Openstack routed provider network

Miguel Lavalle miguel at
Sun Jul 31 17:13:32 UTC 2022

You got it!

On Sat, Jul 30, 2022 at 1:51 PM Ignazio Cassano <ignaziocassano at>

> 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.
> Ignazio
> 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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