The numbers depend on your hardware and network topology – so you may need to experiment in your specific environment. Without large cluster I'm not sure how you can 'simulate' this as there are many factors (you could try to model it if you have all the parameters but I think it's non-trivial). I'd guess /24 is safe for most so you could start from there and move up! From: sylecn <sylecn at gmail.com<mailto:sylecn at gmail.com>> Date: Monday, April 28, 2014 7:57 PM To: Manish Godara <manishg at yahoo-inc.com<mailto:manishg at yahoo-inc.com>> Cc: "openstack-operators at lists.openstack.org<mailto:openstack-operators at lists.openstack.org>" <openstack-operators at lists.openstack.org<mailto:openstack-operators at lists.openstack.org>> Subject: Re: [Openstack-operators] Do you recommend large subnets in provider network? On Fri, Apr 25, 2014 at 12:54 AM, Manish Godara <manishg at yahoo-inc.com<mailto:manishg at yahoo-inc.com>> wrote: Yes, it's an issue if there is a large subnet (performance issues due to broadcast as well as resource issues due to number of MACs on the subnet, etc. - the severity would depend on the scale+size). Or use L3 agents/ overlay / etc. - which may have its own performance issues depending on your scale. Hi Manish, Do you have a number of just how big a subnet size is when it starts to have negative impact on the performance of the subnet? How would you benchmark network performance? Booting many VMs with significant network load is not possible since I don't have enough hardware. Is there a way to simulate and investigate the issue? -- Thanks, Yuanle -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.openstack.org/pipermail/openstack-operators/attachments/20140429/3172c09f/attachment.html>