Version 6 SuperStack 3 Switch 4400 Management Interface Reference Guide

Support - Problem Solving - VLAN Problems
http://support.3com.com/infodeli/tools/switches/4400/DHA1720-3AAA08/htm/support/problemsolving/vlanproblems.htm[11/15/2010 3:43:56 PM]
Support
Problem Solving
VLAN Problems
No traffic will pass between the VLANs, or endstations cannot
connect to a server on a different VLAN.
To allow different VLANs on the same Switch to communicate with each
other, there are several different options, most of which use some form
of tagging.
The Switch supports 802.1Q tagging. Both sides of the link,
however, must support tagging, so if you want endstations on
different VLANs to connect to a single server, then the Network
adapter card in the server must also support 802.1Q tagging
(3Com's 3C980 server NIC supports this).
It is also possible to connect the Switch to a layer 3 Switch that
supports 802.1Q tagging. This will enable you to provide VLAN
routing capabilities for the Switch.
When operating in a layer 3 environment, it is possible that traffic
is blocked by a deny rule in the access list. Check the access list
for any deny rules that maybe blocking the traffic.
Check that the network traffic does support the IP protocol. If it
is not IP traffic, you will need an external layer 3 device that
does support the appropriate protocol.
For further details about configuring VLANs, refer to the Implementation
Guide on the CD-ROM that accompanies your Switch or on the 3Com
Web site.
You have specified that an endstation generates traffic that has a
high priority, but when it passes through the network this priority
information is lost.
The endstation is attached to a Switch port using an untagged VLAN
connection, and the Switch is removing the priority information when it
is forwarded to other untagged ports. To maintain the priority
information, specify that all untagged Switch ports use 802.1Q tagging.
You have placed two or more Switch units in a stack, and some
ports have lost their VLAN allocations and been disabled.
The Switch units had more than the maximum number of VLANs
defined between them, and these extra VLANs were removed when the
units were stacked. If a port was allocated to one of these VLANs
among others, it lost that particular VLAN allocation. If a port only
belonged to removed VLANs, it lost all its VLAN allocations and was
disabled. Re-enable the disabled ports, and place them in the remaining
VLANs.
You have connected a Switch to a device using an 802.1Q tagged
link, and you can no longer access the management software of
the device or the devices connected to that device.
You may have connected to a device that only supports 802.1Q tagged
links and have not specified that VLAN 1 traffic uses 802.1Q tagging.
Specify that VLAN 1 traffic is 802.1Q tagged, and try accessing the
devices again.