HP-UX VLAN Administrator's Guide, February 2007

Configuring VLANs on the Switch
IEEE 802.1Q-compliant devices can coexist with legacy and untagged VLANs on the same
networks. However, legacy and untagged VLANs require a separate link, whereas the
802.1Q-tagged VLANs can combine several VLANs into one link (see Figure 1-6). On
802.1Q-compliant devices, separate ports (configured as untagged) must be used to connect
separate VLANs to non-802.1Q devices.
Figure 1-6 Tagged and Untagged VLAN Technology in the Same Network
VLAN 1 Untagged or Native VLAN
VLAN 2 Tagged VLAN
VLAN 3 Tagged VLAN
VLAN 4 Tagged VLAN
Untagged
LAN
Card
Port
Tagged
Switch Port
When you assign a switch port to a given VLAN, you must implement the VLAN tag if the switch
port carries traffic for more than one VLAN. Otherwise, the port VLAN assignment can remain
untagged because the tag is not needed. On a given switch, use the untagged designation for a
port VLAN assignment when the port is connected to a non-802.1Q-compliant device or is
assigned to only one VLAN, as shown by VLAN 1 in Figure 1-6. Use the tagged designation
when more than one VLAN is assigned to the port, or when the port is connected to a device
that does comply with the 802.1Q standard, as shown by VLAN 2, VLAN 3, and VLAN 4 in
Figure 1-6.
These rules are summarized in Table 1-1.
Table 1-1 Summary of VLAN Tagging Assignment
Tagging SchemeVLANs per Port
Untagged or tagged. If the device connected to the port is 802.1Q-compliant, then the
recommended choice is tagged.
1
1 VLAN untagged; and all others tagged
or all VLANs tagged.
2 or more
A given VLAN must have the same VLAN ID on any 802.1Q-compliant device on which the
VLAN is configured.
VLANs on HP-UX
HP-UX implements VLAN tagging using VLAN interfaces. At the time it is configured, a VLAN
interface is assigned a VLAN ID that identifies the VLAN it is part of. The VLAN ID is unique
on the physical interface on which the VLAN interface is created. VLAN interfaces that share
the same VLAN ID can communicate to each other as if they were on the same physical network.
On each NIC port, you can configure multiple VLAN interfaces, each of which is associated with
a unique VLAN ID and 802.1p priority value. Each VLAN interface is assigned a virtual PPA
(VPPA), which you can then use just like any other PPA – to configure protocols, attach to
applications, and so on .
20 Introduction