Hello there,

In short, it's merely the name of your physical network and you can create several physical networks which are all names of your choice. Whatever name you select, needs to be used used quantum agent plugin file typically located in /etc/quantum/plugin.ini.

For exmaple:

network_vlan_ranges=physnet2:900:999 bridge_mappings=physnet1:br-ex,physnet2:br-prv integration_bridge=br-int enable_tunneling=False tenant_network_type=vlan

In this example, I have 2 physical networks, physnet1 and physnet2. physnet1 is mapped to my external bridge (br-ex) that is connected to my outside interface, while physnet2 is mapped to my private VM/Data bridge.

Then let's say a tenant creates a private VLAN, Quantum will allocate a new VLAN in the physnet2 physical network with an ID ranging from 900 to 999.

Furthermore, I want to share with you a document that I believe is the best on the net. Don't be shy to read it a few times to really understand itas it gives you an overview of how Quantum works:

http://docs.openstack.org/trunk/openstack-network/admin/content/under_the_hood_openvswitch.html

You can find more definitions at: http://docs.openstack.org/trunk/openstack-network/admin/content/provider_attributes.html