I'm curious about the current behavior when ovn-controller originates a
packet and transmits it over a link-local IPv6 multicast address. Will the
packet be delivered only to nodes on the same chassis, or can the packet
also reach on-link nodes on other chassis?

The reason I ask is that I'm working towards expanding OVN's IPv6 neighbor
discovery capabilities, and the first step on that path is being able to
send periodic router advertisements (RAs). In a traditional physical
network, each interface on a router may send periodic RAs to its link-local
all-nodes address (ff02::1). This way all on-link nodes receive the RA, and
the world is a happy place.

OVN is not a traditional physical router, though :)

With OVN, each hypervisor has an ovn-controller instance running, blurring
the lines about what exactly constitutes a "router interface". From an
ovn-nb point of view, a logical router port constitutes a router interface.
However, in practice, I'm not sure if this holds true once you get down to
the ovn-controller level. Let's say that a single link (via a logical
switch) is spread across three hypervisors. If the ovn-controller on each
of those hypervisors sends an RA to the link-local all-nodes address, would
that result in nodes on each hypervisor receiving three RAs? Or would each
node only receive one RA since it only receives the RA from the local

I suspect the answer to this all comes down to how openflow flows get
installed on each OVS instance. What I'm curious about is the current
behavior of OVN in this regard.

Mark Michelson

P.S. Someone please tell me if ovs-discuss would have been a more suitable
list for this question. I figured since it was related to a feature I was
developing that this would be the proper list, though.
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