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Stephen More wrote:

|
| On 11/14/04, *Charles Steinkuehler* <[EMAIL PROTECTED]
| <mailto:[EMAIL PROTECTED]>> wrote:
| - If you're trying to use the Linksys IPSec 'passthrough' mode, you would
| *NOT* use nat_traversal (ie: they're two different solutions to the same
| problem).  Specifically, try with nat_traversal=no on the LEAF side, and
| the IPSec Passthrough on the Linksys enabled.
|
| Can you provide a good resource on how to debug/troubleshoot ipsec
| connection problems ?

Debuggin IPSec is just a more complex version of standard network
troubleshooting.  Start by understanding the protocols involved, and use
appropriate tools to detect problems.  Typically, packet sniffers and visual
inspection of runtime configurations (ie: tcpdump, ipsec look, etc) are some
of the main tools I use when debugging IPSec links.

| I am currently trying to troubleshoot why I can connect to a VPN using
| ipsec, but I can not send any traffic to hosts behind the VPN server.
|
| At this point I am not sure if it is a ipsec problem/firewall
| problem/routing problem/NAT-T/pass through or a mixture of all.

This could be caused by routing issues, firewall issues (make sure you're
allowing protocols 50/51 as well as UDP port 500, which sets up the SA),
configuration issues (it can be tricky to understand how IPSec interacts
with standard routing on linux).

Without more to go on, I can't suggest any possible solutions, other than to
crawl through the output of "ipsec look" (and ipsec barf, if you're feeling
brave), then dig out tcpdump and start sniffing traffic to make sure the
expected packets are actually showing up on both ends.

NOTE:  Some ISPs actively filter IPSec traffic on 'consumer' or
'residential' service, requiring you to upgrade to a 'business' class
service to use a VPN.  In these cases, you can typically use NAT traversal
(which avoids sending the odd-ball protocol 50/51 traffic, and instead
tunnels it through UDP) to get around the problem.

- --
Charles Steinkuehler
[EMAIL PROTECTED]
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