Has anyone had an idea of what are the possible configuration design of a network infrastructure in an OpenStack environment to enable instances to have a public IP as a floating IP? An example below is a simple topology that I wish to accomplish, how would you integrate the public IP directly assign to instances in the topology? Thanks in advance.

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@Dohnal, thanks for the reply, and sorry for the lack of information in the original question and had to edit it but I really appreciate your answer.

  • What is the router model and configuration? We cannot help with configuration if we don't know what the device is. Please edit your question to provide the necessary information.
    – Ron Maupin
    Feb 25, 2018 at 4:13
  • Removed the off-topic request for resources.
    – Ron Maupin
    Feb 25, 2018 at 4:14
  • Hi Ron, sorry about that. Is it possible to change the question title and the body entirely, or would it be better to delete this and have a new one. Thanks
    – reynold
    Feb 26, 2018 at 4:35
  • That depends on if you want to preserve the answer (it would be bad form to orphan an answer that someone took the time to give you). A completely different question deserves a new question, but it is also possible to edit this one. When you edit a question that was placed on hold, it automatically comes up for a reopen vote.
    – Ron Maupin
    Feb 26, 2018 at 4:38
  • What is the router model and configuration? We need to know as much as possible.
    – Ron Maupin
    Feb 26, 2018 at 15:06

1 Answer 1


The problem is that a packet incoming on the local interface of the router/firewall with the public address e.g. cannot be routed by the router/firewall in NAT mode.

You have assigned the subnet to the public interface of the router and thus you cannot use the same subnet for internal network, which comes on another physical interface. Assigning the same subnet ( to two distinct physical interfaces of one router simply cannot work unless the router is set up as a bridge.

You do not have to define static NAT mappings for all the internal addresses, you can use NAT masquerade.

You can also use bridged mode as opposite to NAT mode on the router/firewall which allows you to have public IP adresses behing the firewall. See also this answer.

  • Hi Dohnal, thanks for the reply, I edited my post and sorry for lack of information
    – reynold
    Feb 25, 2018 at 4:10
  • @reynold I think that IPv4 public address should remain public and should be translated to local addresses, so your present configuration is OK. But in bridged mode it should be possible. Check this: serverfault.com/a/153418/229754 Feb 26, 2018 at 12:55
  • 1
    @Dohnal I search on bridge mode and I think this is a possible solution I am looking for. And now I am searching a way on how to integrate the bridge interfaces on the router in a leaf-spine topology up to the OpenStack hosts. Thank you so much.
    – reynold
    Feb 27, 2018 at 6:34

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