Hi
I don't believe that fibertel is using great tecnology, if they are, then the IT people from there are a mess.
I had LOT's of problems with that provider, my main provider actually is ARNET (PPPoE) and THAT's is what I call a decent (still not good enough) provider, almost NO downtime, no problems of any kind, fast speed, the downside is that It has very high latences compared to fibertel, and a non-existent tech support
that's why I use fibertel as my backup ISP.
you also could add to Fibertel, continuous brownout in their DNS services
and also lost connection 8 to 15 times a week , for at least 30 minutes period (typ: 2hs)
I'm not totally sure that the problem is related to the long DHCP lease, because I can see the resolving problem right after a full powercycle (modem included).
Also I'm using a different modem than you, I had SB5100 about 6 months ago and by my request they changed for a webstar DPC2100 (the ugly little black box), and the problem remains.
To force the ISP to change the IP (just in case that a different IP could solve the problem) I edited the MAC of the NIC card, restart the modem and the IP changed instantly.
Still the same effect.
I gonna have to stay with these 2 providers, they combined gives me 100% uptime and almost a decent traffic capability, at least until IPLAN fiber optic get here, and I'll be happily eferafter
c-u
Lightman