[openstack-dev] [Neutron][Nova][DHCP] Use case of enable_dhcp option when creating a network

Padmanabhan Krishnan kprad1 at yahoo.com
Wed Dec 17 17:04:24 UTC 2014

Thanks for the response, i saw the other thread in the morning. Will use that thread, if i have further questions.

From: Pasquale Porreca <pasquale.porreca at dektech.com.au>
Reply-To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org>
Date: Wednesday, December 17, 2014 12:37 AM
To: "openstack-dev at lists.openstack.org" <openstack-dev at lists.openstack.org>
Subject: Re: [openstack-dev] [Neutron][Nova][DHCP] Use case of enable_dhcp option when creating a network

Just yesterday I asked a similar question on ML, this is the answer I got:

In Neutron IP address management and distribution are separated concepts.IP addresses are assigned to ports even when DHCP is disabled. That IP address is indeed used to configure anti-spoofing rules and security groups.

On 12/17/14 09:15, Padmanabhan Krishnan wrote:

Hello,I have a question regarding the enable_dhcp option when creating a network.

When a VM is attached to  a network where enable_dhcp is False, I understand that the DHCP namespace is not created for the network and the VM does not get any IP address after it boots up and sends a DHCP Discover.But, I also see that the Neutron port is filled with the fixed IP value from the network pool even though there's no DHCP associated with the subnet. So, for such VM's, does one need to statically configure the IP address with whatever Neutron has allocated from the pool?
What exactly is the use case of the above? 
I do understand that for providing public network access to VM's, an external network is generally created with enable-dhcp option set to False. Is it only for this purpose?
I was thinking of a case of external/provider DHCP servers from where VM's can get their IP addresses and when one does not want to use L3 agent/DVR. In such cases, one may want to disable DHCP when creating networks.  Isn't this a use-case?
Appreciate any response or corrections with my above understanding.


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Pasquale Porreca

DEK Technologies
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