[neutron] Shared tenant network allow duplicate IP's?

Jeremy Stanley fungi at yuggoth.org
Wed Feb 26 22:07:53 UTC 2020

On 2020-02-26 13:26:43 -0800 (-0800), Dan Sneddon wrote:
> That has never been supported. It is not feasible to have two VMs on the
> same network+subnet that have the same IP, even if they are owned by
> different tenants. That isn't a Neutron limitation, that's a limitation of
> IP-over-Ethernet that applies to all networks.
> Think of the non-virtualized equivalent, if you had a physical network
> subnet with two computers using the same IP address there would be a
> conflict, even if one computer was owned by Alice and the other computer
> was owned by Bob. There is no way to make that work in a virtualized cloud
> environment unless the two tenants are using different network subnets.

It's probably useful to level-set on terminology, since not all
these same words are used to mean the same things in different
contexts. From Neutron's perspective "network" is your OSI layer 2
broadcast domain, and "subnet" is your OSI layer 3 addressing.
Obviously to reuse the same layer 3 (IP) addresses on different
systems you need them to reside on separate layer 2 (Ethernet)
networks and have independent routing, most likely with some layer 3
address translation in place if they are ever expected to
communicate with one another.

As Dan points out, though, this has nothing to do with multi-tenancy
and everything to do with the fundamentals rules of network
Jeremy Stanley
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