Bug 1955029 - [ovn][migration][docs] MTU considerations during migration
Summary: [ovn][migration][docs] MTU considerations during migration
Keywords:
Status: ON_DEV
Alias: None
Product: Red Hat OpenStack
Classification: Red Hat
Component: documentation
Version: 16.1 (Train)
Hardware: Unspecified
OS: Unspecified
high
unspecified
Target Milestone: z4
: 16.2 (Train on RHEL 8.4)
Assignee: James Smith
QA Contact: Roman Safronov
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2021-04-29 09:51 UTC by Daniel Alvarez Sanchez
Modified: 2023-08-03 15:44 UTC (History)
5 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
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Target Upstream Version:
Embargoed:
jamsmith: needinfo? (dalvarez)
mtomaska: needinfo-

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Red Hat Issue Tracker OSP-3473 0 None None None 2021-12-22 20:07:29 UTC

Description Daniel Alvarez Sanchez 2021-04-29 09:51:32 UTC 
The current migration process assumes moving to Geneve overlay which implies an adjustment of the workloads MTU before the actual migration happens (default MTU for VXLAN is 1450 while default MTU for Geneve is 1442).

Adjusting the MTU is not going to be always possible since it may depend on the actual guest DHCP client, and sometimes the instances won't even have DHCP enabled and may require a hard reboot.

The doc should capture this and warn the user so that, whenever possible, the MTU is left untouched (eg. 1450) if the underlying physical networks would be on Jumbo frames (or an MTU larger than 1508 bytes). This would save the MTU adjustment step and reduce risks.
Comment 2 James Smith 2021-05-04 13:07:38 UTC 
SME Daniel
Affects 16.1 and later
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