window opens.

Select either Ports (default) or Port Range . If you selected multiple devices in the previous step, you cannot choose the Port option.

By default, aggregated Ethernet interfaces are listed after the ge- and xe- interfaces in the list of ports. Members of aggregated Ethernet interfaces are not included in the port list.

In the Normal Ports section, enter a first and last port name in the text boxes, then click Add The port range appears in the Selected Port Range section.
Repeat the add process to add any additional port ranges.
To delete a port range, select its check box, then click Delete

At least one port within the port range must be available on each selected device for the port range to succeed. Channelized ports are supported in a port range. Assignments are created for the ports within the port range that are available. You can assign the profile to the same interface on multiple devices by entering the interface name in both fields of the port range.

The port assignment appears in the list of Assignments, with the Device, Type, Assigned To, and Attributes columns completed. In the Attributes column, you see a triangle and the link Define .

If the Port profile is a switching profile that contains an Authentication profile—in other words, the profile is enabling 802.1X authentication on ports—click the Define link in the Attributes column for a device to define additional authentication attributes.

The Configure attributes window opens. Fill in the fields described in Table 1 .

If you see the message Port profile does not have an associated Authentication profile. Please configure the Authentication profile. ;then click OK , and edit the Port profile by selecting Port under Profile and Configuration Management, selecting the Port profile from the list and clicking Edit . The Authentication profile association is located in the Port Family Options section.

The attributes you define for the device apply to all 802.1X authenticator interfaces on the switch. Different sets of interfaces on the switch cannot have different attributes.

If the Port profile is a routing profile, click the Define link in the port’s Attributes field to configure an IPv4 or IPv6 address on the interface.

Repeat this step for all the ports on which you want to configure IPv4 or IPv6 interfaces.

For review directions, see Reviewing and Accepting the Assignments .

Use the Review step of the Assign Port Profile wizard to review and accept your assignments:

Click Edit to return to the Profile Assignment step and make changes to your assignments.

Click Finish to accept the assignments.

After you click Finish, the Create Profile Assignments Job Details window opens, which reports on the status of the profile assignment job. If you have assigned the profile to a large number of objects, the profile assignment job can take some time to complete. Instead of waiting for the Job Details window to report job completion status, you can close it and check the details of the profile assignment job at a later time by using the Manage Job task in System mode.

If any assignment fails, the profile assignment job fails and none of the assignments are created. Check the details for the profile assignment job for information about why the assignment failed.

After the profile assignment job completes, you can deploy the configuration defined in the Port profile and in the port-specific and device-specific attributes on the affected devices. See Deploying Configuration to Devices .

Use the Edit Assignments page to change Port profile assignments. You can:

Delete a port from the profile assignments.

If the profile has been already deployed on the port, then the configuration is removed from the port when you next deploy the configuration on the device. The configuration removed includes any port configuration that was defined in associated profiles, such as the CoS, Authentication, and IPv4 or IPv6 Filter profiles.

Change the IPv4 or IPv6 address for ports associated with a routing Port profile.

Change the device-specific authentication attributes, such as the Access profile associated with the device. For more information about these attributes, see Table 1 .

You cannot assign the Port profile to additional ports by using the Edit Assignment page. To add port assignments, use the Assign Port Profile wizard.

Table 2 describes the fields in the Edit Assignments page and how to use them to change the profile assignments. When you are finished with your modifications, click Apply . You can then deploy your modifications on the affected devices.

Starting Network Director Release 3.5, you can unassign multiple port profiles that are assigned to multiple ports, at the same time.

To unassign port profiles:

On the Network Director banner, under Views , select one of the following views—Logical View, Location View, Device View, or Custom Group.

The Manage Port Profile page appears.

A confirmation message indicating the profiles were successfully unassigned appears and the status of the profiles change to Pending Deployment.