[Chilli] Why does CoovaChilli keep getting issue with VPN, How to debug/troubleshoot this issue?

[Le Tran Dat]

 Hi list,

I have been working with CoovaChilli for the past 3 months and I am
getting used to it. However, I am always get trouble with VPN
connection.

Last time I used CoovaChilli 1.2.5 and I managed to let the clients
connecting to Hotspot by marking NOTRACK to raw table as the bellow
rules.

ipt -t raw -I POSTROUTING -j NOTRACK -o $DHCPIF
ipt -t raw -I OUTPUT -j NOTRACK -o $DHCPIF

Now I am using CoovaChilli 1.3.0, I found that my development PC and
another testing PC, both are XP, can create an VPN connection without
adding the above rules. However, some other PCs can not do the same,
they are XP too. If I enable CoovaChilli then I can not connect to VPN
server anymore. I tried to mark NOTRACK to the raw table as well.

I know what I am describing here is so vague since I have no idea why
CoovaChilli has this issue. I hope anyone in the list who had managed
to solve this problem might give me some hints to
debug/troubleshooting this issue.

Currently, what I am doing is just keep changing iptables rules until
I can connect to the VPN server. Anyway, I have no idea how to debug
it, which log I should look into or what I should do to trace down the
issue.

Any of your suggestions are valuable to me.

Thanks,
Dat