After experiencing a recent problem at our site, I've done some experimentation. We are currently running Debian8 ( DIAL ), or ' RAT_C1 ', from 2017. I started with 2 blank 4Gig SD cards, and installed each version. If this system is booted on ' Rat_C1' WITHOUT Ethernet, Asterisk will NOT start, and there is NO URI connection. Plugging in the Ethernet cable starts Asterisk, and a good URI connection is established. After that, the Ethernet can be removed, and Asterisk will continue to run. The current Debian 9 ( ASL ) does not exhibit this property. I will be changing over to ASL ASAP!