After connecting to my new ISP (Deutsche Glasfaser) successfully via IPv4 (systemd-networkd got a CGNATt’ed address like expected), I noticed that I had no IPv6 address. I then spent days on researching PPPoE, 6rd and what parameters/prefixes/relays my ISP may use, as neither systemd-networkd, NetworkManager nor dhcpcd were even able to find a DHCPv6 server, neither in unconfigured nor configured (routable IPv4) state. Scanning with nmap (sudo nmap (-6) --script broadcast-dhcp(6)-discover) didn’t find anything either.

However, dhclient did, without a hitch.

(0) 30p87@30p87-dns-db:[/etc/systemd/network]$ sudo dhcpcd -6 enp2s0
dhcpcd-10.3.1 starting
DUID 00:01:00:01:31:63:a3:c6:00:10:18:35:c3:1e
enp2s0: IAID 18:35:c3:1e
enp2s0: soliciting an IPv6 router
enp2s0: Router Advertisement from fe80::23
Dropped protocol specifier '.ra' from 'enp2s0.ra'. Using 'enp2s0' (ifindex=2).
enp2s0: soliciting a DHCPv6 lease
timed out
(0) 30p87@30p87-dns-db:[~]$ sudo dhclient -6 enp2s0 -v
Internet Systems Consortium DHCP Client 4.4.3-P1
Copyright 2004-2022 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on Socket/enp2s0
Sending on   Socket/enp2s0
PRC: Confirming active lease (INIT-REBOOT).
XMT: Forming Confirm, 0 ms elapsed.
XMT:  X-- IA_NA 18:35:c3:1e
XMT:  | X-- Confirm Address 2a00:6020:5340::29b4
XMT:  V IA_NA appended.
XMT: Confirm on enp2s0, interval 910ms.
RCV: Reply message on enp2s0 from fe80::23.
RCV:  X-- Server ID: 00:03:00:01:18:c3:00:c3:88:24
message status code Success: "All addresses still on link"
PRC: Bound to lease 00:03:00:01:18:c3:00:c3:88:24.

What really wonders me is that there are no indications from any DHCP client that they even got a response for requesting a v6 address. So it’s not a problem with expecting an address but getting a prefix instead, ig? Configuring that (as seen in https://github.com/systemd/systemd/issues/31820) also doesn’t change anything.

So, ig, either everything but dhclient is borked, or it just automates stuff I don’t know about.

I’d guess I’ll try to capture all packets with wireshark now, and compare eg. systemd-networkd with dhclient.

P.S.: It’s very ironic that a networking community lives on an instance named “itjust.works”