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why tag are created when booting vm

asked 2017-04-16 03:45:36 -0500

ashu gravatar image

updated 2017-04-16 05:51:56 -0500

Hi Team

    I'm using Openstack Newton all in one node setup using devstack on ubuntu using ml2 plugin.Whenever I'm booting Vm,the virtual interface is getting associated with vlan tag.Below is the output of ovs-vsctl show ..

           Interface patch-tun
                    type: patch
                    options: {peer=patch-int}
            Port "ni0"
                Interface "ni0"
            Port "qvo6661eb1a-fb"
                Interface "qvo6661eb1a-fb"
            Port "veth1"
                Interface "veth1"
            Port br-int
                Interface br-int
                    type: internal
            Port "qvo8c9b170b-57"
                Interface "qvo8c9b170b-57"
                tag:1
            Port "qvo07afd92c-55"
                Interface "qvo07afd92c-55"
                tag:2
        ovs_version: "2.4.1"

I want to know the actual reason for this

functionality.

Thanks
Abhishek Jain
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answered 2017-04-16 07:20:52 -0500

The tag identifies the Neutron network to which the VM is connected. If you run another VM on the same host and connected to the same network, the same tag will be used. In your example, the two ports belong to two different networks. Tags are only used inside the bridge.

If you need more detail, this is well documented in many places, for example the Redhat documentation.

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Thanks Bernd!

One more quiry.In case the Vm usses the same network to boot but on different node,will the VMs in same network but on different hosts have same tag?
ashu gravatar imageashu ( 2017-04-16 07:46:28 -0500 )edit

I think that each compute host does this independently, so that the internal VLAN tags are different, but to confirm this, I would have to investigare.

Bernd Bausch gravatar imageBernd Bausch ( 2017-04-16 08:43:37 -0500 )edit

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Asked: 2017-04-16 03:45:36 -0500

Seen: 52 times

Last updated: Apr 16 '17