Comment 101 for bug 1815989

0 packet loss is not the end goal and its not something we can ever commit too.
all we can do is try to minimise the packet loss but the variance of technology stacks and network toploiges means we can never provide a hard sla.

spiciricly qemu/libvirt don't provide any sla with regards to packetloss nor does ovs in general.
ml2/ovs and ovn its self has been enhanced to duplicate packets and send them to both the source and dest to try and cover the gap between unpasuse and network connectivity.
it uses the sending of RARP packet to trigger the disabling of the packet replication and fully activate the forwarding on the dest. i belive the window is now in the 10s of ms but its not 0 and we will likely never get to 0

we just don't control enough of the moving parts.

live migration is intended for host maintenance and we always recommend minimising the traffic to the guest when doing it if possible.

for non nfv/vnf workloads the downtime should mostly not be noticeable and TCP retansmaition will paper over it.