"Roeland Meyer" <rmeyer@mhsc.com> wrote:
Absolutely true. I'll take that clarification. Not one of mine, but more or less what I was thinking.
|> which of course *is* possible for at least one machine per visible IP |> address - even if additional IPs are masqed behind it. if you are doing one:one NAT then why do NAT at all? Plenty of reasons - you can have an entire 1918 network behind there, and only one or two machines "visible"; by using NAT rather than directly feeding those IP addresses to the machines involved, you simplify routing and separate admin of internal and external (if you need to fall back to a backup machine, you can have it running live in parallel, and one config change on the NAT will change the visible machine) It is pretty common practice for a company with a small (/24 say) allocation to static-NAT one or more to individual servers inside their lan, particuarly if those servers have functions like web proxy or email server.
if you are doing one:many then it won't work (broken). no, it *will* work for the one that is the default.
working from a one-IP allocation, let us assume a 1918 subnet on 192.168.123.x for the backend lan "web.mycompany.com" 192.168.123.5 "ftp.mycompany.com" 192.168.123.10 "webproxy.mycompany.com" 192.168.123.15 "Teleconferencing.mycompany.com" 192.168.123.20 "natdevice.mycompany.com" 192.168.123.25 Workpc1-->Workpc40 192.168.123.101 -->192.168.123.40 bearing in mind that "natdevice.mycompany.com" is also the external visible IP (via a separate interface) do suitably stateful Nat: for inbound port 80 - rewrite packet to web.mycompany.com for inbound port 25 - rewrite packet to ftp.mycompany.com for outbound from webproxy.mycompany.com or teleconferencing.mycompany.com - do stateful NAT for outbound from any other machine - ignore for inbound not covered by above - rewrite packet to Teleconferencing.mycompany.com with this setup, Teleconferencing.mycompany.com will appear to the internet to be listening on whatever ports it chooses to support, and also appear to be doing a whole heap of other things that it really isn't. In practice, a company would probably want to spread out the IPs here a little and get a bigger allocation, but it *could* be done this way if it had to be.