I have similar setup (PPPoE, /48 delegation) here are my network files: (It's been a while, I don't remember the reason for everything)
==> /etc/systemd/network/10-extern0.link <== [Match] Path=platform-fe300000.ethernet [Link] Name=extern0 ==> /etc/systemd/network/10-extern0.network <== [Match] Name=extern0 [Link] RequiredForOnline=degraded ==> /etc/systemd/network/10-intern0.link <== [Match] Path=platform-f8000000.pcie-pci-0000:01:00.0 [Link] Name=intern0 ==> /etc/systemd/network/10-router.network <== [Match] Name=intern0 [Network] Address=192.168.72.1/24 DHCPServer=true IPMasquerade=ipv4 IPv6AcceptRA=no IPv6SendRA=yes DHCPPrefixDelegation=yes MulticastDNS=resolve [DHCPServer] PoolOffset=100 PoolSize=100 EmitDNS=yes DNS=_server_address [IPv6SendRA] DNS=fd07::c09b:1fff:fe46:836e [IPv6Prefix] Prefix=fd07::/64 Assign=true [Link] RequiredForOnline=no ==> /etc/systemd/network/ppp.network <== [Match] Kind=ppp [Network] DHCP=yes KeepConfiguration=yes # I think this was because systemd was messing with the IPv4 config set up by ppp IPv4Forwarding=yes IPv6Forwarding=yes IPv6AcceptRA=yes -- Max Gautier
