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.
----
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
--
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https://bugs.launchpad.net/bugs/1724895
Title:
MTU not applied on private ethernet interfaces
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