On 07/12/2018 03:49 AM, Gianluca Cecchi wrote: > On Thu, Jul 12, 2018 at 4:46 AM, netsurfed <zhuohaofan@xxxxxxx > <mailto:zhuohaofan@xxxxxxx>> wrote: > > Dear all: > I start a VM with MTU size 1450, and login VM to check the mtu size, > but this setting didn't work. > > > [snip] > > > However, the actual mtu size of VM is still 1500, as following: > > root@ubuntu-zhf:~# ip addr > > > [snip] > > > 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. > > > > You have to set it inside guest OS. Not necessarily. As far back as libvirt 3.1.0, if the qemu on the host is new enough to support the "host_mtu" commandline option for network devices, the MTU setting from libvirt's XML will be visible in the device capabilities info of the device in the guest, and if the virtio-net driver in the guest is new enough, it will automatically set the MTU of the interface from the device capabilities info. > So I presume still in > /etc/network/interfaces file for Ubuntu (see also "man interfaces") Yes, if the host's qemu or the guest's virtio-net driver are not recent enough, you'll need to set it in both the guest interface config and in the libvirt XML config on the host. > See also this thread opened by me some days ago and Dominik's answer > related to new features and OVN internal dhcp server (if relevant in > your scenario) > https://lists.ovirt.org/archives/list/users@xxxxxxxxx/thread/PDIZL2GL343GFWV5L6KA4KCPARJ4HWCE/ > > HIH, > Gianluca > > > > _______________________________________________ > libvirt-users mailing list > libvirt-users@xxxxxxxxxx > https://www.redhat.com/mailman/listinfo/libvirt-users > _______________________________________________ libvirt-users mailing list libvirt-users@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvirt-users
