networkd: disallow useDHCP #69302

globin · 2019-09-23T14:53:35Z

Motivation for this change

This is preparation to switch to networkd by default in 20.03
Also intended for 19.09, does not change anything in the default config.

Things done

Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
Ensured that relevant documentation is up to date
Fits CONTRIBUTING.md.

Notify maintainers

cc @fpletz @flokli @arianvp @disassembler @lheckemann

fpletz · 2019-09-23T19:43:14Z

@volth Thanks for the hint. I would prefer to add a boot.initrd.network.useDHCP or something under boot.initrd.network.udhcpc. for that use case if needed. But are you really running networkd with networking.useDHCP enabled so that this becomes a real issue?

Note that this module already invokes udhcpc for interfaces that have useDHCP explicitly set, which is also the way we plan to move forward.

Also note that initrd-network does neither use our scripted networking nor dhcpcd as we do later in the running system anyway. So for now I see no immediate reason to change the initrd-network to networkd even if we switch to it by default in stage2.

fpletz · 2019-09-23T20:46:49Z

@globin @andir Regarding 2b605e9, with this change we also can remove the 99-main.network hack altogether.

As mentioned elsewhere this functionality is inherently broken without manually poking around some other network units anyway; for example to make stuff like network-online.target work if you have more than one interface on your system (e.g. RequiredForOnline=).

globin · 2019-09-24T07:38:42Z

Added release notes and information to the option docs.

andir · 2019-09-24T07:57:26Z

nixos/modules/tasks/network-interfaces.nix

@@ -903,6 +903,11 @@ in
        Whether to use DHCP to obtain an IP address and other
        configuration for all network interfaces that are not manually
        configured.
+
+        Using this option is highly discouraged and also incompatible with


Might be a bit far fetched but how do we plan to proceed with installer images if we discourage usage of this? Wouldn't it be best practice to ship the installer with an encouraged configuration? We should be a good example to users and not just tell them to not use it.

Currently working on this

Does networking.interfaces."en*".useDHCP = true work? reason I ask is because setting a wildcard for matchConfig is supported for networkd.

I guess then for the installer image we can then set networking.interfaces."en*".useDHCP = true to get an IP address on all wired connections (seems like a sane default), but it won't try to ask for DHCP leases on bridges, veths etc

IMHO we shouldn't solve this in this PR.

@andir I understood your comment as changing nixos-generate-config, from the conversation I've just had with @fpletz he misunderstood this, so I've added a commit to change nixos-generate-config. It adds networking.useDHCP = false; and adds networking.interfaces.<name>.useDHCP = true; for all interfaces is /sys/class/net except for lo. Virtual interfaces should not be present in our install media anyway.

This setting will be removed with the switch to systemd-networkd. The use of per interface config is encouraged instead.

This sets networking.useDHCP to false and for all interfaces found the per-interface useDHCP to true. This replicates the current default behaviour and prepares for the switch to networkd.

flokli · 2019-09-24T10:55:52Z

nixos/tests/networking.nix

@@ -72,6 +72,7 @@ let
  testCases = {
    loopback = {
      name = "Loopback";
+      machine.networking.useDHCP = false;


can't we just strip all lines setting networking.useDHCP = false; in the tests, if we set it for each interface?

We now assert useDHCP to be false in conjunction with networkd, I didn't want to change the whole test suite that for the most part doesn't use networkd.

Fair - I misread and assumed these change networkd-based tests…

I meant to refer to any networkd-based tests hardcoding machine.networking.useDHCP.

lheckemann · 2019-10-07T09:13:28Z

@GrahamcOfBorg test networking ipv6

lheckemann · 2019-10-07T09:36:02Z

Backported: 907bb84 da9e914 1cb925e

This addresses a new assertion to the way NixOS handles networks with networkd [1]. As a result this disables `networking.useDHCP` globally on all my machines. Explicit interface configuration, as requested by [1] will be handled in separate commits due to separate machines, not all of which I have access to right now. [1] NixOS/nixpkgs#69302

Explicitly enable DHCP on interfaces as requested in [1]. [1]: NixOS/nixpkgs#69302

lheckemann · 2019-10-08T13:59:40Z

Looks like I was a bit hasty with merging this — it broke evaluation for the networkd variant of the networking.virtual test.

