[X4U] What is NAT and what does it mean to me?

[Eugene]

On Thu, May 10, 2007 at 05:37:56PM CDT, Robert Ameeti <robert at ameeti.net> wrote:
: 
: At 3:21 PM -0700, 5/10/07, Eddie Hargreaves wrote:
: 
: > NAT is Network Address Translation
: >
: > Your ISP provides you with a single IP address, like 67.181.33.253 and if
: > you want to hook up multiple devices to the Internet through that one
: > connection, you use a router which provides those devices with different IP
: > addresses like 10.0.1.2 and 10.0.1.3. That is NAT.
: 
: Nope, That is DHCP. (Dynamic Host Configuration Protocol)

Specifically, DHCP does the automagic IP address assignment.

: > When two devices on the same network try and distribute IP addresses using 
: > NAT, it can cause problems.
: 
: If you are describing double NAT, then the above would not be addressing the 
: issue.
: 
: Double NAT would be where the ISP's router was doing NAT and providing a 
: 'network' of addresses and then one of the devices (your AirPort) hooked up 
: to one of its ports was also doing NAT. It is not impossible to deal with 
: but should be avoided when possible.

That's the Netgear definition of a Double NAT, which is better
to think of as a NAT-behind-a-NAT.

	client A (e.g. Mac) <-> NAT B (e.g. Airport) <-> NAT C (e.g. modem) <-> Internet

In the real world, a Double NAT refers to the network required
to link two clients behind different NAT boxes connected to
each other.

	client A <-> NAT B <-> Internet <-> NAT C <-> client D

The real world Double NAT is classified by Netgear as a network
with a NAT and a Reverse NAT.


-- 
Eugene
http://www.coxar.pwp.blueyonder.co.uk/