Configure network node in OpenStack Installation Guide for Ubuntu 12.04/14.04 (LTS) - icehouse - MTU size

[Marco CONSONNI]

This is a subtle and annoying bug explained here (https://ask.openstack.org/en/question/7156/text-editors-vim-nano-emacs-freezes-my-ssh-session-in-ubuntu-instances-1310-1304-and-12042-server/) and reported as an anecdote here (http://docs.openstack.org/openstack-ops/content/double_vlan.html) .
It is related to MTU size.

I followed the instructions in this guide and quite smoothly I configured a three node OpenStack deployment. Then, I launched a cirros image, associated a floating IP address and ping/ssh. Fine!
Afterwards, I loaded an Ubuntu image taken from the official repository, I launched, associated an IP address, ping but I was not able to SSH.
After some troubles reported here https://ask.openstack.org/en/question/33625/ubuntu-instances-refuse-ssh/ (see my comments tagged as "MCo"), I found out where the problem was and how to fix it.

The problem is that MTU packets are dropped sometimes and this prevent any sensible usage of virtual machines running in the cloud.
In order to fix the problem, you need to

1) create file /etc/neutron/dnsmasq-neutron.conf and write

         dhcp-option-force=26,1454

2) edit /etc/neutron/dhcp_agent.ini and under [DEFAULT] section, add:

   dnsmasq_config_file = /etc/neutron/dnsmasq-neutron.conf

This fixes the problem because it forces the instances to send MTUs with a size that can be digested by OpenvSwitch configured for GRE tunneling.

I recommend to add these configuration steps above in the "Configure network node" section.

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Built: 2014-07-22T20:08:37 00:00
git SHA: d8d5739b67867a56e7ec64e35bd15eef06e1b3c5
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)]

Thanks for the additional information!