bionic verification:
root@lp1859862-b:~# dpkg -l systemd|grep ii
ii systemd 237-3ubuntu10.39 amd64 system and service manager
root@lp1859862-b:~# cat /proc/sys/net/ipv6/conf/ens3/disable_ipv6
1
root@lp1859862-b:~# ip -6 a show dev ens3
root@lp1859862-b:~# systemctl restart systemd-networkd
root@lp1859862-b:~# ip -6 a show dev ens3
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
inet6 2001:db8::100/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:fe0c:977/64 scope link
valid_lft forever preferred_lft forever
root@lp1859862-b:~# cat /proc/sys/net/ipv6/conf/ens3/disable_ipv6
0
** Tags removed: verification-needed verification-needed-bionic
** Tags added: verification-done verification-done-bionic
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https://bugs.launchpad.net/bugs/1859862
Title:
networkd doesn't re-enable ipv6 unless mtu is set
Status in systemd package in Ubuntu:
Fix Released
Status in systemd source package in Bionic:
Fix Committed
Status in systemd source package in Disco:
Won't Fix
Status in systemd source package in Eoan:
In Progress
Bug description:
[impact]
if the 'disable_ipv6' procfs setting is disabled, and networkd is
configured with ipv6 networking, networkd will not enable ipv6 via the
procfs setting unless the interface mtu is also set to a custom value,
that doesn't match the current interface mtu.
[test case]
create networkd config similar to:
[Match]
MACAddress=52:54:00:0c:09:77
Name=ens3
[Network]
DHCP=ipv4
LinkLocalAddressing=ipv6
Address=2001:db8::100/64
manually disable ipv6 for the interface:
ubuntu@lp1859862-b:~$ echo 1 | sudo tee
/proc/sys/net/ipv6/conf/ens3/disable_ipv6
1
the interface should not contain any ipv6 addresses:
ubuntu@lp1859862-b:~$ ip -6 a show ens3
ubuntu@lp1859862-b:~$
restart networkd; it should enable ipv6 as ipv6 addresses are
configured, but it does not:
ubuntu@lp1859862-b:~$ sudo systemctl restart systemd-networkd
ubuntu@lp1859862-b:~$ ip -6 a show ens3
ubuntu@lp1859862-b:~$
Note that with the mtu set, it will successfully re-enable ipv6;
modify the networkd config to set the mtu by adding this:
[Link]
MTUBytes=1400
(be sure to set the MTU config to something other than its current
mtu)
verify ipv6 is still disabled and has no addresses, then restart and
check again:
ubuntu@lp1859862-b:~$ cat /proc/sys/net/ipv6/conf/ens3/disable_ipv6
1
ubuntu@lp1859862-b:~$ ip -6 a show ens3
ubuntu@lp1859862-b:~$ sudo systemctl restart systemd-networkd
ubuntu@lp1859862-b:~$ cat /proc/sys/net/ipv6/conf/ens3/disable_ipv6
0
ubuntu@lp1859862-b:~$ ip -6 a show ens3
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1400 state UP qlen 1000
inet6 2001:db8::100/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::5054:ff:fe0c:977/64 scope link
valid_lft forever preferred_lft forever
That should be the behavior even if MTUBytes is not set.
[regression potential]
as this adjusts when the procfs 'disable_ipv6' setting is changed, the
regression potential could cause failure to properly set/create ipv6
addresses, or to leave ipv6 disabled entirely.
[scope]
This is needed in Bionic and Eoan.
the commit to fix this is 482efedc081b0c4bf2e77a3dee6b979d9c9a5765
which is included starting in v243, so it is included already in
Focal.
Ignoring Disco, as it is EOL next week.
This problem was introduced by commit
44b598a1c9d11c23420a5ef45ff11bcb0ed195eb, which was included starting
in v239, but also backported to Bionic in bug 1850704.
[other info]
for Eoan, this bug has always existed since release, but for Bionic,
this is a regression introduced by bug 1850704. However, manual
disabling of ipv6 is very unusual, so this bug is unlikely to have an
impact to many systems.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1859862/+subscriptions
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