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TCP/IP packets are what keep the internet running. If you are up to speed with your networking knowledge, then you’d know that all the information on the internet flows in the form of TCP/IP packets (bit-sized data segments) and the way a midway router or destination system recognizes and differentiates these packets is through the port numbers their headers contain, among other things.
If you want to learn more about the differences between local ports and remote ports and how to infer what they do, in addition to their use in networking tools such as firewall setup or SQL server whitelisting, then keep reading for exactly that.
What Is Local Port And Remote Port
As mentioned earlier, the TCP/UDP packets have a marker on them in the form of a source, and destination port value pair, but what exactly are these ports, and where is their destination? In networking terminology, ports are software-defined outlets through which a network protocol sends and receives data.
They are designed so that a computer can discern what data packet is meant for which process, as each will be bound to a specific port. That is why you might have noticed that computers have upwards of a thousand network ports in them to account for all the processes.
Local port means the source port that a TCP/UCP packet uses. This will be the port through which a specific program running on your computer will request and respond to network traffic.
As an example, if you have two instances of a web browser tab open, both using different ports, and you block one of the ports in your firewall software, then that tab will stop responding while the other one will function normally.
The remote port is the other part of this puzzle. It is labeled as the destination port in a network packet header. This is going to be the port that your network traffic will be sent to on the client/receiving computer.
Differences Between Local Port vs Remote Port
With the basic definitions set aside, let’s dig into what are the differences between these two types of ports. While in terms of software implementation, they might seem to be the one and the same, logistically speaking, there are certain traits that set them apart.
First and foremost – and this is something we touched upon in the definitions section – is the fact that they originate from different devices. In any network layer communication protocol, there is always a sender and a receiver.
The port number that the sender has is known as the local port or the source port because the data sent over the internet is sourced or localized from here. The port number that the receiver has is known as the remote port or the destination port, as it is the destination port of the traveling data packet.
Port Selection Control
With the fact that the sender owns the local port established, we can move on to port selection and overall control over port behaviors. The local port an application ends up using is something that the user themselves can control.
For example, when setting up a SQL server, you can configure it to use a specific port, assuming it’s always available. On the other hand, the remote port is something the remote server/machine has control over.
Every time you make a request to a server, it might bind your new connection to a new port as it dynamically appoints port numbers to new incoming requests. So, as an example, you cannot define a firewall rule regarding which remote port numbers are allowed or disallowed, as you cannot know beforehand which one you will be assigned.
To wrap up all of our discussion, the remote port is the port number that the machine, on the other hand, of a connection has, while the local port is what the sender of the request/data has. You might also come across them labeled destination port and source port, respectively.
To see a more diagrammatic overview of our discussion, see the accompanying table below.
|Local Port||Remote Port|
|Source||On the sender's end of the TCP/IP connection.||On the receiver's end of the TCP/IP connection.|
|Port Selection Control||The sender or connection initiator has control.||The sender or connection initiator has no control.|
After reading through this detailed article, you should be well versed in the ports terminology used in the networking space. For more brief and detailed articles and guides such as this, explore our website catalog, and you will be sure to find something relevant.