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 192.168.100.0/24.

Segment 2 with 192.168.101.0/24

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@mlavalle.com> ha scritto:

Ignazio,

You might find the following two presentations useful to understand what segments are and how they are used in routed networks:

https://www.openstack.org/videos/summits/austin-2016/mapping-real-networks-to-physical-networks-segments-and-logical-networks-in-neutron

https://www.openstack.org/videos/summits/barcelona-2016/scaling-up-openstack-networking-with-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@gmail.com> 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@gmail.com> ha scritto:

Hi,

I suppose you referenced this document:

https://docs.openstack.org/neutron/latest/admin/config-routed-networks.html

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]: https://docs.openstack.org/api-ref/network/v2/index.html?expanded=create-segment-detail#segments

Ignazio Cassano <ignaziocassano@gmail.com> 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