Integrating OVN into the Network Fabric#

Speakers: Felix Huettner, STACKIT GmbH & Co. KG, and Frode Nordahl, Canonical

Why: The hard boundary between OVN overlays and the physical fabric — stretched L2, MAC-flapping failover, external BGP agents — is a problem anyone running OVN at DC scale hits. This is the most direct fabric/interconnect talk in the program.

What: A rearchitecture of OVN's external connectivity to replace stretched L2 with dynamic routing. A new "magic router" logical construct translates overlay L2 networks into per-chassis point-to-point networks; it is not pinned to any chassis, so egress uses ECMP across gateway chassis and ingress can enter via any of its LRPs. Failover happens by moving dynamic routes instead of MACs, so failover speed is no longer limited by routing convergence, and BFD lets the fabric pick alternate paths.

How: Work in flight includes exporting routes from OVN logical routers to Linux route tables, importing routes back in, auto-generating LRPs/LSPs per chassis (so the CMS needs no changes), and optimizing ingress/egress based on LRP locality. Route advertisement and learning via BGP, with distinct route preferences per gateway chassis and an active-active version of distributed gateway ports. A patchset ("OVN Fabric integration") is on patchwork.

Where applicable: OVN-based clouds generally — the speakers come from STACKIT (OpenStack) and Canonical, and the design supersedes the ovn-bgp-agent pattern. The stretched-L2 drawbacks it enumerates (bonding/MLAG requirements, MAC moves on failover) are universal; the fix requires upstream OVN patches that were not yet merged at talk time.