User's Manual

570 CHAPTER 13: VLAN MANAGEMENT
Key Considerations The following section describes some of the key considerations for 3Com
Network Director VLAN support.
Guidelines for
creating/editing a
VLAN
Before using the Create VLAN wizard or the Edit Port VLAN Membership
wizard you should ensure that your network map is up to date. The
correct operation of these wizards depends upon the network map being
accurate. Even though 3Com Network Director checks that the basic
configuration of a switch hasn’t changed since the map was last updated
before creating or editing VLANs, 3Com Network Director does not check
whether the topology of the network has changed.
Troubleshooting Incorrect VLAN membership inference
As described in section “
VLAN membership inference” on page 509,
3Com Network Director will infer the VLAN membership of devices such
as end-stations, based upon the nearest switch port that has VLANs
configured. In some cases 3Com Network Director may get this inferred
VLAN membership wrong. For example:
■ If there is an inconsistent VLAN IDs misconfiguration then the VLAN
membership that 3Com Network Director infers might not be as
expected. See section “
Inconsistent VLAN IDs” on page 535 for
further information.
■ If there are non-3Com switches on which a VLAN is configured, the
membership of this VLAN may not be correctly inferred. 3Com
Network Director does not read the VLAN configuration from
non-3Com switches.
■ 3Com Network Director topology of the network may be inaccurate –
VLAN membership inference is dependent upon 3Com Network
Director’s model of the network topology being correct.
VLAN-related
network discovery
problems
Incorrect topology if all subnets are not discovered at once
If you are using VLANs you should discover all of your subnets in the one
network discovery operation. For further information see “
Discovering
the Network” on page 91. If you discover your subnets using multiple
discovery operations, the network topology that 3Com Network Director
displays may not be correct. For example, consider the following
network: