[openstack-dev] [Neutron]Relationship between physical networks and segment

Neil Jerram Neil.Jerram at metaswitch.com
Wed Mar 30 14:49:15 UTC 2016

On 29/03/16 20:42, Miguel Lavalle wrote:
> Hi,

Hi Miguel,

> 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?

Yes, I would say so.  In other words: if a host can access a particular 
physical network, it can access all segments that use that physical network.

> 2) Furthermore, when a segment is mapped to a physical network, is there
> a one to one relationship between segments and physical nets?

No; I would say that segments are N:1 with physical networks, with VLANs 
being the most obvious example.


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