[Openstack] Guest VM IP configuration script

Van Leeuwen, Robert rovanleeuwen at ebay.com
Fri Aug 26 20:07:25 UTC 2016

Are you sure it was DHCP misbehaving?
Because it could also have been that it tried to takeover the gateway IP.
That would certainly mess with connectivity on the network.

Just mentioning because you gave the example --router:external while I think it should be --router:external True

Also if it is dhcp misbehaving you might be able to fix it with the dnsmasq_config_file option in the dhcp agent. You can probably blacklist everything that does not start with the OpenStack MAC range. (Base_mac setting)

I currently don't have a setup to reproduce this so I cannot be 100% sure about the details or if this works ;-)

Robert van Leeuwen

> On 26 Aug 2016, at 18:58, Satish Patel <satish.txt at gmail.com> wrote:
> Robert,
> 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=
> network1
> 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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