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[Bug 1888666] [NEW] Disabling/enabling networks in neutron causes traffic loop with linxbridge agent

To: yahoo-eng-team@xxxxxxxxxxxxxxxxxxx
From: Sebastian Lohff <1888666@xxxxxxxxxxxxxxxxxx>
Date: Thu, 23 Jul 2020 13:03:53 -0000
Reply-to: Bug 1888666 <1888666@xxxxxxxxxxxxxxxxxx>
Sender: bounces@xxxxxxxxxxxxx

Public bug reported:

We observed traffic looping between two linuxbridge agents after a user
disabled and then reenabled the network. Disabling a network causes all
vethX interfaces to be cleaned from the bridge, but the physical
interface remains in the bridge. Disabling the network will also cause a
segment release for the segment the network agent is on in a
hierarchical port binding setup. When reenabling the network a new VLAN
id might be generated for the segment the network agent is on and thus
the physical interface will be added with the new VLAN id. With two
network agents bridging two different VLANs we get a loop.

Quick mitigation would be to identify the bridge with two physical
interfaces in it, identify the stale interface and remove it.

Tested with Neutron Queens. Network was disabled/enabled via openstack
network set --disable/--enable $uuid

** Affects: neutron
     Importance: Undecided
         Status: New


** Tags: linuxbridge

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https://bugs.launchpad.net/bugs/1888666

Title:
  Disabling/enabling networks in neutron causes traffic loop with
  linxbridge agent

Status in neutron:
  New

Bug description:
  We observed traffic looping between two linuxbridge agents after a
  user disabled and then reenabled the network. Disabling a network
  causes all vethX interfaces to be cleaned from the bridge, but the
  physical interface remains in the bridge. Disabling the network will
  also cause a segment release for the segment the network agent is on
  in a hierarchical port binding setup. When reenabling the network a
  new VLAN id might be generated for the segment the network agent is on
  and thus the physical interface will be added with the new VLAN id.
  With two network agents bridging two different VLANs we get a loop.

  Quick mitigation would be to identify the bridge with two physical
  interfaces in it, identify the stale interface and remove it.

  Tested with Neutron Queens. Network was disabled/enabled via openstack
  network set --disable/--enable $uuid

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