Is this a particularly sensitive process?
I wouldn't have thought so.
So long as the switch can cope with the L2 broadcast required for PADI, to flood the packet to all ports in the VLAN.
If I have my equipment powered down for an extended period of time the router will not connect to the isp, timeout waiting for PADO packets.
An extended period of time being how long? My initial thought would be how behaviour changes when entries timeout in any ARP caches, or in the MAC table in the switch.
If I switch the router off for only a minute and back on again it will connect again absolutely fine (presumably as the ppp session is still alive)
Surely the PPP session won't still be alive if the router has been power cycled. The router must surely go through the whole PPPoE discovery process again, before then starting a new PPP session.
In the end, it looks as though the modem will talk via a switch only if it has recently talked directly to a router. It is almost as though it is "conditioned" to only be able to deal with one partner MAC address... and only communicates with the same MAC as the first talker.
That makes me wonder if, after the router has been turned off for "an extended period of time". the modem learns to talk to the MAC of the switch (eg if the switch talks VTP, DTP, CDP, LLDP or STP) and refuses to talk to any other piece of equipment (ie the modem).
However, when the modem is directly connected, it learns that the "primary partner MAC" is the router. A short power-cycle isn't enough to dislodge "primary partner" status, so the modem then ignores any frames sent by the switch (VTP, DTP etc) but allows fresh PADIs from the router.
In which case... are there some L2 protocols that you need to turn off?
When my router wont connect I find that if I move it and connect it directly to my modem it will connect again (most of the time) I can then switch the router off and put it back into its original location which is a bit of a pain. I ran a wire shark and I do see the padi request hitting the modem, it just doesn't get a response from the ISP.
How exactly do you see that the PADI hits the modem?
When testing at one point last night I could not get the router to re-connect even when directly connected but for some reason trying a different modem cleared it and it connected, I then reverted immediately to my original setup and all was ok.
Makes me wonder just what kind of MAC caching is going on.
I had that working without using a vlan, just plugging in the modem and router into my LAN at different switches.
Dray has a point here. How do the router & modem behave if there is no VLAN, and they are connected into a single plain switch? Or network of switches?