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Bug 1766683

Summary: [Docs] Document that updating a MTU of a network requires restarting the VM
Product: Red Hat Enterprise Virtualization Manager Reporter: Dominik Holler <dholler>
Component: DocumentationAssignee: rhev-docs <rhev-docs>
Status: CLOSED CURRENTRELEASE QA Contact: Michael Burman <mburman>
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: cminkema, gveitmic, lleistne, lsurette, mburman, michael.burman, mkalinin, rdlugyhe, srevivo
Target Milestone: ovirt-4.4.1Keywords: Documentation
Target Release: 4.4.1Flags: rdlugyhe: needinfo-
lsvaty: testing_plan_complete-
Hardware: Unspecified   
OS: Unspecified   
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Fixed In Version: Doc Type: If docs needed, set a value
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Last Closed: 2020-06-09 12:30:04 UTC Type: Bug
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Verified Versions: Category: ---
oVirt Team: Network RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
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Description Dominik Holler 2019-10-29 16:28:42 UTC 
Description of problem:
In https://bugzilla.redhat.com/show_bug.cgi?id=1766414#c4 was raised that a hint  in the docs that updating the MTU might trigger issues for a running VM connected to the related network.

Adding something like
'The MTU is applied during the start of the VM or hot plugging the network interface, but not during an update of the network. Therefore, the vNICs of running VMs have to be hot unplugged and hot re-plugged to apply the MTU update.' to Table 6.1. New Logical Network and Edit Logical Network Settings
in the Admin guide would be helpful.

Version-Release number of selected component (if applicable):
All RHV versions up to 4.4 .
Comment 5 Rolfe Dlugy-Hegwer 2020-06-04 16:50:45 UTC 
The updated documentation contains notes stating:

IMPORTANT
If you change the network’s MTU settings, you must propagate this change to the running virtual machines on the network: Hot unplug and replug every virtual machine’s vNIC that should apply the MTU setting, or restart the virtual machines. Otherwise, these interfaces fail when the virtual machine migrates to another host. For more information, see BZ#1766414.

See:
- https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.4-beta/html-single/administration_guide/index
- https://access.redhat.com/documentation/en-us/red_hat_virtualization/4.4-beta/html-single/planning_and_prerequisites_guide/index