Slightly OT: How common is NAT?

Anthony David adavid at
Mon Dec 16 10:51:46 EST 2002

Alex Satrapa <grail at> writes:

> Anthony David wrote:
> >One Govt Agency got a B class allocated (they have about 400-600 IPs in
> >use). They use it for both LAN and Internet addressing and use Firewalling
> >to manage Internet traffic. Messy.
> >
> And then stated:
> >IMHO, NAT is something you do as a last resort. Trouble-shooting
> >is especially exciting when one side refers to an IP and the other side
> >has a different number.
> >
> So if one option is to use real IPs, and that's messy, and the last
> resort is to use NAT (which guarantees that your private network
> addresses are unroutable, and therefore to some extent "secure" from
> messups), what's inbetween?

Don't let your users connect directly to the Internet. There is
no real need unless they want to use chat clients etc. I have
never seen a credible business case for them. All the users' Internet
needs are met by using applicaton proxies and mail servers.

> Protocols that tell the other end what the IP is supposed to be are -
> in my mind at least - somewhat broken. The other end should be able to
> detect the source IP address, since that's included as part of the
> protocol. If you're trying to prevent man-in-the-middle attacks, use
> IPSec to certify that the connection came from someone you trust.
> NAT is a great way to give your tens, hundreds or thousands of desktop
> machines access to the Internet without having to allocate each of
> them a real IP address. Using NAT and private addresses means that
> your Windows machines are no longer vulnerable to network level
> attacks from outside your network.

Anthony David

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