#of DNS Servers

[Simon Waters]

Tony wrote:
> 
> We are running our own Internal DNS servers both MS DNS and bind. Also
> have our ISPs DNS servers. Question is will performance in name
> resolution be affected as far as resolving internet domains names if
> we have 3 to 4 internal DNS servers listed first in the DHCP
> configuration?
> 
> eg. 192.168.0.20 -- primary internal DNS
>     192.168.0.21 -- secondary internal DNS
>     24.20.31.219 -- primary ISP DNS
>     24.20.31.220 -- secondary ISP DNS
> 
> I mean how many internal DNS server addresses can i list before name
> resolution to the internet will be affected?

Do your internal DNS servers and the ISP DNS servers provide
an identical view of the DNS? 

i.e. Do the Internal servers provide any information not
available on the public Internet? If yes you probably don't
want to list the ISP servers at all in the DHCP settings,
rather you want your internal DNS servers to handle all
queries.

Whilst in a Microsoft only world all DNS servers would be
queried eventually (1 second delay per server or some such),
not everything in the world is a Microsoft OS, and better
performance and easier management comes from doing things
the way the standards committees imagined it. Some Microsoft
OSes normally only have 3 DNS servers configured maximum, so
I'm not sure what they do if you give them 4 or more via
DHCP.