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Pihole with Standard Install
Expected Behaviour:
Running Pi-hole on RPi-4b booting off USB (not micro-SD card). The expected behaviour is for pi-hole to work after restarting the system but whenever my rpi restarts I have to run the "pihole restartdns" command or I can't access the internet. Local connections still work (as expected).
Actual Behaviour:
DNS server is not properly re-routing traffic on fresh boot. Required to restart the dns for the server to work properly.
It sounds a bit like your interface is not ready when Pi-hole has started. You could try to postpone the start by 5 seconds to give the interface some more time.
Add DELAY_STARTUP=5 to /etc/pihole/pihole-FTL.conf and restart Pi-hole.