[plug] failing adsl connection

[Craig Ringer]

> Dont worry about the MTU and MRU values, they are not your problem. The 
> problem is occuring due to inactivity. There is a line you can add to 
> your pppoe config that keeps the connection alive and will automatically 
> attempt to bring it up if it ever goes down, although I can't remember 
> it off the top of my head.

They are your problem if you have a LAN behind your machine that it's 
routing traffic to. PPPoE requires a lower MTU than the maximum for 
Ethernet, and this needs to be configured on the router (by way of 
chopping up packets) or the clients (send smaller packets to start with).

If your DSL modem has a PPPoE client in it, it'll most likely be doing 
this job it's self. If not, the router/gateway host doesn't need to 
worry when it comes to it's own net connection, since it knows the 
desired MTU. However, if you have clients connected to the 
router/gateway that makes the initial PPPoE connection, you'll need to 
be ensuring that packets get fragmented properly or setting a lower MTU 
on the clients. RP-PPPoE's config will handle the fragmentation stuff 
for you, so you generally don't have to worry. Not unless you encounter 
(say) an FTP server that DROPS PACKET FRAGMENTS (yes I've seen this) - 
which is pretty rare and falls in the category of 'what are you ON?!!'

So while the MTU and MRU values are important, under the majority of 
cirvumstances you either don't need to do anything about them, or just 
set one thing in your PPPoE client config to make everything happy.

Craig Ringer