How do i restrict Internet access to some sites

General Topics
1

Hello all, I configured my server to work as a DHCP server. My question is how can I manage or restrict the other computer Internet access like blocking youtube, blocking social media, and other sites and allow only some limited sites?

2

Google is your friend

https://www.google.no/search?source=hp&ei=goBPYKPJAdTFgwfKu46AAQ&iflsig=AINFCbYAAAAAYE-OkqA21tzfeEDrp1I8RJJu9BYA4t9E&q=how+to+block+websites+when+using+dhcp+server&oq=how+to+block+websites+when+using+dhcp+server&gs_lcp=Cgdnd3Mtd2l6EAMyBggAEBYQHjoICAAQsQMQgwE6DggAELEDEIMBEMcBEKMCOgUIABCxAzoICAAQxwEQrwE6DggAELEDEIMBEMcBEK8BOgIILjoCCAA6BQguEJMCOggILhCxAxCDAToFCC4QsQM6BAgAEBM6CAgAEBYQChAeOggIIRAWEB0QHlC3CFiWggFg4oQBaABwAHgAgAHqAogBniGSAQkzMi4xMS4wLjGYAQCgAQGqAQdnd3Mtd2l6&sclient=gws-wiz&ved=0ahUKEwijkoDV0bLvAhXU4uAKHcqdAxAQ4dUDCAY&uact=5

3

did this but do not find any relative solution, I am using Ubuntu 16.04

4

So, how is this related to Avast…!? Best you post/ask in Ubuntu forum.