What's the difference between proxy and firewall?

Question

What's the difference between proxy and firewall? And can we integrate a nat or pat into a proxy or firewall?

Answer 1

A Proxy Server is a device that:

acts as an intermediary for requests from clients seeking resources from other servers.

A Firewall is a device that is:

designed to permit or deny network transmissions based upon a set of rules

The former just lets all traffic through regardless of source or destination and is a way of routing requests through known gateways and is often used to allow companies to log network traffic for example.

A proxy may include a firewall as part of it's functionality but it doesn't have to.

I would expect that Network Address Translation (NAT) and Port Address Translation (PAT) - which is basically the same thing - would be functionality that could be built in, but NAPT is more used on routers etc. to:

However it is common to hide an entire IP address space, usually consisting of private IP addresses, behind a single IP address (or in some cases a small group of IP addresses) in another (usually public) address space.

Answer 2

And can we integrate a nat or pat into a proxy or firewall?

Yes, Microsoft's Threat Management Gateway (TMG) is an example of a proxy & firewall wrapped into one.

Answer 3

Proxies are used explicitly, for example a browser is configured to forward http requests to a proxy. A firewall is used implicitly, for example to drop some network connections. NAT works at the network level. NAT uses the same mechanisms as a stateful firewall to let a few machines appear with a single external IP address. Conceptually that makes NAT closer to a firewall. On the other hand the fact that a NAT rewrites packets (changing ports and addresses) is similar to a proxy changing ports and addresses and adjusting headers before relaying a request.