Re: Could you please help with questions about the net failover feature

On 3/21/20 1:08 AM, Yalan Zhang wrote: There is only one hostdev device in the team pair (that will be the one with <teaming type='transient'.../> since it needs to be unplugged during migration). The other device must be a virtio device (the one with <teaming type='persistent'/>). And no, they cannot be on different subnets. They must both connect into the same ethernet "collision domain", such that the guest could assign the same IP address to either of them and be able to communicate on the network. There is some explanation of the use case for this option. and some example config, here: https://www.libvirt.org/formatdomain.html#elementsTeaming No, not right :-) The VF of an SRIOV network adapter is connected directly to the physical network, and will have an IP address that is on that network. Tap devices plugged into the default network (or any other libvirt network based on a bridge device that is created/managed by libvirt) have no direct connection to the physical network, and are on a different subnet. The fact that traffic from the guest *seems* to be coming from an IP on the physical subnet is meaningless. The *guest* needs to be able to use both NICs using the same IP address, and anything plugged into the default network will need to have an IP address on a different subnet from the perspective of the guest. You have two choices for the backup virtio interface: 1) it can be a macvtap device connected to the PF of the same SRIOV device. 2) it can be a standard tap device connected to a Linux host bridge (created outside libvirt in the host system network config) that is attached to the PF (or alternately one of the VFs that isn't being used for VMs, or to another physical ethernet adapter on the host that is connected to the same network. It is simplest to have the same name refer to the connection on the source and destination hosts of a migration. That can be handled by creating a libvirt network to refer to the bridge device created outside libvirt (or to the PF directly if you're going to use macvtap. For example, if you're going to use macvtap, and the PF's name on the host is ens4f0, you'd just create this network: <network> <name>persistent-net</name> <forward mode='bridge'> <interface dev='ens4f0'/> </forward> <network> any guest interface with this: <interface type='network'> <source network='persistent-net'/> <mac address='00:11:22:33:44:55'/> <model type='virtio'/> <teaming type='persistent'/> <alias name='ua-backup0'/> </interface> will get a macvtap device that's connected to ens4f0 in bridge mode. Or, if your host has a bridge device called br0 that is directly attached to the physical network (in whatever manner, it doesn't matter), you can define the network this way: <network> <name>persistent-net</name> <bridge name='br0'/> <forward mode='bridge'/> <network> The XML for the guest interface would be the same. Then for the vfio (transient) interface, you could also define a network: <network> <name>transient-net</name> <forward mode='hostdev'> <pf dev='ens4f0'/> </forward> </network> and instead of using <interface type='hostdev'> in the guest config, you would use this: <interface type='network'> <source network='transient-net'/> <model type='virtio'/> [1] <mac address='00:11:22:33:44:55'/> <teaming type='transient' persistent='ua-backup0'/> </interface> Even if the device names change on the other host (the destination of the migration), as long as the other host has networks named "persistent-net" and "transient-net" that are of similar types (macvtap or bridged for persistent-net, and hostdev for transient-net) then libvirt will be able to migrate the guest from one host to the other with no mangling of the XML required.