18-9
Troubleshooting
Unusual Network Activity
Troubleshooting
Problems Related to Spanning-Tree Protocol (STP)
Caution If you enable STP, it is recommended that you leave the remainder of the STP
parameter settings at their default values until you have had an opportunity
to evaluate STP performance in your network. Because incorrect STP se ttings
can adversely affect network performance, you should avoid making chang es
without having a strong understanding of how STP operates. To learn the
details of STP operation, refer to the IEEE 802.1d standard.
Broadcast Storms Appearing in the Network. This can occur when
there are physical loops (redundant links) in the topolo gy.Where this exists,
you should enable STP on all bridging devices in the top ology in order for the
loop to be detected.
STP Blocks a Link in a VLAN Even Though There Are No Redundant
Links in that VLAN. In 802.1Q-compliant switches such as the Switch
4108GL, STP blocks redundant physical links even if they are in separate
VLANs. A solution is to use only one, multiple-VLAN (tagged) link between
the devices. Also, if ports are available, you can improve the band width in this
situation by using a port trunk. See “STP Operation with 802.1Q VLANs” on
page 16-12.
Stacking-Related Problems
The Stack Commander Cannot Locate any Candidates. Stacking oper-
ates on the primary VLAN, which in the default configuration is the
DEFAULT_VLAN. However, if another VLAN has been configured as the
primary VLAN, and the Commander is not on the primary VLAN, then the
Commander will not detect Candidates on the primary VLAN.
TACACS-Related Problems
Event Log. When troubleshooting TACACS+ operation, check the switch’s
Event Log for indications of problem areas.
All Users Are Locked Out of Access to the Switch. If the switch is func-
tioning properly, but no username/password pairs result in console or Telnet
access to the switch, the problem may be due to how the TACACS+ server
and/or the switch are configured. Use one of the following methods to recover:
■Access the TACACS+ server application and adjust or remove the
configuration parameters controlling access to the switch.