I'm **not** an expert on this, so more qualified
people may want to correct what I say below. The
general concepts should be okay and will hopefully
help Tim out.
Tim,
1. IPSec has two modes--tunnel and transport. Tunnel
mode might work for you.
Per
http://www.microsoft.com/technet/security/topics/networksecurity/ipsecarc.mspx#EYF:
"The tunnel mode is used in cases when security is
provided by a device that did not originate packets -
as in the case of VPNs - or when the packet needs to
be secured to a destination that is different from the
actual destination."
As I understand it, IPSec has two parts--AH (header
related) and ESP (data payload related).
Theoretically, if IPSec can be set to only encrypt the
payload of each data packet and not encrypt a packet's
headers, it should work with NAT. I'm not sure how
much this would decrease IPSec's security.
After a quick look, I found a note on the Internet
that implies that something like this may work. Per
http://marc2.theaimsgroup.com/?l=vpn&m=102796863626037&w=2:
"I understand that using AH in tunnel mode is
imcompatible with NAT as NAT rewrites the IP header
and thus breaks the AH header. Is this the only IPSec
mode that is incompatible with NAT? e.g., AH +
Transport, ESP + Tunnel or Transport work with NAT,
correct?"
In response
(http://marc2.theaimsgroup.com/?l=vpn&m=102796980027381&w=2),
someone says:
"AH in any mode is incompatible with NAT or PAT
(NAPT).
ESP in transport mode is incompatible with NAT of PAT
(NAPT), if you are using UDP or TCP, since the TCP or
UDP checksum will break. In other words, it's
incompatible for anything useful.
ESP in tunnel mode itself is not completely compatible
with NAT or PAT (NAPT), depends on how smart your PAT
(NAPT) box is (most are stupid)."
or
2. Another encryption method may suffice...maybe a
type of S/Mime implementation?
or
3. Can you offload the IPSec encryption/decryption to
hardware (such as an "IPSec hardware accelerator") or
a server in front of the NAT device? If so, you may be
able to do something like this:
IPSec traffic <-IPSec-> IPSec decryption device
(immediately in front of the NAT router) <-TCP/IP->
NAT router <-TCP/IP-> Exchange server
Good luck.
Scott
--- timpacalypse@yahoo.com wrote:
I'm curious about how people are implementing FE/BE
Exchange communication.
[...]
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