Re: VPN connection question.

  • From: "Thor" <thor@xxxxxxxxxxxxxxx>
  • To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
  • Date: Thu, 9 Sep 2004 13:57:52 -0700

Not just NAT-T... L2TP requires ISAKMP for setup as well. NAT-T, once negotiated, floats to 4500. Oh, and just to follow up on the original "NAT-T 4500" conversation, I ran a 3 *day* packet trace running both 1:1 NAT-T L2TP connections, as well as running 8 simultaneous NAT-T VPN's (L2TP behind NAT) all sourced behind the same NAT device to the same ISA VPN server (N:1) and every single NAT-T packet, from every single session (again all simultaneous connections) were source and destination udp 4500. Every single one.

So, while the RFC's are still in draft state, and while there does seem to be some language about how the NAT-T response must reply on the same port as initiated (after jumping to 4500) that support for non-4500 initiated NAT-T tunnels might exist (presumably for older NAT equipment) the "source 4500/destination 4500" rule seems proper. In the well-over-a-year timeframe that I have had both our border router ACL'd as such as well as the ISA VPN server rules as such, I have never had to change a thing to allow NAT-T connections- every packet from every NAT-T connection has always been 4500<->4500.

This is further supported by the Win2003 "Configuring Firewalls" technet document stipulating one limit source and destination for NAT-T to 4500.

Just to follow up.

T



----- Original Message ----- From: "Jim Harrison" <jim@xxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Thursday, September 09, 2004 12:11 PM
Subject: [isalist] Re: VPN connection question.



http://www.ISAserver.org

Use PPTP.
"Port 500" is only useful for IPSec NAT-T

 Jim Harrison
 MCP(NT4, W2K), A+, Network+, PCG
 http://isaserver.org/Jim_Harrison/
 http://isatools.org
 Read the help / books / articles!

----- Original Message ----- From: "John Tolmachoff (Lists)" <johnlist@xxxxxxxxxxxxxxxxxxx>
To: "[ISAserver.org Discussion List]" <isalist@xxxxxxxxxxxxx>
Sent: Thursday, September 09, 2004 12:08
Subject: [isalist] VPN connection question.



http://www.ISAserver.org

What is the possible way for a remote client to connect to ISA 2000 on
Windows 2003 server to access the local domain/network if the remote client
is on a cable connection where port 500 is blocked?


John Tolmachoff
Engineer/Consultant/Owner
eServices For You




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