[ovs-discuss] [OVN][OpenStack] - scaling broadcast/multicast on tunnels without multicast support?

Russell Bryant russell at ovn.org
Wed Jan 13 19:14:02 UTC 2016

On 01/13/2016 02:11 PM, Guru Shetty wrote:
> On 13 January 2016 at 11:06, Kevin Benton <blak111 at gmail.com
> <mailto:blak111 at gmail.com>> wrote:
>     Hi,
>     I looked through the list and see that someone already asked about
>     multicast addresses as a target for VXLAN tunnels[1]. Since it's not
>     supported, what is the suggestion to prevent broadcast/multicast
>     traffic in a tenant's network from wiping out the network due to the
>     duplication cost?
>     This is something the current OVS plugin for Neutron in OpenStack
>     suffers from and it seems OVN will have the same issue as far as I
>     can tell.
> Assuming I understood your statement correctly, with OVN, only one
> broadcast packet goes in the tunnel and then it gets replicated in the
> hypervisor. So the load is on the CPU instead of the network.

1 copy per hypervisor, right?  meaning if a logical switch has at least
1 logical port across 100 hypervisors, it will be sent out 100 times.

>     For example, without severely rate-limiting or completely blocking
>     broadcast/multicast, a tenant network with 100 VMs on it can max out
>     a 10 Gbps interface adapter with a 100 mbps broadcast/multicast stream.
>     1. http://openvswitch.org/pipermail/discuss/2015-December/019632.html

Russell Bryant

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