it looks like your dhcp lease is expiring, which causes networkd to drop your dhcp configuration, including resetting your mtu back to its original value. That's done asynchronously by netlink, and networkd sets a flag "setting_mtu" while the netlink request to change the mtu is pending.
However, immediately after your lease is lost, you regain it, and networkd begins setting up the interface with the dhcp info, including the mtu. Unfortunately, since the mtu reset hasn't completed yet, "setting_mtu" flag is still set, and the call to link_set_mtu() returns silently without actually changing the mtu. At least that's what seems like is happening in your case. It's unusual to lose your dhcp lease before renewing it, so you may be able to look at why that's happening to avoid this (hopefully that's not a separate bug in systemd...), but re: the failure to set mtu, I believe that's going to be a problem that still exists upstream, so resolving this bug will need fixing upstream first. If you (or anyone else) has time to open a bug upstream for this (preferably, after testing with upstream systemd to verify it's still a bug upstream), please add a note to this bug. -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/1874661 Title: networkd sometimes doesn't set mtu received by dhcp Status in systemd package in Ubuntu: Confirmed Bug description: I'm running ubuntu-minimal-1910-eoan on google compute engine with systemd 242-7ubuntu3.7. GCE has mtu 1460, set by dhcp. After having networking issues, I figured out that the mtu on the interface was sometimes incorrectly set to 1500. I manually changed it to 1420 to have a working system again and enabled debugging for systemd-networkd. Log (filtered for ens4, some columns removed for better readability): 09:51:00 ens4: New device has no master, continuing without 09:51:00 ens4: Flags change: +UP +LOWER_UP +RUNNING +MULTICAST +BROADCAST 09:51:00 ens4: Link 2 added 09:51:00 ens4: udev initialized link 09:51:00 ens4: Saved original MTU: 1420 09:51:00 ens4: Adding address: fe80::4001:aff:fea4:2/64 (valid forever) 09:51:00 ens4: Gained IPv6LL 09:51:00 ens4: Adding address: 10.164.0.2/32 (valid for 15h 15s) 09:51:00 ens4: Adding route: dst: ff00::/8, src: n/a, gw: n/a, prefsrc: n/a 09:51:00 ens4: Adding route: dst: fe80::4001:aff:fea4:2/128, src: n/a, gw: n/a, prefsrc: n/a 09:51:00 ens4: Adding route: dst: fe80::/64, src: n/a, gw: n/a, prefsrc: n/a 09:51:00 ens4: Adding route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 09:51:00 ens4: Adding route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 09:51:00 ens4: Adding route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 09:51:00 ens4: Link state is up-to-date 09:51:00 ens4: found matching network '/run/systemd/network/10-netplan-ens4.network' 09:51:00 Setting '/proc/sys/net/ipv6/conf/ens4/proxy_ndp' to '0' 09:51:00 Setting '/proc/sys/net/ipv6/conf/ens4/use_tempaddr' to '0' 09:51:00 Setting '/proc/sys/net/ipv6/conf/ens4/accept_ra' to '0' 09:51:00 ens4: Started LLDP. 09:51:00 ens4: Setting address genmode for link 09:51:00 ens4: Setting address genmode done. 09:51:00 ens4: Removing address 10.164.0.2 09:51:00 ens4: Acquiring DHCPv4 lease 09:51:00 ens4: Discovering IPv6 routers 09:51:00 ens4: Removing address: 10.164.0.2/32 (valid for 15h 15s) 09:51:00 ens4: Removing route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 09:51:00 ens4: DHCPv4 address 10.164.0.2/32 via 10.164.0.1 09:51:00 ens4: Setting MTU: 1460 09:51:00 Setting '/proc/sys/net/ipv6/conf/ens4/disable_ipv6' to '0' 09:51:00 ens4: IPv6 successfully enabled 09:51:00 ens4: Setting MTU done. 09:51:00 ens4: Updating address: 10.164.0.2/32 (valid for 1d) 09:51:00 ens4: Adding route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 09:51:00 ens4: Configuring route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 09:51:00 ens4: Configuring route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 09:51:00 ens4: Updating route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 09:51:00 ens4: Updating route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 09:51:00 ens4: Configured 21:50:59 ens4: DHCP lease lost 21:50:59 ens4: Removing address 10.164.0.2 21:50:59 ens4: Setting MTU: 1420 21:50:59 Setting '/proc/sys/net/ipv6/conf/ens4/disable_ipv6' to '0' 21:50:59 ens4: IPv6 successfully enabled 21:50:59 ens4: DHCPv4 address 10.164.0.2/32 via 10.164.0.1 21:50:59 ens4: Removing route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 21:50:59 ens4: Removing route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 21:50:59 ens4: Removing address: 10.164.0.2/32 (valid for 12h 1s) 21:50:59 ens4: Removing route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 21:50:59 ens4: Setting MTU done. 21:50:59 ens4: Adding address: 10.164.0.2/32 (valid for 1d) 21:50:59 ens4: Adding route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 21:50:59 ens4: Configuring route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 21:50:59 ens4: Configuring route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 21:50:59 ens4: Updating route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 21:50:59 ens4: Updating route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 21:50:59 ens4: Configured On dhcp renew (09:51:00), mtu got properly changed to 1460. On next dhcp renew (21:50:59) it got changed back to previous value 1420. In all cases, /run/systemd/netif/leases/2 correctly contained MTU=1460. There have been some changes to mtu handling in the past, I assume this is a regression, potentially from https://github.com/systemd/systemd/issues/12552 or https://github.com/systemd/systemd/issues/6593. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1874661/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
