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https://issues.apache.org/jira/browse/CLOUDSTACK-6757?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14113456#comment-14113456
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Murali Reddy commented on CLOUDSTACK-6757:
------------------------------------------

Problem;
-----------
GRE tunnel networks are internal networks in XenServer. A XenServer network 
created on a XenServer, is visible across the hosts in the clusters. Only on 
the first host on which a VM is launched there is a bridge created 
automatically. When a VM is launched on a different host in the cluster, but on 
the same network, VM start will fail with VM_REQUIRES_NETWORK exception as 
bridge is not automatically created by the Xenserver. To overcome this issue, 
there is a hack put into CloudStack, so that bridge is create for internal 
network that is backing GRE tunnel network. A vif is created on to the network 
and plugged in to dom0 which will result in the bridge getting created. This 
bug describes the scenario where the VIF's created on dom0 are not getting 
deleted when a network is deleted.

Root Cause Analysis:
--------------------------
Root cause is using the dom0 vif connected to a GRE tunnel network as a forcing 
function to create bridge on the host. this VID is never deleted even when a 
network object created on XenServer is deleted.

Proposed Solution:
------------------------
Proposed solution is to get rid of the hack the use vif connected to dom0 as a 
forcing function to create bridge. With the fix in CLOUDSTACK-6925, we no 
longer need dom0 vif.

QA steps:
-------------

CLOUDSTACK-6925: actually fixes the use dom0 VIF issue. With CLOUDSTACK-6925, 
there is no longer any vif''s are connected to dom0. Please ensure when GRE 
tunnel network is created there is no VIF that gets plugged into dom0.

> [OVS] Deleting networks does not unplug nics from dom0 on xenserver
> -------------------------------------------------------------------
>
>                 Key: CLOUDSTACK-6757
>                 URL: https://issues.apache.org/jira/browse/CLOUDSTACK-6757
>             Project: CloudStack
>          Issue Type: Bug
>      Security Level: Public(Anyone can view this level - this is the 
> default.) 
>          Components: Management Server, Network Controller, XenServer
>    Affects Versions: 4.4.0
>         Environment: Latest build from 4.4 with commit 
> e6961fd21bb6d793302c234d0f409f66dc498072
>            Reporter: Sanjeev N
>            Assignee: Murali Reddy
>            Priority: Critical
>              Labels: DEV_REVIEWED, ovs
>             Fix For: 4.4.0
>
>
> [OVS] Deleting networks does not unplug nics from dom0 on xenserver
> Steps to reproduce:
> ================
> 1.Bring up CS in advanced zone with xen cluster
> 2.Create physical network with GRE isolation
> 3.Create network offering with virtual networking and ovs as the service 
> provider
> 4.Create couple of guest networks with above network offering
> 5.Deploy few vms in each network
> 6.Delete the guest networks
> Expected Result:
> ==============
> When CS creates tunnel networks it plugs a vif on dom0 for every tunnel 
> tunnetwork. However it does not unplug the vif from dom0 even-though the 
> network is deleted.
> Observations:
> ===========
> We can see that bridge is getting deleted from the host bug the vif is not 
> getting unplugged from dom0.
> Attaching MS log file. Please look for bridge named "OVSTunnel989" in the log 
> file.



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