Re: Cisco PIX VPN Pass-Through

[Nick Chettle <lists () mogmail net>]

Hi Jason,

Thanks for the advice.

In order to enable NAT traversal I have to enable isakmp on the internal 
interface. When I do that, it tries to terminate the VPN on the PIX 
itself rather than passing the isakmp packets through to the internet. 
Is there anyway to tell it not to do that?

Thanks, Nick

Hi Nick,

It doesn't look like you have the "isakmp nat-traversal" command
enabled.  Hope this helps, from Cisco documentation:

isakmp nat-traversal

Network Address Translation (NAT), including Port Address
Translation (PAT), is used in many networks where IPSec is also
used, but there are a number of incompatibilities that prevent
IPSec packets from successfully traversing NAT devices. NAT
traversal enables ESP packets to pass through one or more NAT
devices.

The firewall supports NAT traversal as described by Version 2 and
Version 3 of the IETF "UDP Encapsulation of IPsec Packets" draft,
available at http://www.ietf.org/html.charters/ipsec-charter.html,
and NAT traversal is supported for both dynamic and static crypto
maps. NAT traversal is disabled by default on the firewall.

To enable NAT traversal, check that ISAKMP is enabled (you can
enable it with the isakmp enable if_name command) and then use the
isakmp nat-traversal [natkeepalive] command. (This command appears
in the configuration if both ISAKMP is enabled and NAT traversal
is enabled.) If you have enabled NAT traversal, you can disable it
with the no isakmp nat-traversal command. Valid values for
natkeepalive are from 10 to 3600 seconds. The default is 20
seconds.

Jason
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