Como altero os endereços DNS em um BT Homehub 3?
Infelizmente você não pode. A BT bloqueou o DNS nos seus dispositivos Homehub.
BT lock the DNS server settings in firmware to prevent programs from changing the settings, and directing people to rogue DNS servers.
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There were vunerabilities with the early home hubs which allowed scripts to change the DNS settings.
BT also like to make life easier for the helpdesk, and stopping alterations to the home hub reduces the likelihood of problems.
There is a list of routers which can be used on ADSL and Infinity here.
Replacements for BT home hub 3 - this link is only accessible from a BT network ("Sorry, you can only access this site from a BT broadband connection.")
Fonte Alterando o servidor DNS padrão
Most routers should let you alter the default DNS server addresses through their configuration page. This will affect every device that uses it to connect to the internet, making it the easiest way to change DNS servers if you have more than one internet-enabled device in the home. Unfortunately for BT Broadband customers, this isn't possible on a BT Home Hub.
Fonte Como corrigir problemas de DNS da BT usando o DNS do Google