How to log user IP traffic per MAC in DB?

[fatzopilot]

Hi Experts,

We are a small club at the university and want to enable internet access for our members using a VPN tunnel to the university net. So far, every user had to request his/her own VPN user account. However, some members are not enrolled there and thus are unable to get an account. So we want to use internet connection sharing using a single VPN tunnel. I managed to install openwrt (linux based router os) on an asus 500gl premium (router), to establish a VPN tunnel using VPNC, and to restrict access via MAC filter. So we have a working VPN endpoint. Additionally, it is required by the net administration to log all IP traffic and to relate it to individual users (via MAC). MAC spoofing is not considered an issue. So my question is:
How to accomplish best IP traffic logging on a per user/MAC basis?
How to store the logs in an external DB (mySQL)? This is required as we do not want to use the router's flash as the continuous delete/write cycles are likely do destroy it after some time. In memory DB is also no option as a power-cycling could be done easily by users acting in a bad faith.
Any ideas/suggestions/hints?

Thanks in advance
fatzopilot

[fatzopilot]

OK, I tried the following howto

oldwiki.openwrt.org/iptablesULOGmysqlHowTo.html

but when I

>insmod ipt_ULOG

I get an:
cannot insert '/lib/modules/2.6.25.17/ipt_ULOG.ko': invalid parameters (17): Invalid argument (all packages are installed, inlcuding ipt_ULOG).

Any ideas how I might proceed?
Thanks
fatzopilot