DNS lookup and HTTP proxies

Question

How are DNS lookups managed when using a proxy ? I tried to nslookup google.com and it is unable to find it from my local DNS so what is the path of DNS lookups with a simple HTTP proxy ?

Solution

It depends on what type of HTTP proxy and protocol you're using.

In most cases you're likely to encounter the web browser will pass the fully-qualified domain name to the HTTP proxy, which will perform the DNS lookup and forward the request (and potentially take other actions).

However, there are cases where your web browser will have to do its own DNS lookup. These include certain proxy types (e.g. "SOCKS 4") or where the hostname is on your browsers "bypass the proxy" list.

You system administrators may have configured your machine to do all DNS lookups via a proxy. There are a number of reasons for this: to minimize organizational DNS requests, to monitor all the DNS lookups in the organisation more easily, to route certain DNS queries as they see fit. If this is the case they will probably have removed DNS lookup abilities from your machine.