Beaglebone Ethernet Unresponsive Upon Idle

I’m running a BBB with 3.14 Jessie. I have a Verizon cell modem plugged into the USB port. Everything works great. I left the device idle for 1 week and then tried to ping it-- no luck, my pings were not returned. Checking the Verizon network, the cell modem WAS connected. The heartbeat lights on the BBB were operating normally. A power cycle fixed the issue. I’ve actually had this happen not just when using a cellular modem but plain-ol-eth0. Long idles (how long, I don’t know) tend to put the BBB to sleep. At least on the eth0 side, if I go into a BBB terminal and do a ping to the server, the eth0 suddenly wakes up and everything is normal… until the next long idle.

Anyone have any clue what is going on? Is this a power management sleep issue? Can I turn all power management off on everything?