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Hi Marco,

At least two of your questions clearly hint at the dichotomy between subnet
and network, which appear to be redundant.
A multi-homing use case on a single network is a potential use case for
this, albeit a very limited one, since one might argue that in a cloud
scenario instead of allocating two IPs from two different subnets on a NIC
one would rather have two NICs with one IP each.

I agree that perhaps in 99% of cases there's no need for separating this
two concepts. Automatically provisioning a network when a subnet with no
network id is created is something which might be considered.
In my opinion, a reason for which the network/subnet concept are separated
is for allowing either L2-only and L2/L3 use cases. For instance, with
L2-only you might have Neutron provisioning your networks and then either
no IP configuration at all, or some other service doing IP configuration.

On a separate note, exhaustion of the VLAN pool is very likely in cloud
deployments. There is a hard limit given the 12-bit size of the VLAN
identifier. Also, if switches are not trunked and VLANs are provisioned
there too, there might be a further limitation on the number of VLANs which
can be configured on each switch port. But please don't trust me when it
comes to networking appliances, as I have a rather limited knowledge on the
subject.

Salvatore


On 14 October 2013 09:01, Yongsheng Gong <gongysh at unitedstack.com> wrote:

>
>
>
> On Mon, Oct 14, 2013 at 2:55 PM, Marco Fornaro <Marco.Fornaro at huawei.com>wrote:
>
>>  Hi Gong,****
>>
>> ** **
>>
>> Thanks so much for your answers****
>>
>> ** **
>>
>> Just one more question: you wrote “You can create networks with just one
>> subnet, but the vlan id will run out soon if vlan is used.”****
>>
>> Sorry but: how can the Vlan ID “run out soon”?...is it really possible to
>> finish them?****
>>
>> **
>>
> for example, one network is using one vlan ID if vlan is used for linux
> bridge plugin. If we create networks with just one subnet, we will need
> more vlan ids than networks with more than subnets.
>
>
>>
> **
>>
>> Best Regards****
>>
>> ** **
>>
>> Marco****
>>
>> ** **
>>
>> ** **
>>
>> *From:* Yongsheng Gong [mailto:gongysh at unitedstack.com]
>> *Sent:* den 11 oktober 2013 10:56
>> *To:* OpenStack Development Mailing List
>> *Subject:* Re: [openstack-dev] Tricky questions - 1/2 Quantum Network
>> Object****
>>
>> ** **
>>
>> ** **
>>
>> ** **
>>
>> On Fri, Oct 11, 2013 at 4:41 PM, Marco Fornaro <Marco.Fornaro at huawei.com>
>> wrote:****
>>
>> Hi All,****
>>
>>  ****
>>
>> (I already posted this on openstack mail list, but perhaps it’s more a
>> developer stuff J)****
>>
>> Some Tricky questions I ask help for (email 1 of 2):****
>>
>>  ****
>>
>>  ****
>>
>> *Quantum Network object*****
>>
>> In the “openstack networking guide”->”Using Openstack compute with
>> Openstack”->” Advanced VM creation” (
>> http://docs.openstack.org/grizzly/openstack-network/admin/content/advanceed_vm_creation.html)
>> there are example boot a VM on one or more NETWORKs (meaning the quantum
>> Network object):  ****
>>
>> nova boot --image <img> --flavor <flavor> \****
>>
>> *--nic net-id=<net1-id> --nic net-id=<net2-id>* <vm-name>****
>>
>>  ****
>>
>> BUT if you look at the description of the network object in the API
>> abstraction it looks like a collection of subnets (meaning the quantum
>> object), so basically a collection of IP Addresses like 192.168.100.0/24*
>> ***
>>
>>  ****
>>
>> *SO (first question): what happens in the network where I boot the VM
>> has more than a subnet?...I suppose the VM should have a nic for EACH
>> subnet of the network!*****
>>
>> You will just get a nic for each network, not for each subnet of the
>> network.   to choose the subnet, use --nic
>> net-id=net-uuid,v4-fixed-ip=ip-addr****
>>
>>   ****
>>
>> *THEN (second question): why do I need a network object? Shouldn’t it be
>> more practical to have just the subnet object?..why do I need to create a
>> Network if it’s just a collection of subnets?*****
>>
>>  under the hood, the traffic among networks are isolated by tunnel id,
>> vlan id or something else. You can create networks with just one subnet,
>> but the vlan id will run out soon if vlan is used.****
>>
>> ** **
>>
>> we can have many networks, and the subnets within network can have
>> overlap IPs.****
>>
>> ** **
>>
>>   ****
>>
>> Thanks in advance for any help****
>>
>>  ****
>>
>> Best Regards****
>>
>>  ****
>>
>> Marco****
>>
>>  ****
>>
>>  ****
>>
>>  ****
>>
>>
>> _______________________________________________
>> OpenStack-dev mailing list
>> OpenStack-dev at lists.openstack.org
>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev****
>>
>>  ** **
>>
>
>
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