[Bug 1779721] Re: systemd-networkd does not configure DHCPv4

[Benjamin Drung]

My interpretation of the documentation was that an empty match entry
matches everything. I changed the configuration to enforce the matching
and it still fails:

```
root at ubuntu:~# cat /etc/netplan/01-netcfg.yaml  
# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
  version: 2
  renderer: networkd
  ethernets:
    all:
      match:
        name: ens*
      dhcp4: yes
root at ubuntu:~# networkctl 
IDX LINK             TYPE               OPERATIONAL SETUP     
  1 lo               loopback           carrier     unmanaged 
  2 ens6             ether              degraded    configuring

2 links listed.
root at ubuntu:~# networkctl status ens6
* 2: ens6
       Link File: /lib/systemd/network/99-default.link
    Network File: /run/systemd/network/10-netplan-all.network
            Type: ether
           State: degraded (configuring)
            Path: pci-0000:00:06.0
          Driver: virtio_net
          Vendor: Red Hat, Inc.
           Model: Virtio network device
      HW Address: 02:01:71:8f:cc:72
         Address: fe80::1:71ff:fe8f:cc72
root at ubuntu:~# cat /run/systemd/network/10-netplan-all.network
[Match]
Name=ens*

[Network]
DHCP=ipv4

[DHCP]
UseMTU=true
RouteMetric=100
root at ubuntu:~# journalctl -u systemd-networkd
Jul 03 08:52:33 ubuntu systemd[1]: Starting Network Service...
Jul 03 08:52:33 ubuntu systemd-networkd[447]: Enumeration completed
Jul 03 08:52:33 ubuntu systemd[1]: Started Network Service.
Jul 03 08:52:33 ubuntu systemd-networkd[447]: lo: Link is not managed by us
Jul 03 08:52:33 ubuntu systemd-networkd[447]: ens6: IPv6 successfully enabled
Jul 03 08:52:33 ubuntu systemd-networkd[447]: ens6: Gained carrier
Jul 03 08:52:35 ubuntu systemd-networkd[447]: ens6: Gained IPv6LL
```

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https://bugs.launchpad.net/bugs/1779721

Title:
  systemd-networkd does not configure DHCPv4

Status in netplan.io package in Ubuntu:
  New
Status in systemd package in Ubuntu:
  New

Bug description:
  I have an up-to-date Ubuntu 18.04 (bionic) server installation (with
  systemd 237-3ubuntu10) which has following netplan configuration:

  ```
  root at ubuntu:~# cat /etc/netplan/01-netcfg.yaml 
  # This file describes the network interfaces available on your system
  # For more information, see netplan(5).
  network:
    version: 2
    renderer: networkd
    ethernets:
      all:
        match: {}
        dhcp4: yes
  root at ubuntu:~# cat /run/systemd/network/10-netplan-all.network  
  [Match]

  [Network]
  DHCP=ipv4

  [DHCP]
  UseMTU=true
  RouteMetric=100
  ```

  Despite having DHCPv4 configured, no IPv4 address is configured on the
  ethernet device:

  ```
  root at ubuntu:~# ip a show ens6
  2: ens6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 64000 qdisc fq_codel state UP group default qlen 1000
      link/ether 02:01:71:8f:cc:72 brd ff:ff:ff:ff:ff:ff
      inet6 fe80::1:71ff:fe8f:cc72/64 scope link
         valid_lft forever preferred_lft forever
  ```

  The kernel dmesg has no related messages and the journal log also
  looks normal:

  ```
  root at ubuntu:~# journalctl -u systemd-networkd
  Jul 02 16:36:51 ubuntu systemd[1]: Starting Network Service...
  Jul 02 16:36:51 ubuntu systemd-networkd[1790]: ens6: Gained IPv6LL
  Jul 02 16:36:51 ubuntu systemd-networkd[1790]: Enumeration completed
  Jul 02 16:36:51 ubuntu systemd[1]: Started Network Service.
  Jul 02 16:36:51 ubuntu systemd-networkd[1790]: lo: Link is not managed by us
  Jul 02 16:36:51 ubuntu systemd-networkd[1790]: lo: Configured
  ```

  Calling dhclient sets up the device correctly:

  ```
  root at ubuntu:~# dhclient ens6
  root at ubuntu:~# cat /var/lib/dhcp/dhclient.leases
  lease {
    interface "ens6";
    fixed-address 87.106.172.36;
    option subnet-mask 255.255.255.255;
    option dhcp-lease-time 600;
    option routers 87.106.172.1;
    option dhcp-message-type 5;
    option domain-name-servers 46.16.74.70,46.16.72.37;
    option dhcp-server-identifier 87.106.172.1;
    option interface-mtu 64000;
    option host-name "ubuntu-18_04-fkb-2018-07-02";
    renew 1 2018/07/02 16:46:51;
    rebind 1 2018/07/02 16:51:31;
    expire 1 2018/07/02 16:52:46;
  }
  root at ubuntu:~# ip a show ens6
  2: ens6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 64000 qdisc fq_codel state UP group default qlen 1000
      link/ether 02:01:71:8f:cc:72 brd ff:ff:ff:ff:ff:ff
      inet 87.106.172.36/32 brd 87.106.172.36 scope global ens6
         valid_lft forever preferred_lft forever
      inet6 fe80::1:71ff:fe8f:cc72/64 scope link 
         valid_lft forever preferred_lft forever
  ```

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