Open Stack

Thanks for this clarification. 
Just wondering: Do multiple network nodes (router + dhcp) help to exceed
the 4k subnet limitation? In such a scenario, will dhcp + routing be
distributed or is a second network node just something like a
hot-standby?

Thanks!

-- 
Andreas 
(irc: scheuran)


On Thu, 2014-09-18 at 09:47 -0400, George Mihaiescu wrote:
> The VLAN ID is only locally significant to each compute node, so same
> subnet belonging to same tenant could would have different VLAN tags
> on different compute nodes.
> 
> VLAN tag 1 could be used by subnet1 of tenant A on node1 and by
> subnet1 of tenant B on node 2, with no conflicts.
> 
>  
> 
> Both VXLAN and GRE add a 24-bit header, so the maximum number of
> tunnels is 16 million but each compute node can locally implement only
> a maximum of 4096 different neutron subnets.
> 
> What are the chances that you have more than 4096 instances on a
> compute node, each connected to a different neutron subnet?
> 
> What are the chances that you have more than 409 instances on a
> compute node, each connected to 10 different neutron subnets?
> 
>  
> 
> The same limitation applies to the Neutron node (because a tunnel
> endpoint exists there as well), so you cannot have a Neutron node
> where a L3 agent and a DHCP agent serve more than 4096 Neutron
> subnets, but you would hit other limits by then.
> 
>  
> 
> George
> 
>  
> 
>                                    
> ______________________________________________________________________
> From: BYEONG-GI KIM [mailto:kimbyeonggi at gmail.com] 
> Sent: Wednesday, September 17, 2014 10:41 PM
> To: George Mihaiescu; openstack at lists.openstack.org
> Subject: Re: [Openstack] Question about VXLAN support
> 
> 
>  
> 
> Dear George
> 
>  
> 
> 
> Thank you for the reply. 
> 
> 
>  
> 
> 
> I'm a little confused about your reply. 
> 
> 
>  
> 
> 
> Can be the same tag number assigned to different tenant? For example,
> I assume the situation where a subnet 1 assigned tag number 1 and it
> belongs to tenant A, and a subnet b is also assigned tag number 1 and
> it belongs to tenant B. Or, should be the tag number different even if
> subnets belong to different tenant?
> 
> 
>  
> 
> 
> If the later case, the tag number seems much more strictly limited,
> because a tenant can have many subnet. If a subnet has 10 subnets,
> which means 10 tag numbers must be assigned, the openstack only create
> about 400 tenants.
> 
> 
>  
> 
> 
> Is the VXLAN network type in OpenStack really scalable comparing with
> VLAN or GRE? Or does the current OpenStack just provide functionality
> to handle VXLAN header?
> 
> 
>  
> 
> 
> Please let me know good example about VXLAN usage, which can provide
> scalability for multi-tenant on OpenStack. I'd like to know whether
> more than 100000 tenants could be handled by VXLAN on the latest
> OpenStack implementation or not.
> 
> 
>  
> 
> 
> Best regards
> 
> 
>  
> 
> 
> Byeong-Gi KIM
> 
> 
>  
> 
> 2014-09-18 11:20 GMT+09:00 George Mihaiescu <George.Mihaiescu at q9.com>:
> 
> The internal VLAD ID is indeed limited to 4096 but this internal tag
> number is used to isolate different neutron subnets, not tenants. 
> 
> A tenant could create 10 neutron networks each with its own subnet and
> then start 10 instances each attached to a separate net/subnet. If
> these instances would be scheduled on the same compute node then they
> would all use different internal VLAN IDs (locally unique to that
> node).
> 
>  
> 
> Basically, you’re right that there is a built-in limitation of 4096
> instances attached to 4096 different Neutron net/subnets on a compute
> node, but it’s not realistic to actually start that many instances on
> a compute node.
> 
>  
> 
> George
> 
>  
> 
>  
> 
>                                    
> ______________________________________________________________________
> From: BYEONG-GI KIM [mailto:kimbyeonggi at gmail.com] 
> Sent: Wednesday, September 17, 2014 8:47 PM
> To: openstack at lists.openstack.org
> Subject: [Openstack] Question about VXLAN support
> 
> 
>  
> 
> Hello.
> 
>  
> 
> 
> I have a question about the VXLAN support on OpenStack.
> 
> 
>  
> 
> 
> As far as I know, the OVS operates like the below:
> 
> 
>  
> 
> 
> 1. A tag number is created to identify each tenant, and it is used
> between br-int and br-tun. Furthermore the tag number is identified as
> a VLAN ID (I checked it via tcpdump).
> 
> 
>  
> 
> 
> 2. After the packet arrived at br-tun, it is encapsulated and VNI
> (VXLAN Network Identifier) is attached. The binding information
> between the VLAN ID (tag number) and the VNI is stored in OVSDB. 
> 
> 
>  
> 
> 
> If the operation is correct, it seems that the number of tenants which
> can be created is still limited to about 4000, which is the supported
> range of VLAN, because the tag number is used to identify each tenant
> at the inside of br-int regardless of the supported range of VNI. 
> 
> 
>  
> 
> 
> If more than 5000 tenants are created in a Compute Node, how could be
> these identified after the packet arrived at br-int? In the theory,
> the 4500th tenant should have 4500 tag number but the tag number is
> presented as VLAN ID so that it cannot be assigned over 4096.
> 
> 
>  
> 
> 
> Any advice and comment would really be appreciated.
> 
> 
>  
> 
> 
> Best regards
> 
> 
>  
> 
> 
> Byeong-Gi KIM
> 
> 
>  
> 
> 
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