--- title: "Managing public IPs" description: "Find out how to assign, move and release public IP addresses on SNC Cloud Platform using independent Neutron ports that survive instance recreation" url: https://docs.ovhcloud.com/de/guides/hosted-private-cloud/cloud-platform/public-ip-management lang: de lastUpdated: 2026-09-29 --- > For AI agents: the complete documentation index is available at https://docs.ovhcloud.com/de/llms.txt, the full documentation bundle is available at https://docs.ovhcloud.com/de/llms-full.txt. # Managing public IPs ## Objective Practical guide to assigning, moving, and releasing public IP addresses on this platform via independent Neutron ports. The additional-IP feature is landing with major release #2; in the meantime, keeping the same public address across instances calls for dedicated management, detailed here. Target audience: anyone provisioning instances on this platform. This guide describes how to manage public IP addresses on this platform so they can be **detached from one instance and reattached to another** without being lost — a common need (instance recreation, migration, switching a test environment) that, without care, results in the IP disappearing. ## Overview The additional-IP feature will be available starting with the platform's major release #2. In the meantime, a public IP is obtained by attaching a **second network interface directly to the shared external network `Ext-Net`** — which calls for dedicated management to keep the same address across instances. The approach to favour is creating the Neutron port **independently** of any instance, then attaching it to instance A. You can then detach that independent port from instance A and attach it to instance B without losing the address. This guide details how to implement this approach, including one limitation to be aware of (see the note in [step 1](#step-1--creating-an-independent-port-on-ext-net)). ## Requirements - The `openstack` CLI configured (see the [Terraform guide](https://docs.ovhcloud.com/de/guides/hosted-private-cloud/cloud-platform/terraform.md) for `clouds.yaml`-based authentication). - The ID of the `Ext-Net` external network and its subnet: ```bash openstack network show Ext-Net -f value -c id openstack subnet list --network Ext-Net -f value -c ID ``` ## Instructions ### Independent port vs. implicit port Whether a Neutron port survives an instance's lifecycle depends **entirely on how it was created**, not on its attachment state at any given moment: | | **Implicit** port | **Independent** port | | ---------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------- | | Creation | `openstack server create --nic net-id=` — Nova creates the port itself | `openstack port create --network ` — created separately, **before** any instance | | Attachment | `--nic net-id=` at instance creation | `--nic port-id=` at creation, or `openstack server add port` afterwards | | Instance deletion | The port is **automatically deleted** along with the instance — the IP goes back to the pool | The port **survives** instance deletion | | Live detach (`server remove port`) | The port is **deleted immediately**, not just detached (empirically verified behaviour, see [known pitfalls](#known-pitfalls-troubleshooting)) | The port stays detached, reattachable at will | **Practical consequence: always create the port separately, before the instance, whenever you want to keep the option of reusing the IP.** There is no way to "convert" an already-attached implicit port into an independent one afterwards. Attempting it (detach then reattach) destroys the port and releases the IP back to the pool, just like any deletion. ### Step 1 — Creating an independent port on `Ext-Net` ```bash EXTNET_ID=$(openstack network show Ext-Net -f value -c id) openstack port create --network $EXTNET_ID --security-group my-public-port ``` Neutron automatically assigns a free IP from the `Ext-Net` pool. Retrieve the address: ```bash openstack port show my-public-port -f value -c fixed_ips ``` :::info **Good to know**: on `Ext-Net`, the address is always auto-assigned from the pool — picking a specific IP ahead of time is not possible: ```bash openstack port create --network $EXTNET_ID \ --fixed-ip subnet=,ip-address=192.0.2.10 my-public-port # ForbiddenException: 403 ... rule:create_port:fixed_ips:ip_address ... disallowed by policy ``` The benefit of an independent port remains fully intact (portability across instances); only the ability to **pick** the address ahead of time is missing. On a private network (e.g. an internal network you created), choosing a specific IP works normally. ::: ### Step 2 — Attaching the port to a new instance ```bash openstack server create \ --flavor \ --nic net-id= `# private interface, implicit: