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[6]http://archive.openflow.org/wp/learnmore/

[7]http://openvswitch.org/cgi-bin/ovsman.cgi?page=vswitchd%2Fovs-vswitchd.8#LIMITS

Scope

• scope of this proposal is restricted to achieving distributed routing and network acl's with OpenVswitch
• scope of this proposal is restricted to OpenVswtich integration on XenServer/KVM 

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Performance and scaling issues

• For distributed routing there is a logical router created and bridge for each tier irrespective of the fact VM from tier is running on hypervisors or not. Given that current hypervisors can run VM's in the magnitude of hundreds clearly for the proposed distributed routing solution require creating bridges in same magnitude in the worst case. Maximum number of switches that can be supported by OpenVswitch depends on the maximum number of file descriptors configured [7]. So maximum number of bridges that can be created on hypervisor should not be a concern.
• Maximum
• number of switches that can be supported on a hypervisor
• number of flows that can applied to a switch is only limited by memory available. There is no hard limit on the maximum number of flows that can be configured on a switch.

Open Issues

• Effort of setting up full tunnel mesh for all the tiers in the VPC when first VM from a VPC gets launched on a host can be expensive operation. Alternative option could be first setup the logical router and bridges with full mesh tunnels then add flow rule switch subnet traffic to be sent over patch port to logical router. 
• dealing with disconnected hosts while creating tunnels