HP Network Direr Software Products manual Troubleshooting Incorrect Vlan membership inference

570CHAPTER 13: VLAN MANAGEMENT

Key Considerations The following section describes some of the key considerations for 3Com Network Director VLAN support.

Guidelines for Before using the Create VLAN wizard or the Edit Port VLAN Membership creating/editing a wizard you should ensure that your network map is up to date. The

VLAN 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

VLAN-related network discovery problems

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.

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: