Public bug reported:
[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.
** Affects: systemd
Importance: Unknown
Status: Unknown
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: Fix Released
** Affects: systemd (Ubuntu Bionic)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Also affects: systemd (Ubuntu Bionic)
Importance: Undecided
Status: New
** Changed in: systemd (Ubuntu)
Status: New => Fix Released
** Changed in: systemd (Ubuntu Bionic)
Assignee: (unassigned) => Dan Streetman (ddstreet)
** Changed in: systemd (Ubuntu Bionic)
Importance: Undecided => Medium
** Changed in: systemd (Ubuntu Bionic)
Status: New => In Progress
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https://bugs.launchpad.net/bugs/1850704
Title:
networkd doesn't set MTUBytes if interface is already up
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