[openstack-dev] [Neutron] Segments, subnet types, and IPAM

Carl Baldwin carl at ecbaldwin.net
Fri Mar 11 23:15:16 UTC 2016


I have started to get into coding [1] for the Neutron routed networks
specification [2].

This spec proposes a new association between network segments and
subnets.  This affects how IPAM needs to work because until we know
where the port is going to land, we cannot allocate an IP address for
it.  Also, IPAM will need to somehow be aware of segments.  We have
proposed a host / segment mapping which could be transformed to a host
/ subnet mapping for IPAM purposes.

I wanted to get the opinion of folks like Salvatore, John Belamaric,
and you (if you interested) on this.  How will this affect the
interface to pluggable IPAM and how can pluggable implementations can
accommodate this change.  Obviously, we wouldn't require
implementations to support it but routed networks wouldn't be very
useful without it.  So, those implementations would not be compatible
when routed networks are deployed.

Another related topic was brought up in the recent Neutron mid-cycle.
We talked about adding a service type attribute to to subnets.  The
reason for this change is to allow operators to create special subnets
on a network to be used only by certain kinds of ports.  For example,
DVR fip namespace gateway ports burn a public IP for no good reason.
This new feature would allow operators to create a special subnet in
the network with private addressing only to be used by these ports.

Another example would give operators the ability to use private
subnets for router external gateway ports if shared SNAT is not needed
or doesn't need to use public IPs.

These are two ways in which subnets are taking on extra
characteristics which distinguish them from other subnets on the same
network.  That is why I lumped them together in to one thread.


More information about the OpenStack-dev mailing list