Comment 11 for bug 1724895

Matching by MAC address corrects the MTU issue on both Ubuntu 17.10 and Ubuntu 18.04.

I noticed one side effect though - this happened on fresh Ubuntu 17.10 and Ubuntu 18.04 installs. After adding the "match: ... macaddress: ..." parts to the YAML file, running "netplan apply" caused the "ens7" device to be renamed to "eth0". I'm not sure if this is related to my VM configuration, or if it's a bug in netplan. After rebooting, the "ens7" device name was used and the MTU was set properly. Details follow.

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My "/etc/netplan/10-ens7.yaml" contains:

 network:
   version: 2
   renderer: networkd
   ethernets:
  ens7:
    match:
   macaddress: 5a:00:01:7d:18:9a
    mtu: 1450
    dhcp4: no
    addresses: [10.1.96.4/20]

Before running "netplan apply":

 3: ens7: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000
  link/ether 5a:00:01:7d:18:9a brd ff:ff:ff:ff:ff:ff

 ...

After running "netplan apply":

 4: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc fq_codel state UP group default qlen 1000
  link/ether 5a:00:01:7d:18:9a brd ff:ff:ff:ff:ff:ff
  inet 10.1.96.4/20 brd 10.1.111.255 scope global eth0
     valid_lft forever preferred_lft forever
  inet6 fe80::5800:1ff:fe7d:189a/64 scope link
     valid_lft forever preferred_lft forever

Dmesg shows:

 [ 585.985711] IPv6: ADDRCONF(NETDEV_UP): eth0: link is not ready
 [ 586.812306] IPv6: ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready

Journalctl shows:

 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: ens3: Gained IPv6LL
 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: Enumeration completed
 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: ens3: Link is not managed by us
 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: lo: Link is not managed by us
 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: eth0: IPv6 successfully enabled
 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: lo: Link is not managed by us
 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: ens3: DHCPv4 address 45.77.216.215/23 via 45.77.216.1 unit='dbus-org.freedesktop.hostname1.service' requested by ':1.9' (uid=100 pid=925 comm="/lib/systemd/systemd-networkd " label="unconfined")
 May 09 23:03:44 ubuntu1804 systemd-networkd[925]: ens3: Configured
 May 09 23:03:45 ubuntu1804 systemd-networkd[925]: eth0: Gained carrier
 May 09 23:03:47 ubuntu1804 systemd-networkd[925]: eth0: Gained IPv6LL
 May 09 23:03:47 ubuntu1804 systemd-networkd[925]: eth0: Configured