fine, no public IP to lose` \ --nic port-id=my-public-port `# public interface, ALWAYS via port-id` \ --image \ my-instance ``` ### Step 3 — Attaching the port to an already-existing instance If the instance was created before the port, or already exists without a public interface: ```bash openstack server add port my-instance my-public-port ``` Verify: ```bash openstack server show my-instance -f value -c addresses ``` ### Step 4 — Moving the IP to another instance This is the target scenario of this guide: reusing the same public IP after recreating or replacing an instance. ```bash # detach from instance A openstack server remove port instance-a my-public-port # reattach to instance B openstack server add port instance-b my-public-port ``` The port — and therefore the IP — is never returned to the pool: it moves directly from one instance to the other. Expect a few seconds of network interruption during the detach/attach. :::warning This operation is only safe **on a port created independently** ([step 1](#step-1--creating-an-independent-port-on-ext-net)). On an implicit port, `server remove port` destroys it immediately instead of detaching it — see [known pitfalls](#known-pitfalls-troubleshooting). ::: ### Step 5 — Finding which IP is attached to which instance ```bash # all IPs across all instances openstack server list -f table -c Name -c Networks # port-level detail (ID, fixed IP, owning instance) openstack port list -f table -c ID -c "Fixed IP Addresses" -c "Device ID" # find the port for a specific IP openstack port list -f value -c ID -c "Fixed IP Addresses" | grep 192.0.2.10 ``` A port with an empty `Device ID` column is **detached** (independent and currently free, ready to be attached to an instance). ### Step 6 — Releasing a port If the IP is no longer needed, deleting the port returns it to the `Ext-Net` pool: ```bash # detach first if still attached openstack server remove port openstack port delete ``` ### Known pitfalls (troubleshooting) | Symptom | Cause | Fix | | ------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | The public IP changes after deleting/recreating an instance | The port carrying the IP was **implicit** (`--nic net-id=` at creation), so it was automatically deleted along with the instance | Always create the port separately ([step 1](#step-1--creating-an-independent-port-on-ext-net)) before creating any instance you may later recreate | | `openstack server remove port` makes the port disappear instead of detaching it (`openstack port show` returns `No Port found`) | Attempting to detach an **implicit** port — Nova deletes it immediately rather than freeing it, whether via instance deletion or manual detach | Create a new independent port ([step 1](#step-1--creating-an-independent-port-on-ext-net)) and attach it — the old IP is lost, a new one is assigned from the pool | | `403 Forbidden` on `openstack port create --fixed-ip ip-address=...` on `Ext-Net` | Picking a specific public IP is not available on this platform | Accept the auto-assigned IP from the pool; the portability benefit of the independent port remains fully intact | | The instance gets no public IP after `server add port` | Port's security group too restrictive, or port on the wrong network | Check the security group attached to the port (`openstack port show -c security_group_ids`) and the target network (`openstack port show -c network_id`) | | IP needs reconfiguring inside the OS after a public IP change | The VM has no cloud-init (Windows VM), so nothing re-reads the IP from metadata at boot — on a Linux VM with cloud-init, this is generally not needed | Reconfigure the IP manually inside the OS after any port change — see the [Creating a Windows Server VM](https://docs.ovhcloud.com/de/guides/hosted-private-cloud/cloud-platform/create-windows-server-vm.md) guide | ## Go further [Terraform guide](https://docs.ovhcloud.com/de/guides/hosted-private-cloud/cloud-platform/terraform.md) — network attachment pattern (second interface on `Ext-Net`), section "No floating IP / Neutron router". [Creating a Windows Server VM](https://docs.ovhcloud.com/de/guides/hosted-private-cloud/cloud-platform/create-windows-server-vm.md) — manual IP configuration after a change, on a Windows VM. Official OpenStack CLI documentation on ports: [docs.openstack.org — Network v2](https://docs.openstack.org/python-openstackclient/latest/cli/command-objects/network/v2/index.html#port). For training or technical assistance implementing our solutions, contact your sales representative or visit our [Professional Services](https://www.ovhcloud.com/de/professional-services/) page to request a quote and have your project analysed by our experts. Join our [community of users](https://community.ovhcloud.com/).