Design Guidelines - 3Com 4007 Implementation Manual

Key Guidelines for Implementation 253

Design Guidelines

Before you create any VLANs, draw your chassis configuration and
carefully identify how the VLANs that are associated with your
modules are bridging (or, for Multilayer Switching Modules, bridging
or routing). Remember that each VLAN constitutes a subnetwork. If a
VLAN spans modules, each participating module must have its
attached devices (and router interface, if applicable) configured for
that subnetwork. Use your drawing to help you identify the
configuration requirements for each port in a VLAN and to ensure that
the switch fabric module is configured to pass traffic to the correct
VLANs.
To simplify your configuration, try to keep the number of VLANs as
small as possible. Where possible, reduce the number of subnetworks.
To ease configuration changes (such as moving a module to another
slot while retaining the same VLAN configurations), you can use the
staging option. To use this option, enable staging on the module by
issuing the command and use the EME
module nvData staging
option to apply the configuration. You can also use EME
staging
commands to upload and download module configurations saved on
a server. See the Switch 4007 Enterprise Management Engine User
Guide for more information about the EME.
If you lose track of your changes in a complicated VLAN configuration,
it may be better to perform a nonvolatile data (nvData) reset operation
than to make numerous VLAN changes. For example, you can use the
command to return to a default module
module nvData reset
configuration, including the VLAN configuration. See Chapter 6 for
more information.
Evaluate whether you really need to use tagging on the front-panel
ports of your switching modules. If you do need to tag front-panel
ports in your user-configured VLANs, then your attached devices must
be IEEE 802.1Q enabled.
In general, tag the backplane ports of the switching modules and the
corresponding switch fabric module ports when you define multiple
VLANs that span modules (for bridging or routing). When multiple
VLANs are defined across the backplane ports and switch fabric
module ports, only one VLAN can be untagged and all others must be
tagged.