On Friday, April 5, 2002, at 08:42 AM, James_Renkel(_at_)3com(_dot_)com wrote:
[I wrote:]
Also, I think it would be helpful to know how commonly twice-NAT is
deployed, but I don't have any data there.
I believe (at least) twice-NAT is fairly common. I have a NATting router
between by cable access modem and my home's local area network, and my
cable access provider has a NATting router between the cable access
network and the public internet. [...]
I should clarify that I was using the term "twice-NAT" as defined in
section 4.3 of RFC 2663 "NAT Terminology and Considerations" which
actually describes quite a different thing altogether.
Begin excerpt:
Twice NAT is a variation of NAT in that both the source and
destination addresses are modified by NAT as a datagram crosses
address realms. This is in contrast to Traditional-NAT and Bi-
Directional NAT, where only one of the addresses (either source or
destination) is translated. [...]
Your scenario (which is in the same category as my scenario and the
scenario in Appendic C) is not named anywhere I can find. If it has no
name yet, I would propose "compound NAT" or something similar.
I think it's important to distinguish that we're not talking about a
type of NAT here, but rather a way of composing a topology of address
realms using multiple instances of potentially different types of NAT.
(Ick-- I feel dirty just writing that phrase.)
--
j h woodyatt <jhw(_at_)wetware(_dot_)com>