VM Migration Enhancements#

Speakers: Naveen Yerramneni, Nutanix (contributors: Naveen Yerramneni, Shibir Basak, Mansi Sharma, Nutanix)

Why: Live migration is where overlay networking semantics visibly break (proxy-ARP races, FDB staleness, conntrack loss) — and these are real upstream OVN features, not Nutanix-private patches.

What: New logical switch port options for migration: pkt_clone_type=mc_unknown (clone traffic to unknown ports while the destination binding is being established, fixing drops at migration start), disable_arp_nd_rsp (skip the ARP/ND responder so packets reach the port instead of being eaten by stale proxy ARP on the source), force_fdb_lookup (learn a port's additional MACs through OVN's native FDB, avoiding packet duplication when combined with cloning), and disable_garp_rarp. Plus FDB cleanup on port down, and controller CT-zone reservation (external_ids:reserve_ct_zones) so conntrack entries can be synchronized during migration — the latter two patches under review at talk time.

How: Each option targets a specific drop scenario demonstrated across a VXLAN-extended subnet spanning availability zones.

Where applicable: OVN generally (upstream options); the cross-AZ migration topology is Nutanix's use case, but the failure modes are universal to any live migration over OVN.