A user purchased a retail router and would like to set up a private network.

For setting up a private network, the IP address range should be one that is reserved for private use. The range 172.16.0.0 to 172.31.255.255 falls within the set of IP addresses designated for private networks according to RFC 1918. This range is not routable on the public internet, making it ideal for a private network setup on a retail router.