nixos/networkd: reimplement useDHCP in a sensible way #167327

lheckemann · 2022-04-05T10:51:44Z

Description of changes

cc people I've talked about this with: @fpletz @Ma27 @globin @WilliButz

This seems like a decent default, with the caveat that the wait-for-online service will not succeed. This can be fixed by setting useDHCP on a specific interface, and doing so is still recommended for this reason.

Things done

Ma27

Seems reasonable 👍

I guess we should also revert the changes in nixos-generate-config then, correct?

Also not sure about the state of networkd-docs in NixOS, but if there are any, this should be noted there as well.

lheckemann · 2022-04-25T15:24:54Z

revert the changes in nixos-generate-config

I think it still makes sense to generate config for known interfaces in order to reduce the impact of the wait-online issue.

Ma27 · 2022-04-25T16:28:32Z

I think it still makes sense to generate config for known interfaces in order to reduce the impact of the wait-online issue.

I haven't used scripted networking in quite a while, but doesn't that hang if an interface from networking.interfaces is not available? THis is e.g. an issue if I have plugged in a smartphone for USB tethering, run nixos-generate-config, the tethering-eth iface is part of hardware-configuration.nix. When I plug it off and reboot, it potentially hangs, correct? See for instance #107908.

If we already go down that route, networking.useDHCP = true; in nixos-generate-config is IMHO the more sensible default. If somebody knows their network well-enough they can still apply some customizations.

lheckemann · 2022-04-25T16:47:20Z

The problem with networking.useDHCP = true in the general case is that a device with multiple matching interfaces (e.g. a laptop with WiFi and Ethernet, which is fairly common) will never reach an "online" state if only one of the interfaces is used (which is also fairly common), even though it's perfectly usable and "online" from a user's perspective. I'd say that useDHCP should indeed default to true, but we should also generate per-interface config and comment that.

Ma27 · 2022-04-25T16:49:56Z

I'd say that useDHCP should indeed default to true, but we should also generate per-interface config and comment that.

Would be OK with that. Also, my concerns only apply to the use of scripted networking, how nixos-generate-config should behave with networkd being the default can be discussed when it's time :)

nixos/tests/networking.nix

Ma27 · 2022-04-29T09:56:00Z

I'd like to see this in 22.05 as this is an important step towards networkd adoption.

Ma27

Also, I'd like to see this implemented:

I'd say that useDHCP should indeed default to true, but we should also generate per-interface config and comment that.

@lheckemann do you want to apply the remaining tasks or do you want me to take over? :)

nixos/modules/tasks/network-interfaces-systemd.nix

…DHCP = true;` Previously this wasn't done in the `forEach`-expression for `cfg.interfaces` and thus `networking.useDHCP` didn't have any effect if no further interface was statically configured.

According to `systemd.network(5)` of systemd v249 this is a valid option. Fixes evaluation of the wildcard network definitions.

Currently we're still using scripted networking by default. A problem with scripted networking is that having `useDHCP` on potentially non-existing interfaces (e.g. an ethernet interface for USB tethering) can cause the boot to hang. Closes NixOS#107908

lheckemann · 2022-04-30T08:36:48Z

I think we need to have another look at the test, because in spite of some glaring issues (as you've pointed out), it was passing!?

EDIT: Oh, I see, you fixed that too :D

lheckemann · 2022-04-30T08:41:21Z

nixos/modules/installer/tools/nixos-generate-config.pl

+  # Enables DHCP on each ethernet and wireless interface. In case of scripted networking
+  # (the default) this is the recommended approach. When using systemd-networkd it's
+  # still possible to use this option, but it's recommended to explicitly set it
+  # per-interface using `networking.interfaces.<interface>.useDHCP`.


I'd say that the optimal configuration is to have both when using networkd: explicit useDHCP per interface for the ones that should be configured for network-online.target, because they're the ones usually used for internet access, and global useDHCP for any extra interfaces that are used occasionally. This is what nixos-generate-config should generate IMHO.

vcunat · 2022-05-23T09:45:14Z

FYI, I see:

dhcpcd[38576]: read_config: /etc/dhcpcd.conf: No such file or directory

I think the only relevant option I have is auto-generated:

  networking.useDHCP = lib.mkDefault true;

(in particular, no networkd)

EDIT: I'm also suspicious of some lesser regression in behavior since 21.11 (in this config), but I haven't had time to look deeper so far.

ncfavier · 2022-06-15T15:35:39Z

nixos/modules/tasks/network-interfaces-systemd.nix

+          # We set RequiredForOnline to false, because it's fairly
+          # common for such devices to have multiple interfaces and
+          # only one of them to be connected (e.g. a laptop with
+          # ethernet and WiFi interfaces). Maybe one day networkd will
+          # support "any"-style RequiredForOnline...


