> what am I doing wrong? If I type "tcpdump -xXni sip0 -s 0" tcpdump shows
> me the complete packet data of all ethernet packets. If I use pppoe0
> instead of sip0 tcpdump ignores "-xX" and shows PPPoE + TCP/IP headers
> only.

Very interesting - never noticed this before.

Please file a PR (category "bin") against tcpdump.

This is probably caused by the different link layer encapsulation passed
to bpf (pppoe0 does tap full PPPoE frames, not PPP frames, while ppp0 sends
PPP frames with async encapsulation to bpf)

Martin