unable to use/assign specific fixed IP - reserved_dhcp_port.

Brian Haley haleyb.dev at gmail.com
Mon Dec 14 20:54:40 UTC 2020

On 12/14/20 1:02 PM, lejeczek wrote:
> Hi guys.
> I'm try to spin up and instance:
> $ openstack server create midway --flavor C1.vss.tiny --volume midway 
> --nic net-id=fd8659cf-8723-4254-bf88-837b37a50a24,v4-fixed-ip=
> Fixed IP address is already in use on instance 
> reserved_dhcp_port. (HTTP 400) (Request-ID: 
> req-bf34b06c-d0b7-4798-8eeb-9f5bb87348e2)
> Having no admin access to the stack - how to troubleshoot and ideally 
> resolve it before I have to admins demanding action :)
> many thanks, L.

When the device ID is set to "reserved_dhcp_port" someone has done it 
manually, so you might be out of luck if you don't have admin rights to 
the subnet.  And if there are already instances booted on it the DHCP IP 
change could cause some connectivity issues (e.g. DNS).

On a related note, if you can create your own subnet, the best way to 
make sure an IP is not assigned is by specifying the allocation pool 
when you create it, for example:

$ openstack subnet create --network private --subnet-range 
--allocation-pool start=,end= --gateway 

That way it shouldn't allocate to an instance.  Without looking 
into the code further I can't remember if the DHCP port has to follow 
the allocation pool restrictions though.


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