It seems like this scenario isn't covered in any faq:

I have a PPPoE server running on eth1, and want to control
outgoing traffic to users connecting through PPPoE.

Internet --- eth0 - eth1 --- users over PPPoE
                     ppp0
                     ppp1
                     ppp..

Each user is assigned a static address (i.e., user1 is always
10.1.1.1). However, the pppx devices are assigned dynamically based on
the order they connect (if user3 connects first, he gets ppp0).

Should I configure shaping rules (based on IP addresses) on eth1, or
do I have to write a script that is watching the PPPoE logs, figure
out which user is which pppx and add rules to each pppx
accordingly? That is, can I shape on IP on eth1 when I am using PPPoE,
or do I have to shape on each virtual ppp device?

--
LarsG