Virtual Local Area Networks

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VLANs (Virtual Local Area Networks) can be thought of as logical broadcast domains. A VLAN splits up groups of network users on a real physical network onto segments of logical networks.

This implementation supports the IEEE 802.1Q VLAN tagging standard with the capability to support multiple VLAN IDs running on Ethernet adapters. Each VLAN ID is associated with a separate Ethernet interface to the upper layers (IP, etc.) and creates unique logical Ethernet adapter instances per VLAN, for example ent1, ent2 and so on.

The IEEE 802.1Q VLAN support can be configured over any supported Ethernet adapters. The adapters must be connected to a switch that supports IEEE 802.1Q VLAN.

You can configure multiple VLAN logical devices on a single system. Each VLAN logical devices constitutes an additional Ethernet adapter instance. These logical devices can be used to configure the same Ethernet IP interfaces as are used with physical Ethernet adapters. As such, the no option, ifsize (default 8), needs to be increased to include not only the Ethernet interfaces for each adapter, but also any VLAN logical devices that are configured. See the no command documentation.

Each VLAN can have a different maximum transmission unit (MTU) value even if sharing a single physical Ethernet adapter.

VLAN support is managed through SMIT. Type the smit vlan fast path from the command line and make your selection from the main VLAN menu. Online help is available.

After you configure VLAN, configure the IP interface, for example, en1 for standard Ethernet or et1 for IEEE 802.3, using SMIT, or commands.

AIX® 5.3 and later supports virtual Ethernet using a virtual I/O switch as a method to perform in-memory communication between partitions in a POWER5 system. The switch also supports IEEE 802.1Q tagging, which allows the virtual Ethernet adapters to belong different VLANs on the switch. Virtual Ethernet adapters are created and configured on partitions using the Hardware Management Console (HMC). After it is created, the partition will see the virtual Ethernet adapter in the open firmware tree when it scans for devices. After it is detected, the virtual Ethernet adapter is configured and used just like a physical Ethernet adapter. For more information, see the hardware documentation for your POWER5 system.

Note:

If you try to configure a VLAN ID value that is already in use for the specified adapter, the configuration fails with the following error:

Method error (/usr/lib/methods/chgvlan):
  0514-018 The values specified for the following attributes
           are not valid:
           vlan_tag_id    VLAN Tag ID

If a user (for example, IP interface) is currently using the VLAN logical device, any attempt to remove the VLAN logical device fails. A message similar to the following displays:
```
Method error (/usr/lib/methods/ucfgcommo):
        0514-062 Cannot perform the requested function because the
                 specified device is busy.
```
To remove the logical VLAN device, first detach the user. For example, if the user is IP interface en1, then you can use the following command:
```
ifconfig en1 detach
```
Then remove the network interface using the SMIT TCP/IP menus.
If a user (for example, IP interface) is currently using the VLAN logical device, any attempt to change the VLAN characteristic (VLAN tag ID or base adapter) fails. A message similar to the following displays:
```
Method error (/usr/lib/methods/chgvlan):
        0514-062 Cannot perform the requested function because the
                 specified device is busy.
```
To change the logical VLAN device, first detach the user. For example, if the user is the IP interface en1, you could use the following command:
```
ifconfig en1 detach
```
Then change the VLAN and add the network interface again using the SMIT TCP/IP menus.