IBM Support

Using External DHCP Server For Instances

Question & Answer


Question

Can instances on a compute node get IP addresses managed by an external DHCP server?

Answer

By using a nova-network, this can be accomplished. The following URL describes the different types of network configurations under a nova-network configuration :

http://docs.openstack.org/admin-guide-cloud/content/section_networking-options.html

A flat network manager configuration would accomplish the desired configuration. Here are the summary of steps :

1) Create a nova-network and specify a pool of IP addressses

2) An image to be deployed could be saved without any "cloud-init" activation and with a DCHP configured ethX interface

3) During the activation of the image, since there is no cloud-init, IP information from the nova-network would be ignored

4) Since the ethernet interface is configured for DCHP, the instance would try to broadcast to a DHCP server and if that DHCP server resides in the same subnet as the nova-network's subnet, it should be able to reach it and get a response back

Note: In this configuration, a nova list command would not show the assigned IP address from the external DHCP server.

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Document Information

Modified date:
17 June 2018

UID

nas8N1020831