Planning and Implementing VLANs with HP-UX

suits your needs, you must understand what each type of usage scenario implies. On HP-UX,
the type of VLAN configured on a NIC port depends on how you configure virtual interfaces
and use them.
• Port-based VLAN: All frames transmitted by a NIC are tagged using only one VLAN ID.
The NIC does not transmit or receive any untagged frames.
To implement this on HP-UX, you create just one VI on a given NIC port. All protocols and
applications use this virtual interface’s virtual PPA to transmit data traffic. Therefore all
frames transmitted by that NIC port are tagged with the VLAN ID of that VI.
• Protocol-based VLAN: The NIC assigns a unique VLAN ID for each Layer 3 protocol (such
as IPv4, IPv6, IPX, and so on). Therefore, the VLAN ID of outbound frames is different for
each protocol. An inbound frame is dropped if the protocol and VLAN ID do not match.
To implement this on HP-UX, you create one VI per Layer 3 protocol processed by the NIC.
You then configure the protocol (for example, ifconfig) using the VPPA of each VI.
• IP subnet-based VLAN: The NIC assigns a unique VLAN ID for each IP subnet it belongs
to. Therefore, the VLAN ID of outbound frames is different for different destination subnets.
An inbound frame is dropped if the IP subnet and VLAN ID do not match.
To implement this on HP-UX, you create one VI per IP subnet. In other words, you first
create as many VIs as there are subnets that you want configured on a given NIC port, and
then you configure IP addresses on their VPPAs using ifconfig.
Determining a Usage Scenario that Meets Your Network Needs
The way you decide to use VLANs in a network depends on the requirements of individual
stations in the network. If appropriate, you can even configure all three types of VLANs in a
network at the same time. The following are some guidelines for determining which type of
VLAN to configure:
• If an end-station NIC needs to belong to only one VLAN, you have two choices:
— Configure a port-based VLAN on that NIC and enable the corresponding VLAN ID on
the switch port to which the NIC is connected. This switch port must be marked “tagged”
for that VLAN ID.
— Keep that end station VLAN unaware. You just need to enable the corresponding VLAN
ID on the switch port. This switch port must be marked “untagged”.
Typically you need to do this on workstation NICs.
• If an end-station NIC needs to process frames for more than one protocol (such as IPv4,
IPv6, or IPX), configure a protocol-based VLAN on that NIC, by assigning one VLAN ID to
each protocol. You must also configure the switch port the NIC is connected to with the
same VLAN IDs and mark them “tagged” on the switch.
• If an end-station NIC must handle IP packets belonging to multiple subnets, use an IP
subnet-based VLAN. Assign a unique VLAN ID to each IP address configured on that NIC.
Enable the same VLAN IDs on the switch port to which the NIC is connected, and mark
them “tagged” on the switch.
• You can also use combinations of the three types. For example, if your end station processes
frames for more than one protocol, and it also serves multiple IP subnets, consider using
both protocol-based and subnet-based VLANs.
Priority and Class of Service (CoS)
HP-UX allows you to specify a 3-bit priority encoding (resulting in eight possible values) for
each VLAN configured on a NIC port. The VLAN tag carries this value to all the switches on the
route. Some switch vendors have implemented a priority mechanism that acts on this 3-bit
priority encoded in the VLAN tag (see Figure 2), to provide a rudimentary Class of Service (CoS)
differentiated service. For example, in the event of congestion, the switch may give a better
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