[Bug 1722584] Re: [SRU] Return traffic from metadata service may get dropped by hypervisor due to wrong checksum

[Corey Bryant]

This is fixed in last week's eoan/train snapshot.

** Changed in: neutron (Ubuntu Eoan)
       Status: Triaged => Fix Released

** Changed in: cloud-archive/train
       Status: Triaged => Fix Released

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https://bugs.launchpad.net/bugs/1722584

Title:
  [SRU] Return traffic from metadata service may get dropped by
  hypervisor due to wrong checksum

Status in Ubuntu Cloud Archive:
  Triaged
Status in Ubuntu Cloud Archive queens series:
  Triaged
Status in Ubuntu Cloud Archive rocky series:
  Triaged
Status in Ubuntu Cloud Archive stein series:
  Triaged
Status in Ubuntu Cloud Archive train series:
  Fix Released
Status in neutron:
  Fix Released
Status in neutron package in Ubuntu:
  Fix Released
Status in neutron source package in Bionic:
  Triaged
Status in neutron source package in Cosmic:
  Triaged
Status in neutron source package in Disco:
  Triaged
Status in neutron source package in Eoan:
  Fix Released

Bug description:
  [Impact]
  Prior addition of code to add checksum rules was found to cause problems with newer kernels. Patch subsequently reverted so this request is to backport those patches to the ubuntu archives.

  [Test Case]
  * deploy openstack (>= queens)
  * create router/network/instance (dvr=false,l3ha=false)
  * go to router ns on neutron-gateway and check that the following returns nothing
  sudo ip netns exec qrouter-<id> iptables -t mangle -S| grep '\--sport 9697 -j CHECKSUM --checksum-fill'

  [Regression Potential]
  The original issue is no longer fixed once this patch is reverted.

  [Other Info]
  This revert patch does not remove rules added by the original patch so manual cleanup of those old rules is required.

  -----------------------------------------------------------------------------
  We have a problem with the metadata service not being responsive, when the proxied in the router namespace on some of our networking nodes after upgrading to Ocata (Running on CentOS 7.4, with the RDO packages).

  Instance routes traffic to 169.254.169.254 to it's default gateway.
  Default gateway is an OpenStack router in a namespace on a networking node.

  - Traffic gets sent from the guest,
  - to the router,
  - iptables routes it to the metadata proxy service,
  - response packet gets routed back, leaving the namespace
  - Hypervisor gets the packet in
  - Checksum of packet is wrong, and the packet gets dropped before putting it on the bridge

  Based on the following bug https://bugs.launchpad.net/openstack-
  ansible/+bug/1483603, we found that adding the following iptable rule
  in the router namespace made this work again: 'iptables -t mangle -I
  POSTROUTING -p tcp --sport 9697 -j CHECKSUM --checksum-fill'

  (NOTE: The rule from the 1st comment to the bug did solve access to
  the metadata service, but the lack of precision introduced other
  problems with the network)

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