Installation guide

79
Release Notes for Catalyst5000 Family Software Release4.x
OL-2306-01
Usage Guidelines, Restrictions, and Troubleshooting
Transceivers
This section contains usage guidelines, restrictions, and troubleshooting information that apply to
transceivers.
• If you experience trouble with a port that has an MII transceiver attached to it, check that the
transceiver jumpers are set properly.
• If an MII transceiver is plugged in at an angle, the Catalyst5000 family switch might stop
transmitting data. To recover, reseat the MII transceiver so that it is not seated at an angle. If the
Catalyst5000 family switch still cannot transmit data, disable and then reenable the port.
• If you are using MII transceivers, make sure that you are using compliant MII transceivers. Enter
the show portreg command for each MII port to ensure that the value 2100 appears in the first
column of output, as shown in the following example:
Console> (enable) show portreg 1/1
Port/PHY registers for 1/1
0x00: 2100 780F 2000 5C00 0081 0000 0000 0000
.
.
.
Console> (enable)
If you see a value of 0xffff instead of 2100, do not use the MII transceiver. An MII transceiver whose
value is set to 0xffff can prevent the Catalyst5000 family switch from receiving on this MII port,
which can cause spanning tree loops.
Check the disconnect counter register (DCR) and the False Carrier Sense Counter register (FCSCR).
These registers should remain at 0 (except for the moment at which the link comes up). A value other
than 0 indicates a physical layer problem (most likely a problem with the transceiver).
Spanning Tree
The Spanning Tree Protocol (STP) blocks certain ports to prevent physical loops in a redundant
topology. On a blocked port, the Catalyst5000 family switch receives spanning tree bridge protocol data
units (BPDUs) periodically from its neighboring Catalyst5000 family switch. You can configure the
frequency with which BPDUs are received by entering the set spantree hello command (the default
frequency is set to twoseconds). If a Catalyst5000 family switch does not receive a BPDU in the time
period defined by the set spantree maxage command (20 seconds by default), the blocked port
transitions to the listening state, the learning state, and to the forwarding state. As it transitions, the
Catalyst5000 family switch waits for the time period specified by the set spantree fwddelay command
(15seconds by default) in each of these intermediate states. Therefore, a blocked spanning tree port
moves into the forwarding state if it does not receive BPDUs from its neighbor within approximately 50
seconds.
This section contains usage guidelines, restrictions, and troubleshooting information that apply to
spanning tree.
• Connectivity between certain Token Rings might not be possible in a redundant ISL network if a
Token Ring or ATM link is the forwarding path to the root switch instead of an ISL link. Ensure that
spanning tree path costs are configured such that a Token Ring or ATM link can never have a lower
cost to the root bridge than an ISL link in the same switch. (CSCdk87396)