[Bug 1759014] Re: Netplan has no way to control DHCP client

[Mathieu Trudel-Lapierre]

** Description changed:

- Currently DHCP appears to be an all or nothing boolean, which is
- insufficient for many network configurations.
+ [Impact]
+ DHCP configurations where custom settings (routes, nameservers, etc.) need to be applied.
+ 
+ [Test case]
+ 1) Configure netplan for the particulars of the network by configuring an appropriate dhcp{4,6}-override stanza:
+ 
+ network:
+   version: 2
+   ethernets:
+     engreen:
+       dhcp4: true
+       dhcp4-overrides:
+         use-dns: false
+         use-routes: false
+         route-metric: 3333
+ 
+ Additionally, if so required, add a custom DNS / routes to the
+ configuration. e.g.
+ 
+       nameservers:
+         search: [lab, kitchen]
+         addresses: [8.8.8.8]
+ 
+ (See https://netplan.io/reference#dhcp-overrides for the available
+ options)
+ 
+ 2) Run 'netplan apply' or reboot to have the configuration applied.
+ 3) Validate that the routes / DNS are properly ignored and/or replaced by the defined values.
+ 
+ [Regression potential]
+ Minimal; this adds new values to the configuration generated for networkd or NetworkManager. Existing configurations will remain unchanged, but new configurations using the dhcp{4,6}-overrides fields will benefit from additional flexibility.
+ 
+ 
+ ---
+ 
+ 
+ Currently DHCP appears to be an all or nothing boolean, which is insufficient for many network configurations.
  
  Ideally all of the DHCP configuration options supported by systemd would also be supported in netplan:
  https://www.freedesktop.org/software/systemd/man/systemd.network.html#%5BDHCP%5D%20Section%20Options
  
- 
  As an example, consider the following netplan configuration:
  
  network:
-   version: 2
-   renderer: networkd
-   ethernets:
-     enp0s3:
-       dhcp4: yes
-       nameservers: [8.8.8.8,8.8.4.4]
+   version: 2
+   renderer: networkd
+   ethernets:
+     enp0s3:
+       dhcp4: yes
+       nameservers: [8.8.8.8,8.8.4.4]
  
- 
- After running netplan apply I check the nameservers with systemd-resolve --status and it shows:
+ After running netplan apply I check the nameservers with systemd-resolve
+ --status and it shows:
  
  DNS Servers: 8.8.8.8
-              8.8.4.4
-              192.168.1.1
+              8.8.4.4
+              192.168.1.1
  
  Here, "192.168.1.1" was provided by my DHCP server.  On this particular
  node, I only want the manually configured DNS servers, but netplan has
  no way to indicate this.

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https://bugs.launchpad.net/bugs/1759014

Title:
  Netplan has no way to control DHCP client

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