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VXLAN port not open in Hyper-V

asked 2017-02-24 15:17:26 +0300

roli gravatar image

updated 2017-02-26 12:31:50 +0300


I'm trying to get instances in a Windows Server 2016 Datacenter based Hyper-V compute node to communicate with instances on other hypervisors using Open vSwitch and neutron-ovs-agent over VXLAN. My other hypervisors run CentOS/KVM. Instances on the Linux machines can communicate just fine, but I don't get the ones running in Hyper-V to communicate with the world outside the hypervisor.

The setup runs two controller nodes ( and with a shared VIP with the L3-agent running the router on .21. In addition I have two separate hypervisors installed, one KVM ( and one Hyper-V (

The Hyper-V host runs 3 VMs, one CirrOS ( and two Windows Server (one with and one trying to use DHCP).

I have created a Hyper-V VMswitch named "external" and enabled the Open vSwitch extension. The VMswitch is connected to a physical interface named "Tenant" (without IP). I have also manually created a Open vSwitch bridge named "br-ex" and connected the "Tenant" port above to it. The hypervisor also has a Management interface with IP (i.e. with connectivity to the other Openstack nodes, this is the interface that should be used for the VXLAN traffic.

The VMs on Hyper-V can ping themselves and other VMs on the same Hyper-V host. They can not access the router, DHCP-server on the controller node or VMs on other hypervisors.

I think the problem has something to do with that Open vSwitch does not open a listening socket for VXLAN (udp/4789), i.e. according to netstat -na | find "4789". I also can see outgoing flood traffic from br-tun to each VXLAN port according to ovs-ofctl dump-flows br-tun but I don't see this traffic in wireshark or at the incoming br-tun VXLAN port on the other hypervisors, my guess is that this is outgoing ARP requests that for some reason are not sent out on the physical interface.

If I try to connect to an instance on the Hyper-V host from the outside ( I see the incoming TCP SYN on the Hyper-V host (but not on the VM).

Frame 1195965: 128 bytes on wire (1024 bits), 128 bytes captured (1024 bits) on interface 0
Ethernet II, Src: HewlettP_70:57:80 (ac:16:2d:70:57:80), Dst: HewlettP_70:a9:d0 (ac:16:2d:70:a9:d0)
Internet Protocol Version 4, Src:, Dst:
User Datagram Protocol, Src Port: 44982, Dst Port: 4789
Virtual eXtensible Local Area Network
Ethernet II, Src: fa:16:3e:e2:06:b1 (fa:16:3e:e2:06:b1), Dst: fa:16:3e:9e:f7:c6 (fa:16:3e:9e:f7:c6)
Internet Protocol Version 4, Src:, Dst:
Transmission Control Protocol, Src Port: 53839, Dst Port: 22, Seq: 0, Len: 0

I.e ... (more)

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Hi, Thanks for adding the detail information about your setup. To be short the problem is you are missing flows for br-ex, which means it will drop all the packets. A simple way to fix this is: ovs-ofctl del-flows br-ex ovs-ofctl add-flow br-ex actions=normal.

aserdean gravatar imageaserdean ( 2017-02-26 16:36:03 +0300 )edit

Please remove: the following lines from your neutron config: vxlan_group = bridge_mappings = physnet1:br-ex Try to follow the steps described in the blog post: . That should get you up to speed. Thanks, Alin.

aserdean gravatar imageaserdean ( 2017-02-26 16:37:59 +0300 )edit

Thanks for your quick response. I tried removing vxlan_group = and bridge_mappings = physnet1:br-ex. But still it will not open a UDP/4789 listening port for VXLAN. I suppose that will be needed?! Any idea what could be the cause of this?

roli gravatar imageroli ( 2017-02-26 18:59:01 +0300 )edit

I also tried adding the normal flow to br-ex. I no longer get any drops there. I will try to redo the installation according to the url provided, when I'm back in office and let you know the results.

roli gravatar imageroli ( 2017-02-26 19:00:44 +0300 )edit

Ok, did your prior env work though?. You won't see anyone listening on the udp port we sniff the packets directly in the datapath.

aserdean gravatar imageaserdean ( 2017-02-27 13:21:47 +0300 )edit

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answered 2017-02-28 14:33:26 +0300

aserdean gravatar image

Ah now I see the problem. On windows we require that you add the tunnel interface to OVS (the interface). Please enable the adapter: br-ex and set the local ip to it:

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Asked: 2017-02-24 15:17:26 +0300

Seen: 1,222 times

Last updated: Feb 26 '17