[Openstack] Guest VM IP configuration script

Satish Patel satish.txt at gmail.com
Fri Aug 26 16:58:25 UTC 2016


I remembered in JUNO release when i did flat network with my existing
provider LAN then DHCP started giving IPs to my existing LAN clients
and people started yelling their network is down :(

Following networking i configured.

 #neutron net-create network1 --provider:network_type flat
--provider:physical_network extnet  --router:external --shared

#neutron subnet-create --name subnet1 --enable_dhcp=True
--allocation-pool=start=,end= --gateway=

After realizing issue i have changed  --enable_dhcp=False

On Fri, Aug 26, 2016 at 2:35 AM, Van Leeuwen, Robert
<rovanleeuwen at ebay.com> wrote:
>> When i was trying to use DHCP in openstack i found openstack DHCP
>> start provide ip address to my existing LAN machines ( we are using
>> flat VLAN with neutron), that is why i disable openstack DHCP, Is it
>> common or i am doing something wrong?
> I do not think this should happen.
> It has been a while (Folsom) since I touched a setup with mixed “LAN” and OpenStack DHCP but IIRC it works like this:
> AFAIK the leases file neutron uses is very specific and will only reply to the mac-addresses that are in the dnsmasq config.
> Looking at the dnsmasq process it is set to static:
> From the 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.
> Usually the problem is the other way around:
> The existing DHCP in the “lan” bites with what OpenStack does. (so an OpenStack instance gets an IP from the lan DHCP)
> This can be prevented by blacklisting the MAC address range your instances get in your lan dhcp (Blacklist MAC starting with fa:16:3e )
> Cheers,
> Robert van Leeuwen

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