Datasheet

56
Release Notes for Catalyst 4500 Series Software Release 7.x
OL-1983-28
Usage Guidelines, Restrictions, and Troubleshooting
• On trunk ports, ensure that the trunk configuration is valid on both sides of the link.
• 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 nonmulticast frames but is not receiving any BPDUs.
• To monitor blocked spanning tree ports, use these commands:
– Use the show port command to see if the port has registered many alignment, FCS, or any other
type of line errors. If these errors are incrementing continuously, the port might drop input
BPDUs.
– Use the show mac command if the Inlost counter increments continuously or a port is losing
input packets because of a lack of receive buffers. This problem can also cause the port to drop
incoming BPDUs.
• On trunk ports, ensure that the duplex is set to full on both sides of the link to prevent collisions in
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 such ports.
VTP, VLANs, and VLAN Trunks
This section contains usage guidelines, restrictions, and troubleshooting information that apply to VTP,
VLANs, and VLAN trunks:
• The VLAN numbers are always ISL VLAN identifiers and not 802.1Q VLAN identifiers.
• A VTP transparent switch with no VTP domain name configured might not relay VTP requests
received from VTP client and server switches. Therefore, VTP client and server switches might not
synchronize if they are separated by a VTP transparent switch with no domain name configured.
Workaround: Configure a VTP domain name on the VTP transparent switch.
• Although the Dynamic Trunk Protocol (DTP) is a point-to-point protocol, some internetworking
devices might not forward DTP frames. To avoid connectivity problems, follow these guidelines:
– For ports connected to non-Catalyst series devices in which trunking is not being used,
configure trunk-capable Catalyst 4500 series switch ports to off by entering the set trunk
mod_num/port_num off command.
– When trunking to a Cisco router, use the set trunk mod_num/port_num nonegotiate command.
The nonegotiate keyword transitions a link into trunking mode without sending DTP frames.
• With Cisco IOS Release 12.0, the Catalyst 8510 campus switch router (CSR) does not process
untagged packets (packets on the native VLAN) received on an IEEE 802.1Q-trunked interface (all
such packets are dropped). If you configure Catalyst 8510 CSR subinterfaces to a trunk using
802.1Q encapsulation, traffic cannot be carried successfully on the native VLAN for the trunk
configured on a Catalyst 4500 series switch.
Workaround: Create an unused VLAN and assign it as the native VLAN for the 802.1Q trunk on
the Catalyst 4500 series switch. Verify the native VLAN assignment for the trunk using the show
trunk command.
This problem is tracked as a defect against the Catalyst 8510 CSR software. (CSCdk77676)