In my testing on Xenial, you cannot set a child interface MTU to a value greater than its parent. For example, if eth0's MTU is 1500, setting eth0.100's MTU to 9000 (or 1501) causes:
SIOCSIFMTU: Numerical result out of range This restriction makes sense when you consider the physical topology, since packets from eth0.100 would be sent via eth0. If the system attempts to send a packet larger than 1500 bytes via eth0 in this case, it would be dropped. This issue makes me wish it were possible to set a "L3 MTU" (i.e., one that would be the default PMTU MSS, and fragment threshold for other packet types such as UDP and ICMP). -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to ifupdown in Ubuntu. https://bugs.launchpad.net/bugs/1565804 Title: ifup of vlan interfaces failing during networking start - RTNETLINK answers: File exists Status in ifupdown package in Ubuntu: New Bug description: /e/n/i: auto lo iface lo inet loopback dns-nameservers 10.245.168.2 dns-search dellstack auto eth0 iface eth0 inet static gateway 10.245.168.1 address 10.245.168.17/21 dns-nameservers 10.245.168.2 mtu 1500 auto eth1 iface eth1 inet manual mtu 1500 auto eth1.2667 iface eth1.2667 inet static address 10.245.184.20/24 vlan-raw-device eth1 mtu 9000 vlan_id 2667 output from networking startup: ● networking.service - Raise network interfaces Loaded: loaded (/lib/systemd/system/networking.service; enabled; vendor preset: enabled) Drop-In: /run/systemd/generator/networking.service.d └─50-insserv.conf-$network.conf Active: failed (Result: exit-code) since Mon 2016-04-04 12:14:26 UTC; 1h 33min ago Docs: man:interfaces(5) Process: 1255 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=1/FAILURE) Process: 868 ExecStartPre=/bin/sh -c [ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifquery --read-environment --list --exclude=lo)" ] && udevadm settle (code=exited, Main PID: 1255 (code=exited, status=1/FAILURE) Apr 04 12:14:25 reflecting-attraction systemd[1]: Starting Raise network interfaces... Apr 04 12:14:26 reflecting-attraction ifup[1255]: Set name-type for VLAN subsystem. Should be visible in /proc/net/vlan/config Apr 04 12:14:26 reflecting-attraction ifup[1255]: RTNETLINK answers: File exists Apr 04 12:14:26 reflecting-attraction ifup[1255]: Failed to bring up eth1.2667. Apr 04 12:14:26 reflecting-attraction systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE Apr 04 12:14:26 reflecting-attraction systemd[1]: Failed to start Raise network interfaces. Apr 04 12:14:26 reflecting-attraction systemd[1]: networking.service: Unit entered failed state. Apr 04 12:14:26 reflecting-attraction systemd[1]: networking.service: Failed with result 'exit-code'. ProblemType: Bug DistroRelease: Ubuntu 16.04 Package: ifupdown 0.8.10ubuntu1 ProcVersionSignature: User Name 4.4.0-16.32-generic 4.4.6 Uname: Linux 4.4.0-16-generic x86_64 ApportVersion: 2.20.1-0ubuntu1 Architecture: amd64 Date: Mon Apr 4 13:42:48 2016 SourcePackage: ifupdown UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1565804/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
