Problem with the internent connection

[siva2]

Unfortunately, I dont speak German and I was unable to reach a Customer Support technician who can help me inn English.

I have strange issue .I am using Vf DSL cable . I could able to open all websites on my laptop and mobile using Wifi.

When My friend try to connect the network the Wifi signle is not showing and tried to connect using manual set up which doesn't work.
Using LAN my friend able to connect the laptop and only You tube he coudl able to open and play it . 

Some other website he could not able to open and after 2 to 3 mins he will get a  error message .

the same website he coudl able to open by his mobiel wifi (using vodaphone) teh website are loading .

I am really not sure what  is teh cause of this issue. Do I need to make any changes on router settings?

Edit: In korrektes Forum verschoben. 

[Andre]

Hey Siva2,

what tariff are you using excactly?
Either its DSL (for example gigazuhause 100 DSL) - where the router is directly connected with the telephone connection socket.
Or its internet via cable (for example gigazuhause 100 cable) - the modem is connected with the multimedia / tv socket.

If only some pages are acessible , this sounds like a issue with the name resolving of websites / dns.

Since its working flawlessly on all your devices , but not his , i feel like he has set up some kind of proxy / different dns service for the connection with the router.