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Bug 1570834

Summary: OVN limitations when using VLAN tenant/provider networks
Product: Red Hat OpenStack Reporter: Daniel Alvarez Sanchez <dalvarez>
Component: documentationAssignee: RHOS Documentation Team <rhos-docs>
Status: CLOSED CURRENTRELEASE QA Contact: RHOS Documentation Team <rhos-docs>
Severity: high Docs Contact:
Priority: unspecified    
Version: 13.0 (Queens)CC: dalvarez, dcadzow, dsneddon, srevivo, vkommadi
Target Milestone: ---Keywords: Documentation, Triaged
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Hardware: Unspecified   
OS: Unspecified   
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Last Closed: 2019-04-05 13:36:01 UTC Type: Bug
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Bug Depends On: 1561880    
Bug Blocks:    

Description Daniel Alvarez Sanchez 2018-04-23 13:43:44 UTC 
Let's use this BZ to clearly document the limitations using OVN based deployments with VLAN tenant/provider networks.
Comment 2 anil venkata 2018-07-10 05:32:39 UTC 
When a VM spawned on VLAN network trying to reach external network(i.e SNAT), OVN(core ovn i.e ovn-controller) is redirecting this traffic from compute node to SNAT gateway node through tunnelling. As tunnelling overhead is added to the packet during redirect, this has to be considered when assigning MTU to VLAN network (during network creation).

But we can't hard code MTU (MTU - tunnel overhead i.e 1500 - 50)for vlan networks as this can impact  provider VLAN networks created on gateway node by admin user for external connectivity (which can't have this restriction as  traffic through this network is not redirected). 

This is a limitation in core OVN. Till this limitation is addressed in core OVN, we need to block tenants creating VLAN networks with OVN driver. Because of these reasons, OSP Director/Tripleo in OSP13 doesn't allow tenants to create VLAN networks.