It is working now. I've done it with Linksys and Netopia DSL routers. Software client on the laptop that DOES tunnel mode ESP. No AH and running through a PAT and it works flawlessly. I just want to know how it works, I've already determined that it does. The point where my logic fails is where PAT relies on modifying the TCP/UDP port numbers, an ESP packet has a standard IP header with an additional protocol 50 ESP header. Since there is no ports to change to create a table to keep track of which packet came from which internal client, what is used to keep track. Someone said something about the UDP encapsulation, but what about the NETOPIA which doesn't do that? -=Vandy=- -----Original Message----- From: Steven M. Bellovin [mailto:smb@research.att.com] Sent: Thursday, September 13, 2001 5:21 PM To: Vandy Hamidi Cc: nanog@merit.edu Subject: Re: IPSEC and PAT In message <912A91BC69F4D3119D1B009027D0D40C01BB459C@exchange1.secure.insweb.co m>, Vandy Hamidi writes:

I know that in Tunnel Mode, IPsec can be NATed and PATed (without IKE on

UDP

500 being used), but as I'm trying to break down the process of how it is working, I've been stumped by this: NAT - Changes source IP during translation PAT - Changes source IP and TCP/UDP port to another to track multiple to one translations. My question is, how does PAT track the packets with their internal hosts when there is not a TCP/UDP header to translate. How does it know which "internal" host a returning ESP packet must be forwarded to after it un PATs the incoming packet? thanks and I hope this isn't a totally stupid question. If it is, humor me ;),

IPsec can't be PATted, because the TCP and UDP port numbers are in the protected part of the packet. --Steve Bellovin, http://www.research.att.com/~smb http://www.wilyhacker.com