Open Stack

> We already have many different vlans, one for each department. Some of them have public ip networks and some private networks.
> For instance when a department ask for a virtual server we run it in our IP network,
> when if we were using vlans in xen we could run it on the departments network lets say vlan 3.
> what we want is to use this vlans we already have assigned to each department in our openstack deploy

Juan,

You can use the bridge-mapped network in Quantum to do this.
This will create a network in openstack which is mapped to a physical network/vlan.
So if basically create a network for each tenant with its own vlan mapping to the appropriate network.

This link might help you setting things up:
https://wiki.openstack.org/wiki/ConfigureOpenvswitch

I think you can also do this with the "old-style" networking without quantum/openvswitch.
If you have the time I would invest it in Quantum though, it adds a lot of flexibility and as long as you are still in the setup phase you have some time to play around with it :) 

Cheers,
Robert van Leeuwen