Public bug reported: 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. ** Affects: systemd (Ubuntu) Importance: Undecided Status: New ** Description changed: 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): - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: New device has no master, continuing without - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Flags change: +UP +LOWER_UP +RUNNING +MULTICAST +BROADCAST - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Link 2 added - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: udev initialized link - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Saved original MTU: 1420 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding address: fe80::4001:aff:fea4:2/64 (valid forever) - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Gained IPv6LL - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding address: 10.164.0.2/32 (valid for 15h 15s) - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding route: dst: ff00::/8, src: n/a, gw: n/a, prefsrc: n/a - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding route: dst: fe80::4001:aff:fea4:2/128, src: n/a, gw: n/a, prefsrc: n/a - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding route: dst: fe80::/64, src: n/a, gw: n/a, prefsrc: n/a - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Link state is up-to-date - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: found matching network '/run/systemd/network/10-netplan-ens4.network' - Apr 23 09:51:00 host systemd-networkd[1737]: Setting '/proc/sys/net/ipv6/conf/ens4/proxy_ndp' to '0' - Apr 23 09:51:00 host systemd-networkd[1737]: Setting '/proc/sys/net/ipv6/conf/ens4/use_tempaddr' to '0' - Apr 23 09:51:00 host systemd-networkd[1737]: Setting '/proc/sys/net/ipv6/conf/ens4/accept_ra' to '0' - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Started LLDP. - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Setting address genmode for link - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Setting address genmode done. - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Removing address 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Acquiring DHCPv4 lease - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Discovering IPv6 routers - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Removing address: 10.164.0.2/32 (valid for 15h 15s) - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Removing route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: DHCPv4 address 10.164.0.2/32 via 10.164.0.1 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Setting MTU: 1460 - Apr 23 09:51:00 host systemd-networkd[1737]: Setting '/proc/sys/net/ipv6/conf/ens4/disable_ipv6' to '0' - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: IPv6 successfully enabled - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Setting MTU done. - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Updating address: 10.164.0.2/32 (valid for 1d) - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Adding route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Configuring route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Configuring route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Updating route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Updating route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 - Apr 23 09:51:00 host systemd-networkd[1737]: ens4: Configured - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: DHCP lease lost - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Removing address 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Setting MTU: 1420 - Apr 23 21:50:59 host systemd-networkd[1737]: Setting '/proc/sys/net/ipv6/conf/ens4/disable_ipv6' to '0' - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: IPv6 successfully enabled - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: DHCPv4 address 10.164.0.2/32 via 10.164.0.1 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Removing route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Removing route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Removing address: 10.164.0.2/32 (valid for 12h 1s) - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Removing route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Setting MTU done. - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Adding address: 10.164.0.2/32 (valid for 1d) - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Adding route: dst: 10.164.0.2/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Configuring route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Configuring route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Updating route: dst: 10.164.0.1/32, src: n/a, gw: n/a, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Updating route: dst: n/a, src: n/a, gw: 10.164.0.1, prefsrc: 10.164.0.2 - Apr 23 21:50:59 host systemd-networkd[1737]: ens4: Configured + 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. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1874661 Title: networkd sometimes doesn't set mtu received by dhcp To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1874661/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
