[mythtv-users] Ethernet troubles.

Ronald Frazier ron at ronfrazier.net
Mon Apr 27 15:19:54 UTC 2009


> Actually, being vary pedantic, what you describe is not NAT - it is NAPT
> (Network Address and Port Translation). Pure NAT only does 1-1 address
> mapping (leaving all port numbers unchanged) - so you need as many public
> IPs as you have internal devices you want to map for.

We're being really anal about it by now :) but RFC-2663 doesn't really
seem to agree
http://tools.ietf.org/html/rfc2663

Specifically:
"There are two variations to traditional NAT, namely Basic NAT and
NAPT (Network Address Port Translation)"

In other words, what some here are referring to as "true NAT" or "pure
NAT" is really what the RFC refers to as the "Basic NAT" variation of
"NAT". NAPT is just the other variation of it, but still considered
NAT according to the RFC


> IIRC in the IPTables world it's not even called NAT, but Masquerading.

The table that handles address translation for iptables is called
"nat". "MASQUERADE" is merely a target that is applicable to entries
in the "nat" table. Additionally, it's not meant to be used when you
have a static IP on the WAN.


> NAT is yet another of those terms that has a very precise meaning, but is so
> regularly misused that the correct meaning is no longer recognised.

Ironic that you would say that, given that your definition doesn't fit
with RFC-2663.

-- 
Ron


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