MTU should be Configured in network node in OpenStack Installation Guide for Ubuntu 12.04/14.04 (LTS) - icehouse

[hegaofeng]

this is a suggestion
GRE tunnel is used in this install guide, so MTU is no longer 1500(Ethernet default value both in Linux & Windows) for virtual machines inside the OpenStack. although after launched two VMs, ping (default payload length, >1454? will fail) between them and the other physical nodes seem normal, ssh connection & wget is always failed (stuck & awaiting).

i searched the doc of previous openstack release, found it points out the MTU should be set in the dnsmasq dhcp configuration file(dhcp-option-force=26,1400). 1400 is still not a suitable value. i can't download any files when i try to use vpn in the VM, thought the connection was established. it says common default MTU value for vpn is 1400, so after the protocol headers combined with the data payload, the packet size exceeds the virtual Ethernet MTU set as 1400. in my environment 1500(physical Ethernet MTU) - 20(IP header) - 8(GRE header) - 18(wrapped virtual Ethernet frame header) = 1454 works well

this problem puzzled me a few days

refer links:
https://ask.openstack.org/en/question/6140/quantum-neutron-gre-slow-performance/
http://techbackground.blogspot.com/2013/06/path-mtu-discovery-and-gre.html
http://packetlife.net/blog/2008/aug/18/path-mtu-discovery/
http://openstack.redhat.com/forum/discussion/302/quantumneutron-and-ip-packet-mtus-questions-answers-and-suggestions/p1

-----------------------------------
Built: 2014-05-16T14:22:56 00:00
git SHA: ed92ea154f460d78c24ec7323da3a649591a801a
URL: http://docs.openstack.org/icehouse/install-guide/install/apt/content/neutron-ml2-network-node.html
source File: file:/home/jenkins/workspace/openstack-manuals-tox-doc-publishdocs/doc/install-guide/section_neutron-ml2-network-node.xml
xml:id: neutron-ml2-network-node

[Gauvain Pocentek (gpocentek)]

I hit a problem of the same kind today, although I'm not entirely sure it is the same. I'll do a fresh installation following the guide ASAP to validate this behavior.

thanks for the report!

[Tom Fifield (fifieldt)]

Thanks for the report indeed!

Setting to incomplete during GP's investigation

[Gauvain Pocentek (gpocentek)]

https://bugs.launchpad.net/openstack-manuals/+bug/1348165 has extra information about the dhcp agent setup.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/114802

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/114802
Committed: https://git.openstack.org/cgit/openstack/openstack-manuals/commit/?id=951c047c28fe5b2670e5d3364d00ce30d120ab62
Submitter: Jenkins
Branch: master

commit 951c047c28fe5b2670e5d3364d00ce30d120ab62
Author: Matthew Kassawara <email address hidden>
Date: Sun Aug 17 02:28:15 2014 +0000

    Update neutron network node section to adjust MTU

    I updated the neutron network node section to discuss the
    implications of tunneling protocols such as GRE, provide
    potential solutions, and recommend using DHCP to adjust the
    instance MTU.

    This patch does not address the equivalent section for the
    deprecated OVS plug-in.

    Change-Id: Ia8dd9fe78d5c845c85bfde0d96481a55f754e121
    Closes-Bug: #1322799

[OpenStack Infra (hudson-openstack)]

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