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 <gong...@unitedstack.com> wrote: > > > > On Mon, Oct 14, 2013 at 2:55 PM, Marco Fornaro > <marco.forn...@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:gong...@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.forn...@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@lists.openstack.org >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev**** >> >> ** ** >> > > > _______________________________________________ > OpenStack-dev mailing list > OpenStack-dev@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > >
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