I have an ethernet connection to my router. I'm running testing version of Debian (though the problem persisted with the stable too) and I don't have any network manager. My /etc/network/interfaces is thusly configured:
# The loopback network interface
auto lo iface lo inet loopback
# The primary network interface
iface eth0 inet static
Every once in awhile the connection just fails; the only pinging that works is to localhost. I've tried using DHCP, which receives offers and generally works well. A temporary fix is to physically unplug the ethernet cable from my computer, wait a few seconds, then plug it back in, a few seconds after doing which the connection works fine again.