ubuntu@lp1850704-b:~$ cat /etc/systemd/network/10-ens3.network
[Match]
Name=ens3
[Network]
DHCP=ipv4
LinkLocalAddressing=ipv6
[Link]
MTUBytes=6666
ubuntu@lp1850704-b:~$ dpkg -l systemd|grep ii
ii systemd 237-3ubuntu10.33 amd64 system and service manager
ubuntu@lp1850704-b:~$ ip l show ens3
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 6666 qdisc fq_codel state UP
mode DEFAULT group default qlen 1000
link/ether 52:54:00:86:c7:44 brd ff:ff:ff:ff:ff:ff
ubuntu@lp1850704-b:~$ sudo ip l set mtu 1500 dev ens3
ubuntu@lp1850704-b:~$ ip l show ens3
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP
mode DEFAULT group default qlen 1000
link/ether 52:54:00:86:c7:44 brd ff:ff:ff:ff:ff:ff
ubuntu@lp1850704-b:~$ sudo systemctl restart systemd-networkd
ubuntu@lp1850704-b:~$ ip l show ens3
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 6666 qdisc fq_codel state UP
mode DEFAULT group default qlen 1000
link/ether 52:54:00:86:c7:44 brd ff:ff:ff:ff:ff:ff
** Tags removed: verification-needed verification-needed-bionic
** Tags added: verification-done verification-done-bionic
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https://bugs.launchpad.net/bugs/1850704
Title:
networkd doesn't set MTUBytes if interface is already up
Status in systemd:
Fix Released
Status in systemd package in Ubuntu:
Fix Released
Status in systemd source package in Bionic:
Fix Committed
Bug description:
[impact]
if a networkd .network file specifies a [Link] section with
MTUBytes=XXX set, networkd will only apply that mtu if the interface
is down when networkd starts; if the interface is already up, the mtu
won't be applied.
[test case]
on a bionic system, create a .network file like:
[Match]
Name=ens8
[Link]
MTUBytes=6666
then, reboot. The interface should be set correctly with that mtu:
$ ip l show ens8
3: ens8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 6666 qdisc fq_codel state UP
mode DEFAULT group default qlen 1000
link/ether 52:54:00:30:4c:1e brd ff:ff:ff:ff:ff:ff
now, manually change the interface back to 1500 mtu, and restart networkd,
then recheck the mtu:
$ ip l show ens8
3: ens8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 6666 qdisc fq_codel state UP
mode DEFAULT group default qlen 1000
link/ether 52:54:00:30:4c:1e brd ff:ff:ff:ff:ff:ff
$ sudo ip l set mtu 1500 dev ens8
$ ip l show ens8
3: ens8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP
mode DEFAULT group default qlen 1000
link/ether 52:54:00:30:4c:1e brd ff:ff:ff:ff:ff:ff
$ sudo systemctl restart systemd-networkd
$ ip l show ens8
3: ens8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP
mode DEFAULT group default qlen 1000
link/ether 52:54:00:30:4c:1e brd ff:ff:ff:ff:ff:ff
[regression potential]
low, but any regression would likely involve failure to correctly set
the configured mtu.
this is needed only in bionic, it's fixed in disco and later already.
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