For Enableing UPNP ( Universal Plug and Play) In Arris Router/Modem First we just need to access Router Page of the Router That is also known as Default Gateway.
How to know what is default Gateway of any network-
Now open the web browser and type the default gateway IP address In Address bar and hit enter.
Then type the username and passward (default will be ''Username – admin” , “Password – password”)
Note : -Basically in Arris Router/modem they have two types of setting to enable UPnP on Arris router.
1 - Advanced > Device Discovery
2 . IN Wireless MENU