> Is better in-kernel PPPoE or rp-pppoe ??

This depends. If you have a fast machine, it doesn't matter. If you have
a slow router and/or a fast connection, the in-kernel version will be more
friendly to your CPU cycles.

What is fast enough is not realy clear. If you use that machine only for 
routing and have - say - a 768kbit/s download connection, a Pentium with
100 MHz should be enough to be happy with a userland implementation.

I'm running the in-kernel PPPoE on a SparcStation II with a 128kbit/768kbit
DSL line. The CPU load does not exceed roughly 10% (including NAT).

> does hte in-kernel one works fine ?

For me, yes ;-)

One caveat though: with rp-pppoe you have an option to clamp the advertized
MSS of connections from behind your router. This option, while eating still
more CPU cycles, will allow connections to servers behind broken firewalls.
PPPoE is prone to this problem because of the lower MTU.

There is (currently) no equivalent for the in-kernel implementation.

I hope this will change (and become part of the ipfilter/ipnat code).

Martin