HP-UX VLAN Administrator's Guide, February 2007

The usage type of the HP-UX VLAN configured on a NIC port depends on how you create and
configure the VLAN interfaces. Here are some examples:
• For a port-based VLAN: You create just one VLAN interface on a given NIC port. All
protocols and applications use this VLAN interface's VPPA to transmit data traffic. Therefore,
all frames transmitted by that NIC port are tagged with the VLAN ID of that VLAN interface.
• For a protocol-based VLAN: You create one VLAN interface per Layer 3 protocol processed
by the NIC. You then configure the protocol (for example, ifconfig) using the VPPA of
each VLAN interface.
• For an IP subnet-based VLAN: You create one VLAN interface for every subnet that you
want configured on a given NIC port, and then you configure IP addresses on their VPPAs
using ifconfig.
Comparing Properties of VPPAs and PPAs in HP-UX VLANs
When an HP-UX VLAN is created on a given LAN card port, the system generates a virtual PPA,
or VPPA, which can be used to send and receive 802.1Q tagged frames on that LAN card. Each
HP-UX VLAN has a VPPA associated with it. A VPPA has essentially the same properties as a
physical point of attachment (PPA) on a LAN card. After an HP-UX VLAN is created, its VPPA
can be used to configure protocols, send commands, and transmit and receive data just like a
PPA.
The key differences between a VPPA and a PPA are as follows:
• A VPPA is associated with an HP-UX VLAN, the properties of which are determined by
add (or modify) HP-UX VLAN actions. The PPA of a physical interface does not have an
HP-UX VLAN associated with it.
• An HP-UX VLAN does not have a unique hardware instance. VPPA values are assigned
such that they do not overlap with hardware instance numbers of physical interfaces on the
system. The PPA assigned to a LAN card port is the same as its hardware instance number.
• An HP-UX VLAN shares all the link properties (such as speed, duplexity, MTU, and MAC
address) of the physical interface on which it is configured. Any changes to the underlying
physical interface propagate to all its associated VPPAs.
Correspondingly, you cannot change such physical link properties as speed, duplexity, or
maximum transmission unit (MTU) over an HP-UX VLAN. If you make changes to a physical
interface, those changes are reflected in the HP-UX VLANs configured on that interface.
• All frames transmitted via a VPPA are VLAN tagged. Frames transmitted via a physical
PPA are sent untagged.
Promiscuous Mode Characteristics and HP-UX VLANs
Promiscuous mode is a mode of operation in which every data packet transmitted can be received
and read by a network adapter. Promiscuous mode is often used to monitor network activity.
When considering promiscuous-mode characteristics and HP-UX VLANs, note the following:
• Only one stream can run in the unbound promiscuous mode per physical interface and in
all the HP-UX VLAN interfaces created over it.
• A promiscuous stream on the physical interface detects all the frames transmitted or received
on the physical LAN card port, both tagged and untagged frames.
• A promiscuous stream on an HP-UX VLAN interface detects only tagged frames with the
same VLAN ID as that of the HP-UX VLAN interface.
Priority, ToS, and Override Settings in HP-UX VLANs
IP packets are classified and marked into different priority levels. The markings are transported
through a type of service (ToS) octet in the IPv4 header and a traffic class field in the IPv6 header.
Overview of VLANs 21