The usage of DHCP is no longer global since a while[1] and we now have to explicitly enable it for the interfaces in question. This actually is a good thing and makes it far less problematic if we use tunnel interfaces and other more complicated networking configuration. I added the definitions for all machines where I actually know which interfaces are in use and disabled useNetworkd for shakti, because I don't know the interface names for that machine and the machine currently isn't in use anyway, so we can add it later if needed. [1]: NixOS/nixpkgs#69302 Signed-off-by: aszlig <aszlig@nix.build>

arianvp · 2019-10-14T21:33:06Z

@lheckemann does that mean you reverted those changes for 19.09 or are they still in?

globin · 2019-10-15T07:12:02Z

They are included. The test never ran with networkd, I simply added the useNetworkd = networkd and the failing test probably is a valid issue with our networkd config.

lheckemann · 2019-10-15T15:27:42Z

@arianvp I fixed the evaluation but not the test, 4a03ddd

matthewbauer · 2020-12-27T22:32:22Z

I think this makes hotplugging network devices difficult. The interface name is different depending on which port you have. It takes a long time to boot up if it is missing too (1 min 30 sec by default).

Ma27 · 2020-12-27T22:35:50Z

Not sure if I misunderstand you, but can't you use wildcards for that purpose in networkd? With scripted networking, this is still supported IIRC.

lheckemann · 2020-12-27T23:37:46Z

Concretely for the networkd case:

{
    systemd.network.networks."99-en-dhcp" = {
      matchConfig.Name = "en*";
      networkConfig.DHCP = "yes";
    };
}

to get DHCP on all ethernet devices.

matthewbauer · 2020-12-29T02:00:23Z

@lheckemann Thanks! That helps.

Does nixos-generate-config (https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/installer/tools/nixos-generate-config.pl#L570-L586) need to hardcode these interfaces at all then? If one of those interfaces no longer exists, you get stuck waiting for "network-addresses-en*" or "network-addresses-wl*" to finish (or timeout at 1m 30s) as part of network-setup.service. This could happen frequently if you're switching between ethernet and wifi but have a USB adapter.

arianvp · 2020-12-29T08:59:25Z

A wildcard sounds fine to me instead of a fixed interface

lheckemann · 2020-12-29T12:18:20Z

The problem with that approach is that it doesn't work with scripted networking, which is still our default.

matthewbauer · 2020-12-29T21:27:14Z

Opened #107908 to track this.

globin changed the title ~~networkd: disallow dhcp~~ networkd: disallow useDHCP Sep 23, 2019

ofborg bot added 6.topic: nixos 8.has: module (update) labels Sep 23, 2019

globin force-pushed the networkd-disallow-dhcp branch from 6616d2c to bead600 Compare September 23, 2019 15:15

ofborg bot added 10.rebuild-darwin: 0 10.rebuild-linux: 0 labels Sep 23, 2019

Ma27 approved these changes Sep 23, 2019

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fpletz requested a review from andir September 23, 2019 20:47

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globin added 3 commits September 24, 2019 10:20

networking.useDHCP: add release notes and docs

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globin force-pushed the networkd-disallow-dhcp branch from 6aa0e98 to 5ee383e Compare September 24, 2019 09:44

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flokli mentioned this pull request Sep 25, 2019

networkd: don't managed interfaces set up by script #48811

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Merge branch 'master' into networkd-disallow-dhcp

68b42a8

lheckemann merged commit 0b754fb into NixOS:master Oct 7, 2019

lheckemann deleted the networkd-disallow-dhcp branch October 7, 2019 09:29

devhell added a commit to openlab-aux/vuizvui that referenced this pull request Oct 8, 2019

machines/gunnr: Explicitly enable DHCP

e88e4a0

Explicitly enable DHCP on interfaces as requested in [1]. [1]: NixOS/nixpkgs#69302

This was referenced Oct 14, 2019

Various software refuses to bind to it's listenaddress #71106

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DHCP gives ip to bridges #67966

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arcnmx mentioned this pull request Oct 15, 2019

nixos/digital-ocean-image: init (rebase) #66978

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matthewbauer mentioned this pull request Dec 29, 2020

nixos-generate-config produces network configuration that times out when interface is removed #107908

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networkd: disallow useDHCP #69302

networkd: disallow useDHCP #69302

globin commented Sep 23, 2019 •

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networkd: disallow useDHCP #69302

networkd: disallow useDHCP #69302

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globin commented Sep 23, 2019 • edited Loading

Motivation for this change

Things done

Notify maintainers

fpletz commented Sep 23, 2019

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globin commented Sep 24, 2019

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