Dear all:
I start a VM with MTU size 1450, and login VM to check the mtu size, but this setting didn't work.
The VM xml is like this:
<interface type='bridge'>
<mac address='52:54:00:54:14:f8'/>
<source bridge='ovsbr1'/>
<virtualport type='openvswitch'>
<parameters interfaceid='a42e5b42-09db-4cfa-b198-d2ce62843378'/>
</virtualport>
<target dev='vnet0'/>
<model type='virtio'/>
<mtu size='1450'/>
<alias name='net0'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
</interface>
However, the actual mtu size of VM is still 1500, as following:
root@ubuntu-zhf:~# ip addr
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 52:54:00:54:14:f8 brd ff:ff:ff:ff:ff:ffThe MTU size of both ovs bridge and vnet are 1450 in my hypervisor:
root@ubuntu-191:~# ip addr show ovsbr1
16: ovsbr1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN group default qlen 1
link/ether 12:01:7b:5b:85:49 brd ff:ff:ff:ff:ff:ff
inet6 fe80::1001:7bff:fe5b:8549/64 scope link
valid_lft forever preferred_lft forever
root@ubuntu-191:~# ip addr show vnet0
22: vnet0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc pfifo_fast master ovs-system state UNKNOWN group default qlen 1000
link/ether fe:54:00:54:14:f8 brd ff:ff:ff:ff:ff:ff
inet6 fe80::fc54:ff:fe54:14f8/64 scope link
valid_lft forever preferred_lft forever
I use ovs to create vxlan networks and add VMs to the ovs bridge. Because of the limitations of vxlan, I need to set the mtu of vm to 1450.
How to set the MTU of VM? Thanks.
Below some information about my hypervisor:
root@ubuntu-192:~# virsh -V Virsh command line tool of libvirt 3.4.0 See web site at http://libvirt.org/ Compiled with support for: Hypervisors: QEMU/KVM LXC UML OpenVZ VMware VirtualBox Test Networking: Remote Network Bridging Interface udev Nwfilter VirtualPort Storage: Dir Filesystem SCSI Multipath iSCSI LVM Miscellaneous: Daemon Nodedev SELinux Secrets Debug Modular
root@ubuntu-192:~# qemu-x86_64 --version qemu-x86_64 version 2.9.0 Copyright (c) 2003-2017 Fabrice Bellard and the QEMU Project developers
root@ubuntu-192:~# uname -a Linux ubuntu-192 4.4.0-62-generic #83-Ubuntu SMP Wed Jan 18 14:10:15 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
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