[Openstack] Guest VM IP configuration script

Van Leeuwen, Robert rovanleeuwen at ebay.com
Wed Aug 31 06:15:06 UTC 2016

On 8/30/16, 4:44 PM, "Satish Patel" <satish.txt at gmail.com> wrote:

>    Robert,
>    I didn't find any related configuration which blacklist mac address on
>    Mitaka. also i didn't find any document stated that DHCP agent only
>   gives ip address to instance mac address.

I am not sure if there is any specific doc about this on the OpenStack pages.
However, neutron starts a dnsmasq process so you can have a look with ps on how that is running and configured.

I am no dnsmasq expert but I looking at the dnsmasq man page:
“The optional <mode> keyword may be static which tells dnsmasq to enable DHCP for the network specified, but not to dynamically allocate IP addresses: only hosts which have static addresses given via dhcp-host or from /etc/ethers will be served”

When you look at the dnsmasq process on a neutron server it is indeed set to static and uses the –dhcp-host options:
dnsmasq  --dhcp-range=set:tag0,,static,5529600s  --dhcp-hostsfile=/var/lib/neutron/dhcp/123-4567/host --lots_of_other_options

Last time I had this scenario it was 2 years ago so my memory could be deceiving me but this was also the behavior I experienced.
(Not 100% sure but I think we did have a custom build dnsmasq because the centos 6 version did not support all the required options or something.
Since it was at a previous job I can no longer check but I am pretty sure it worked with 2 dhcp servers in the same range. 
Although it also depends a bit on which DHCP responds quicker on what behavior you will see exactly. In theory our “LAN” dhcp just could have been consistently quicker)

Robert van Leeuwen

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