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06.06.2007 at 07:06AM PDT, ID: 22616317
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8.2

General question about getting a VPN through NAT

Asked by tayloenic in IPSec Security Protocol, Virtual Private Networking (VPN), Cisco PIX Firewall

Tags: , ,

I recently had trouble getting an IPSEC vpn to work through NAT.  On one end of the vpn, there was a PIX and on the other end was a cisco 2600 router.  The guy that was helping me fixed it by simply not natting any packets that were exchanged between the two offices that had the vpn.  

interface eth 0/1
ip nat inside source list 150 interface Ethernet0/1 overload

access-list 150 deny   ip 192.168.38.0 0.0.0.255 192.168.47.0 0.0.0.255
access-list 150 permit ip 192.168.38.0 0.0.0.255 any

So any traffic that went specifically between 192.168.38.x and 192.168.47.x did not get natted.  That's where the vpn went.  He added a command on the PIX that accomplshed the same thing.

My question:  This seems like and easy and elegant solution to the problem.  Why is there so much discussion about getting vpns through NAT boxes?  Cisco has created some proprietary protocols (IPSEC over UDP and IPSEC over TCP) and there is the open standard called NAT traversal (NAT-T) protocol.  Why doesn't everyone just bypass the NAT like we did?  After all, one of the primary purposes of NAT is security and the traffic going through the vpn is getting plenty of security.

Thanks,
Tnic
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[+][-]06.06.2007 at 08:41AM PDT, ID: 19226028

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About this solution

Zones: IPSec Security Protocol, Virtual Private Networking (VPN), Cisco PIX Firewall
Tags: vpn, nat, getting
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Solution Provided By: rsivanandan
Participating Experts: 2
Solution Grade: A
 
 
[+][-]06.12.2007 at 01:20PM PDT, ID: 19269512

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