ifup enp1s0. ifup: unknown interface enp1s0

D ebian Network Connection Drops After Suspend.

In trying to bring the interface up with "ifup enp1s0", I get

ifup: unknown interface enp1s0.

How is that possible ? It was working before the system suspended ?

Checking /etc/network/interfaces, there's no entry for the network interface.  Guess that explains the error message.

Edit and add interface details in /etc/network/interfaces

# The primary network interface
auto enp1s0
iface enp1s0 inet dhcp

Bring up the interface

ifup enp1s0

Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/enp1s0/6c:4b:90:62:4d:42
Sending on   LPF/enp1s0/6c:4b:90:62:4d:42
Sending on   Socket/fallback
DHCPDISCOVER on enp1s0 to port 67 interval 4
DHCPREQUEST of on enp1s0 to port 67
DHCPACK of from
RTNETLINK answers: File exists
bound to -- renewal in 98737 seconds.

Interface appears to be working !