If you’ve previously installed VyOS for the purpose of linking your networks by IPsec VPN, you may be tempted to let one of them do DHCP for the others. So you enable DHCP relaying on the router at each site, on all of the interfaces involved. Then you see this in the log:

Sep  9 18:38:00 cr2 dhcrelay: Unsupported device type 768 for "vti0"

768 is ARPHRD_TUNNEL, which may not be so obviously wrong as ARPHRD_NONE but still won’t cut it for DHCP. No can do.