Incorrect MTU problem description

[Deepti Navale]

Jiri Benc from Red Hat raised a bug (RH bug: 1148011) against the Configuration Reference Guide, section http://docs.openstack.org/icehouse/config-reference/content/networking-options-plugins-ml2.html stating the following:

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MTU bug with VXLAN tunnelling

Due to a bug in Linux Bridge software maximum transmission unit (MTU) handling, using VXLAN tunnels does not work by default.
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This is incorrect and misleading. Bridging happens at layer 2 (Ethernet) and there's no concept of fragmentation at that layer. When a frame with a size exceeding target port MTU is to be transmitted, there's nothing the bridge can do other than dropping the frame. If an incoming frame is encapsulated into a tunnel header, its size is inevitably increased. If the frame was 1500 bytes long, it's over 1500 bytes after encapsulation.

I don't think there's a bug anywhere, this is just the behavior of networking (irritating behavior, granted). The documentation should be changed to not give the customers impression that there's a bug in our product that we're not fixing for some reason.

If you rather think this is indeed a bug in the Linux bridge, please explain how else should the bridge handle oversized frames.
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Raising this bug to fix this issue in the upstream Config reference guide.

[Tom Fifield (fifieldt)]

The discussion that led to this note can be found at https://bugs.launchpad.net/openstack-manuals/+bug/1242534 - any change should ensure that the original reports intent to help users in this case is preserved.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/131325

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/131325
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=ec5328e92ed8ab31c57982de51b8fac322a54ed0
Submitter: Jenkins
Branch: master

commit ec5328e92ed8ab31c57982de51b8fac322a54ed0
Author: Deepti Navale <email address hidden>
Date: Tue Oct 28 12:22:19 2014 +1100

    Improve wording in section Modular Layer 2 configuration options

    Minor updates to terminology around VXLAN MTU configuration.
    Closes-Bug: #1383958

    Change-Id: If885dd795a4af35c1fee755238b3c3482a17cd9f

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/openstack-manuals 15.0.0 release.