Citando o Projeto de Documentação do Linux ,
Etapa 1: Quais serviços são realmente necessários ?
BIND (named) - This often is installed by default, but is only really needed if you are an authoritative name server for a domain. If you are not sure what this means, then you definitely don't need it.
BIND is probably the number one crack target on the Internet.
BIND is often used though in a "caching" only mode.
This can be quite useful, but does not require full exposure to the Internet.
In other words, it should be restricted or firewalled.
E, se você realmente quiser usar um DNS em cache , Eu acho que BIND 9
também deve ser verificado.