Network Capture on Server Core

Rather than installing 3rd party tools that may or may not work with server core this is built into most recent Windows Server operating systems.

netsh trace start persistent=yes capture=yes tracefile=c:\temp\trace.etl
netsh trace stop

The .etl can be examined using Microsoft Network Monitor or Microsoft Message Analyser

https://blogs.msdn.microsoft.com/canberrapfe/2012/03/30/capture-a-network-trace-without-installing-anything-capture-a-network-trace-of-a-reboot/