> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/ask/flat/chapter-24-advanced-networking/di-24.4-jie-vlan.md).

# 24.4 VLAN

A VLAN (Virtual Local Area Network) is a logical segment of a local area network (each segment has its own broadcast domain). A VLAN is isolated from other segments of the local area network, and computers on other segments can only access it through a connecting unit with filtering capabilities.

On FreeBSD, VLAN hardware offloading requires network card driver support; if the driver does not support it, VLAN tag processing will be handled by software, which may affect performance. To see which drivers support VLAN hardware offloading, refer to the [vlan(4)](https://man.freebsd.org/cgi/man.cgi?query=vlan\&sektion=4\&format=html) manual page.

When configuring a VLAN, the following information is needed: the network interface being used and the VLAN tag.

## Defining a VLAN

Assuming the network card is `em0` and the VLAN tag is `5`, the command is as follows:

```sh
# ifconfig em0.5 create vlan 5 vlandev em0 inet 192.168.20.20/24
```

> **Note**
>
> Note that the interface name includes the network card driver name and the VLAN tag, separated by a dot. This is the best practice, especially when multiple VLANs are configured on the machine, as it facilitates VLAN configuration management.

> **Note**
>
> When defining a VLAN, ensure that the parent network interface is also configured and enabled. In the example above, the simplest configuration is:
>
> ```sh
> # ifconfig em0 up
> ```

To configure the VLAN at boot time, **/etc/rc.conf** must be updated. To reproduce the above configuration, add the following:

```sh
vlans_em0="5"
ifconfig_em0_5="inet 192.168.20.20/24"
```

To add more VLANs, simply add the tag to the `vlans_em0` field and configure the network for the interface of that VLAN tag.

> **Note**
>
> When defining a VLAN in /etc/rc.conf, ensure that the parent network interface is also configured and enabled. In the example above, the simplest configuration is:
>
> ```sh
> ifconfig_em0="up"
> ```

## Assigning Symbolic Names to Interfaces

Assigning symbolic names to interfaces has practical value: when replacing associated hardware, only a few configuration variables need to be updated. For example, if a security camera needs to run VLAN 1 on `em0`, and the `em0` network card is later replaced with one using the ixgbe(4) driver, there is no need to change all references from `em0.1` to `ixgbe0.1`.

To configure VLAN `5` on network card `em0`, assign the interface name `cameras`, and allocate the IP address `192.168.20.20/24`, use the following command:

```sh
# ifconfig em0.5 create vlan 5 vlandev em0 name cameras inet 192.168.20.20/24
```

If the parent interface uses a different network card (for example, `video`, representing another physical network card in the system), use the following command:

```sh
# ifconfig video.5 create vlan 5 vlandev video name cameras inet 192.168.20.20/24
```

Add the following to **/etc/rc.conf** to apply the changes at boot time:

```sh
vlans_video="cameras"
create_args_cameras="vlan 5"
ifconfig_cameras="inet 192.168.20.20/24"
```


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