> For the complete documentation index, see [llms.txt](https://docs.up-network.ch/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.up-network.ch/documentation/guides/how-to-use-additional-ipv4-addresses-on-a-dedicated-server.md).

# How to Use Additional IPv4 Addresses on a Dedicated Server

**Overview**

On our network, **only one MAC address is authorized per physical network port**.\
This means that all traffic must originate from the server’s main network interface.

To prevent IP conflicts, MAC spoofing, and network disruptions, additional IPv4 addresses must be configured using **routing via the main server IP**, not directly on the switch.

This ensures that the server itself handles the traffic forwarding.

***

### Network Policy

* ✅ Only **one MAC address** is allowed per physical port
* ❌ No additional MAC addresses (VPS, VM, containers) are permitted on the switch
* ✅ All extra IPv4 addresses must be **routed through the main server IP**
* ✅ The dedicated server acts as a **gateway** for its additional IPs

This design improves network stability and security.

***

### Example Scenario

Main server IP:

```
10.10.10.55
```

Additional IPv4 addresses:

```
10.10.10.56
10.10.10.57
```

Default gateway of the network:

```
10.10.10.1
```

#### ⚠️ Important

**Do NOT use 10.10.10.1 as the gateway for additional IPs.**

Instead, use the main server IP as the gateway.

***

### Correct Configuration

#### Additional IP Configuration

Each additional IP must use the **main server IP as its gateway**.

Example:

```
IP Address:   10.10.10.56/XX
Gateway:      10.10.10.55
```

```
IP Address:   10.10.10.57/XX
Gateway:      10.10.10.55
```

Where:

* `XX` = subnet mask (provided by us)
* `10.10.10.55` = main server IP

***

### Why This Is Required

Because only one MAC address is allowed:

* The switch only sees the main server
* All traffic must pass through the server
* The server routes packets internally

This prevents:

* MAC spoofing
* Unauthorized IP usage
* Network instability
* Service interruptions

***

### Server Role

Your dedicated server acts as:

* A **router**
* A **gateway**
* A **traffic forwarder**

All additional IP traffic goes through the main interface.

This applies to:

* Virtual machines
* Containers
* VPS
* Custom network setups

***

### Typical Use Cases

This configuration is required when using:

* VMware / Proxmox / KVM
* Docker / LXC
* Virtual firewalls
* Internal sub-networks

Example:

```
VM → Main Server → Switch → Internet
```

The VM never communicates directly with the switch.

***

### Common Mistakes

#### ❌ Wrong Configuration

Using the network gateway directly:

```
Gateway: 10.10.10.1
```

This may cause:

* Packet loss
* IP blocking
* Network shutdown
* Port security violations

#### ✅ Correct Configuration

```
Gateway: Main Server IP
```

***

### Advanced Routing (Optional)

On the main server, IP forwarding must be enabled:

#### Linux

```
sysctl -w net.ipv4.ip_forward=1
```

Persistent:

```
net.ipv4.ip_forward = 1
```

in `/etc/sysctl.conf`

You may also need NAT or static routes depending on your setup.

***

### Security Notice

Our infrastructure enforces:

* MAC address filtering
* Anti-spoofing rules
* Port security
* Traffic monitoring

Any non-compliant configuration may result in automatic blocking.

***

### Support & Managed Services

If you are unsure about the configuration, or if you need assistance with:

* Routing
* Virtualization
* Firewall setup
* Network optimization

Our managed services team can provide full support and maintenance.

Please contact us for more information.