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[OpenStack Infra <1495444@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.openstack.org/244722
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=47713f58701af9e27792230dd64daa3e20a4260b
Submitter: Jenkins
Branch:    master

commit 47713f58701af9e27792230dd64daa3e20a4260b
Author: sridhargaddam <sridhar.gaddam@xxxxxxxxxxxx>
Date:   Thu Nov 12 15:49:15 2015 +0000

    Support MTU advertisement using IPv6 RAs
    
    RFC4861 allows us to specify the Link MTU using IPv6 RAs.
    When advertise_mtu is set in the config, this patch supports
    advertising the LinkMTU using Router Advertisements.
    
    Partially Implements: blueprint mtu-selection-and-advertisement
    Closes-Bug: #1495444
    Change-Id: I50d40cd3b8eabf1899461a80e729d5bd1e727f28


** Changed in: neutron
       Status: In Progress => Fix Released

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https://bugs.launchpad.net/bugs/1495444

Title:
  MTU Option should be included in ICMPv6 Router Advertisements

Status in neutron:
  Fix Released

Bug description:
  When using an overlay network on a physical network with standard
  Ethernet MTU (1500 octets), the instances' effective MTU is reduced.

  The Neutron Router should inform the nodes about this fact, by
  including the MTU Option in the ICMPv6 Router Advertisements it sends.
  The current situation leads to blackholing of traffic, as the absence
  of the MTU Option causes the instance to believe it will be able to
  successfully transmit 1500 octets large frames to the network.
  However, these will be silently discarded. The symptom of is usually
  that the TCP three-way handshake succeeds, but that the connection
  appears to hang the moment payload starts being transmitted.

  The MTU Option is documented here:
  https://tools.ietf.org/html/rfc4861#section-4.6.4. The corresponding
  radvd.conf option is called AdvLinkMTU. Note that the Neutron router
  is clearly aware of the reduced effective MTU, as it does use the
  corresponding DHCPv4 option to advertise it to instances/subnets using
  IPv4.

  I observe this problem on OpenStack Kilo.

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