Svchost and system connections

I keep getting a firewall pop up telling me another computer wants to connect to me. Sometimes it is “c:\system32\svchost.exe” or a just “system”. I have blocked them as I do not know where they are from.
I have noticed somewhere in this forum that svchost is safe to allow but what about the system attempts.
Can you please advise what to allow or block.
Regards.