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Bob,

Thanks for your detailed response. In it you "strongly recommend that any
functionality trying to make decisions based on connectivity do so by
calling into the registered mechanism drivers, so they can decide whether
whatever they manage has connectivity". After eading this I went through
the mechanism driver API definition (currently at
http://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2/driver_api.py#n549).
The only method and the API that seems to be useful to implement your
recommendation is  filter_hosts_with_segment_access (currently at line
914). Is this method the right way to go?

Thanks

Miguel

On Tue, Mar 29, 2016 at 4:47 PM, Robert Kukura <kukura at noironetworks.com>
wrote:

> My answers below are from the perspective of normal (non-routed) networks
> implemented in ML2. The support for routed networks should build on this
> without breaking it.
>
> On 3/29/16 3:38 PM, Miguel Lavalle wrote:
>
> Hi,
>
> I am writing a patchset to build a mapping between hosts and network
> segments. The goal of this mapping is to be able to say whether a host has
> access to a given network segment. I am building this mapping assuming that
> if a host A has a bridges mapping containing 'physnet 1' and a segment has
> 'physnet 1' in its 'physical_network' attribute, then the host has access
> to that segment.
>
> 1) Is this assumption correct? Looking at method check_segment_for_agent
> in
> http://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2/drivers/mech_agent.py#n180
> seems to me to suggest that my assumption is correct?
>
> This is true for certain agent-based mechanism drivers, but cannot be
> assumed to be the case for all mechanism drivers (even all those that use
> agents. Any use of mapping info (i.e. from agents_db or elsewhere) is
> specific to an individual mechanism driver. I'd strongly recommend that any
> functionality trying to make decisions based on connectivity do so by
> calling into the registered mechanism drivers, so they can decide whether
> whatever they manage has connectivity.
>
> Also note that connectivity may involve hierarchical port binding, in
> which case you really need to try to bind a port to determine if you have
> connectivity. I'm not suggesting that there is a requirement to mix HPB and
> routed networks, but please try not to build assumptions into ML2 plugin
> code that don't work with HPB or that are only valid for a subset of
> mechanism drivers.
>
>
> 2) Furthermore, when a segment is mapped to a physical network, is there a
> one to one relationship between segments and physical nets?
>
> Certainly different virtual networks can map to different segments (i.e.
> VLANs) on the same physical network. It is even possible for the same
> virtual network to have multiple segments on the same physical network.
>
> -Bob
>
>
> Thanks
>
>
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