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GRE Tunnels and VLANs on OVS

Asked by Doug

Very simple question. I used this guide to install folsom: http://docs.openstack.org/folsom/basic-install/content/basic-install_intro.html. I am not using namespaces. I am using the gre tenant_network_type. The interface that dnsmasq hands out ip addresses on, and the gateway interface that the vm uses to leave the subnet, are in completely different vlans than any of the vm interfaces on the ovs on the compute node. I made an entry here: http://visualne.wordpress.com/2013/02/09/quantum-gre-tunnels-ovs/. I guess my question is, do the gateway and dnsmasq interface need to be in the same vlan as the vm interface?

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  • by Doug
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GMi (gmi) said : 		#1

The VLAN ID you see in the output of "ovs-vsctl show" are only locally significant and they are not really layer 2 tags added to the frames leaving on the physical interface.
They are only used by openvswitch to separate traffic on the br-int, so the different tap interfaces corresponding to different quantum subnets do not see each other's traffic.

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Doug (dsmith4546) said : 		#2

Thanks GMi, that solved my question.

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Doug (dsmith4546) said : 		#3

I guess I need to understand ovs a little better. How do two ovs's connected together with a gre tunnel know what to do with a broadcast frame from a particular vlan? How does the ovs make a layer 2 decision if the frame isn't tagged with a vlan id?

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GMi (gmi) said : 		#4

If you take a look at the flows (defined and learned) by the openvswitch, you will see get a better understanding of how openvwitch operates.

Use the following commands to see the flows:

ovs-appctl bridge/dump-flows br-int
ovs-dpctl dump-flows br-int

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