UPnP is enabled by default. It allows devices on your network to communicate with less friction, both with the internet and with other devices on your local network.
UPnP and your network
Within your local network, UPnP lets your devices discover each other more easily. For example, you might want to print a picture from a computer. If your computer and printer are on the same network, and you leave UPnP on, it would let them automatically find and communicate with each other.
Similarly, UPnP is often used for local network video streaming between devices. Chromecast, for example, can use UPnP to better communicate with your TV and gaming consoles, and digital cameras often use UPnP, too.
UPnP also allows devices to request more direct access to the internet by asking the router to open a specific port.
UPnP and the internet
UPnP lets devices request that specific communication ports be opened between themselves and the internet. For example, a gaming console might use port 3074 to communicate with online gaming servers. Instead of configuring that port yourself, UPnP lets the console ask the router to open it for you.
The trade off is that you don't know which devices or applications have asked for open ports. An open port is like a new entry point into your network, so it’s undesirable from a security standpoint to have several open ports. If you want total control over which ports are open, you can turn off UPnP and manually configure port forwarding rules.
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