Openstack routed provider network

Ignazio Cassano ignaziocassano at
Sat Jul 30 18:51:41 UTC 2022

Hello, sorry but my networking skill is very poor.
Let me do explain what I understood
With routed provider network I can use a single provider network to
represent multiple l2 networks.
For example use case 1:
Compute node A on vlan 100.
Compute node B on vlan 100.
I can create more then one segments on vlan 100 with different cidr.
Segment 1 with
Segment 2 with

Use case case 2:
 I can also have nodes on different  vlan and using aggregates to address
vm on compute nodes depending on ip address.
Compute node A and B on vlan 100.
Compute node C and D on vlan 101.
Vm on segments belonging to vlan 100 are addressed on Cimpute node A or B.
Vm on segments belonging to vlan 101 are addressed on compute node C or D.

In both use case phisical router must be configured because openstack
virtual router cannot be used.
Please, let me know if I undertood well.

Il Mer 27 Lug 2022, 16:50 Miguel Lavalle <miguel at> ha scritto:

> Ignazio,
> You might find the following two presentations useful to understand what
> segments are and how they are used in routed networks:
> And to summarize what you will find in those presentations:
> 1) A segment is a single L2 broadcast domain, be it a vlan or a vxlan or
> any other way to realize a L2 broadcast domain in the networking fabric.
> 2) A Neutron network can be created stitching together 1 or several
> segments. If after putting several segments together in a Neutron network
> they become a single L2 broadcast domain (i.e. they are stitched together
> via switching) then you have a multi-segment Neutron network. However ....
> 3) If the segments in a Neutron network are stitched together with L3
> routers, then you have a routed provider network. In such networks, each
> segment is a separate L2 broadcast domain, which should provide higher
> levels of scalability
> 4) To better understand the terminology, you may also find it useful to
> understand the distinction between  "provider networks" and "tenant
> networks". A provider network is one that was mapped explicitly at creation
> by a cloud admin to specific segments, most likely to achieve certain
> performance / scalability goals. A tenant network is one for which, at
> creation, Neutron assigned automatically a segment
> Best regards
> Miguel
> On Wed, Jul 27, 2022 at 3:01 AM Ignazio Cassano <ignaziocassano at>
> wrote:
>> Hello, thanks for your reply.
>> The segment id is the vlan id  (in your example 101) ?
>> My understanding is that  some compute nodes in a rack are connected to a
>> vlan, and other on another vlan.
>> Then I can create a network (segmentation1) and scheduler put the vm on
>> the compute node where vlan is present.
>> So for users exists only segmentaion1 network and they do not know it is
>> splitted in more vlans.
>> Is it correct ?
>> Ignazio
>> Il giorno mer 27 lug 2022 alle ore 09:27 Lajos Katona <
>> katonalala at> ha scritto:
>>> Hi,
>>> I suppose you referenced this document:
>>> In Neutron terminology segments appear on different layers, on the API a
>>> segment is a network type / seg. id / phys-net / net uuid tuple (see [1]).
>>> What is interesting here that this segment has to be a representation on
>>> the compute where l2-agent (ovs-agent) can know which segment is the one it
>>> can bind ports.
>>> That cfg option is in ml2_conf.ini, and bridge_mappings, where the
>>> admin/deployer can state which bridge (like br-ex) is connected to which
>>> provider network (out of Openstack's control).
>>> So for example a sample config in ml_conf.ini like this:
>>> bridge_mappings = public:br-ex,physnet1:br0
>>> Means that on that compute VM ports can be bound which has a network
>>> segment like this: ( network_type: vlan, physical_network: *physnet1*, segmentation_id:
>>> 101, network_id: 1234-56..)
>>> More computes can have the same bridge-physnet mapping, the deployer's
>>> responsibility is to have these connected to the same switch, whatever.
>>> [1]:
>>> Ignazio Cassano <ignaziocassano at> ezt írta (időpont: 2022.
>>> júl. 26., K, 21:04):
>>>> Hello All, I am reading documentation about routed provider network.
>>>> It reports: "
>>>> Routed provider networks imply that compute nodes reside on different
>>>> segments. "
>>>> What does mean ?
>>>> What is a segment it this case ?
>>>> Thanks for helping me"
>>>> Ignazio
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