It does now! systemd.network.wait-online.anyInterface = true;

#178046

nixos-discourse · 2022-11-08T21:18:29Z

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/plans-for-the-networkd-infrastructure/23086/3

Configuring dhcp on a per-interface basis is problematic if an interface isn't present at boot time. NixOS/nixpkgs#167327

jfly · 2024-01-03T10:47:52Z

with the caveat that the wait-for-online service will not succeed

What service is this referring to? Is it systemd-networkd-wait-online.service?

Make aragorn act more like a dumb ap should (disable dhcp for ipv4 and ipv6). As a nice side effect, this seems to unbreak ipv6 browsing. Also remove legacy commands about `networking.useDHCP` being deprecacted. It no longer is: NixOS/nixpkgs#167327.

github-actions bot added 6.topic: nixos 8.has: module (update) labels Apr 5, 2022

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lheckemann marked this pull request as ready for review April 5, 2022 20:01

Ma27 reviewed Apr 21, 2022

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ncfavier reviewed Apr 27, 2022

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Ma27 added this to the 22.05 milestone Apr 29, 2022

Ma27 requested changes Apr 29, 2022

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lheckemann requested a review from dasJ as a code owner April 29, 2022 21:36

github-actions bot added 8.has: changelog 8.has: documentation labels Apr 29, 2022

ofborg bot added the 2.status: merge conflict label Apr 29, 2022

lheckemann and others added 8 commits April 30, 2022 00:30

nixos/networkd: reimplement useDHCP in a sensible way

d30dbf3

nixos/tests/networking: add test for global useDHCP

ba4a615

nixos/tests/networking: test connectivity from both client & router

161dd27

nixos/network-interfaces-systemd: actually set catchall-iface if `use…

aa849e1

…DHCP = true;` Previously this wasn't done in the `forEach`-expression for `cfg.interfaces` and thus `networking.useDHCP` didn't have any effect if no further interface was statically configured.

nixos/tests/networking/dhcpDefault: actually use networkd for client

b08a068

nixos/networkd: allow RouteMetric for IPv6AcceptRA

9c18662

According to `systemd.network(5)` of systemd v249 this is a valid option. Fixes evaluation of the wildcard network definitions.

nixos/doc: add release-note entry for networking.useDHCP change

cff16bc

Ma27 force-pushed the networkd-usedhcp branch from c9cb825 to 8e42949 Compare April 29, 2022 22:31

ofborg bot added the ofborg-internal-error label Apr 29, 2022

lheckemann commented Apr 30, 2022

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Ma27 removed the 2.status: merge conflict label Apr 30, 2022

nixos/network-interfaces: remove outdated deprecation information

196c877

bjornfor mentioned this pull request Apr 30, 2022

Undeprecate networking.useDHCP #75515

Closed

cole-h removed the ofborg-internal-error label May 3, 2022

nixos/nixos-generate-config: update comment for useDHCP

f4e5bd8

Ma27 merged commit f0bb39d into NixOS:master May 6, 2022

lheckemann deleted the networkd-usedhcp branch May 7, 2022 08:44

ncfavier reviewed Jun 15, 2022

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ivanbrennan added a commit to ivanbrennan/nixbox that referenced this pull request May 16, 2023

networking.useDHCP is no longer deprecated

dd121c1

Configuring dhcp on a per-interface basis is problematic if an interface isn't present at boot time. NixOS/nixpkgs#167327

ivanbrennan added a commit to ivanbrennan/nixbox that referenced this pull request May 18, 2023

networking.useDHCP is no longer deprecated

1b37e6a

Configuring dhcp on a per-interface basis is problematic if an interface isn't present at boot time. NixOS/nixpkgs#167327

fpletz mentioned this pull request Aug 12, 2023

Using Docker on AWS EC2 breaks EC2 metadata route because of DHCP #109389

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nixos/networkd: reimplement useDHCP in a sensible way #167327

nixos/networkd: reimplement useDHCP in a sensible way #167327

lheckemann commented Apr 5, 2022 •

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nixos-discourse commented Nov 8, 2022

jfly commented Jan 3, 2024

nixos/networkd: reimplement useDHCP in a sensible way #167327

nixos/networkd: reimplement useDHCP in a sensible way #167327

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lheckemann commented Apr 5, 2022 • edited

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