Hi,
while I tried to search the discussions, I am not sure my friend’s set-up is typical ppoe scenario, so forgive me the new thread 
I have one friend, who lives in Italy, and his ISP installed MT box for him. They don’t provide him with even read-only access to MT box, so his set-up is as follows:
PC (Debian) (ppoe) —> switch —> MT (in bringe mode, no IP address)
Now - he is reporting some 4% of packet loss on his set-up, and ISP told him, that it is caused by MT not liking this kind of setup via the switch, that the problem is ARP related, and that he should connect his Debian box directly to MT box.
Well, I find it being a nonsense, right? But of course - any guru could confirm/deny it is a nonsense or not?
His Debian config is:
ppp0 Link encap:Point-to-Point Protocol
inet addr:88.213.131.148 P-t-P:88.213.133.1 Mask:255.255.255.255
UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1480 Metric:1
RX packets:196054 errors:0 dropped:0 overruns:0 frame:0
TX packets:154264 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:3
RX bytes:184485411 (175.9 MiB) TX bytes:14729472 (14.0 MiB)
I pointed him out to wiki ppoe page/MTU. Do you think, it could be MTU related = he should lower his MTU on his Debian Box, or even ask his ISP to add something like following line into his MT box?
/ ip firewall mangle add chain=forward protocol=tcp tcp-flags=syn action=change-mss new-mss=1448
Thanks for eventual answers,
Best regard,
Petr