Document ID: RDWR-ALOS-V2900_AG1302
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Chapter 4 – VLANs
This chapter describes network design and topology considerations for using Virtual Local Area
Networks (VLANs). VLANs are commonly used to split groups of network users into manageable
broadcast domains to create logical segmentation of workgroups, and to enforce security policies
among logical segments.
The following topics are addressed in this chapter:
•
—This section discusses VLANs with VLAN ID numbers.
•
—This section discusses VLAN tagging.
•
VLANs and the IP Interfaces, page 82
—This section briefly describes how management
functions can only be accomplished from stations on VLANs that include an IP interface to
Alteon.
•
VLAN Topologies and Design Issues, page 82
—This section discusses how you can logically
connect users and segments to a host that supports many logical segments or subnets by using
the flexibility of the multiple VLAN system.
•
VLANs and Default Gateways, page 85
—This section discusses associating gateways to VLANs.
Notes
•
Basic VLANs can be configured during initial configuration. For more information, see Using the
Setup Utility in the Alteon Application Switch Operating System Command Reference.
•
More comprehensive VLAN configuration can be done from the CLI. For more information, see
VLAN Configuration, as well as Port Configuration, in the Alteon Application Switch Operating
System Command Reference.
VLAN ID Numbers
Alteon supports up to 2048 VLANs per Alteon. Even though the maximum number of VLANs
supported at any given time is 2048, each can be identified with any number between 1 and 4090.
VLANs are defined on a per-port basis. Each port on Alteon can belong to one or more VLANs, and
each VLAN can have any number of ports in its membership. Any port that belongs to multiple
VLANs, however, must have VLAN tagging enabled (see
).
Each port has a configurable default VLAN number, known as its PVID. The factory default value for
all PVIDs is 1. This places all ports on the same VLAN initially, although each PVID is configurable to
any VLAN number between 1 and 4090.
Any untagged frames (those with no VLAN specified) are classified with the sending port's PVID.
VLAN Tagging
Alteon supports 802.1Q VLAN tagging, providing standards-based VLAN support for Ethernet
systems.
Tagging places the VLAN identifier in the frame header, allowing multiple VLANs per port. When you
configure multiple VLANs on a port, you must also enable tagging on that port.
Because tagging fundamentally changes the format of frames transmitted on a tagged port, you
must carefully plan the design of a network to prevent transmission of tagged frames to devices that
do not support 802.1Q VLAN tags.
