Installation guide

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Release Notes for Catalyst5000 Family Software Release4.x
OL-2306-01
Usage Guidelines, Restrictions, and Troubleshooting
• A Catalyst family switch should be the root for all VLANs, especially VLAN1. In order to recover
from an extended broadcast storm caused by a faulty device in a network, Catalyst family switches
reset blocked ports. To ensure recovery, all Catalyst family switches in the network should perform
this function at the same time by sending synchronization packets on VLAN 1. These
synchronization packets are only sent by a Catalyst family switch if it is the root bridge.
• Use the most-powerful possible supervisor engine version for the root node (for example,
Supervisor Engine III instead of Supervisor Engine II).
• On a switch with Supervisor Engine III or III F with a NFFC or NFFC II, you cannot enable or
disable spanning tree on a per-VLAN basis. You must enable or disable spanning tree on every
VLAN using the set spantree enable all and set spantree disable all commands.
• In software release 4.x and later, the uplink ports on the standby supervisor engine are active (in
software release 4.3(1) and later you can disable this feature). If you are using the ports on the
standby supervisor, and you have configured those ports as trunk ports, make sure that traffic for no
more than 20 different VLANs will traverse the trunk.
Caution If traffic for more than 20 VLANs is carried on standby supervisor engine trunk ports, under certain
conditions, network loops can temporarily open, increasing spanning tree convergence time and
network instability.
• After a switchover from the active to the standby supervisor engine, the ports on the standby
supervisor engine take 20seconds to recover if spanning tree is disabled or PortFast is enabled on
those ports. Other ports on the switch take from 5 to 15seconds to recover if spanning tree is
disabled or PortFast is enabled on those ports.
• Disabling spanning tree on the native VLAN of an IEEE 802.1Q trunk can potentially cause
spanning tree loops. We recommend that you leave spanning tree enabled on the native VLAN of
an 802.1Q trunk. If you plan to disable spanning tree in an 802.1Q environment, disable spanning
tree on every VLAN in the network and ensure a loop-free topology exists.
• Use these commands to monitor blocked spanning tree ports:
– show port—Check to see if the port has registered a lot of alignment, FCS, or any other type
of line errors. If these errors are incrementing continuously, the port might drop input BPDUs.
– show mac—If the Inlost counter is incrementing continuously, the port is losing input packets
because of a lack of receive buffers. This problem can also cause the port to drop incoming
BPDUs.
• On a blocked spanning tree port, make sure that the Rcv-Frms and Rcv-Multi counters are
incrementing continuously. If the Rcv-Frms counter stops incrementing, the port is not receiving
any frames, including BPDUs. If the Rcv-Frms counter is incrementing but the Rcv-Multi counter
is not, then this port is receiving non-multicast frames but is not receiving BPDUs.
• On a blocked spanning tree port, check the duplex configuration to ensure that the port duplex is set
to the same type as the port of the neighboring device.
• On trunk ports, make sure that the trunk configuration is set properly on both sides of the link.
• On trunk ports, make sure that the duplex is set to full on both sides of the link to prevent any
collisions under heavy traffic conditions.
• Do not use spanning tree PortFast on a trunk port. Although the show spantree command displays
PortFast as enabled on a trunk port, PortFast has no effect on trunk ports.
• IEEE STP between a Cisco router and Catalyst5000 family ATM LANE module over RFC 1483
PVCs does not function properly.