Avoiding Autonegotiation Mismatches; Gbic Security And Identification - Cisco WS-C2955T-12 Software Manual

Avoiding Autonegotiation Mismatches

Avoiding Autonegotiation Mismatches
The IEEE 802.3u autonegotiation protocol manages the switch settings for speed (10 Mbps or
100 Mbps) and duplex (half or full). Sometimes this protocol can incorrectly align these settings,
reducing performance. A mismatch occurs under these circumstances:
•
•
To maximize switch performance and ensure a link, follow one of these guidelines when changing the
settings for duplex and speed:
•
•
If a remote Fast Ethernet device does not autonegotiate, configure the duplex settings on the two ports
Note
to match. The speed parameter can adjust itself even if the connected port does not autonegotiate. To
connect to a remote Gigabit Ethernet device that does not autonegotiate, disable autonegotiation on the
local device, and set the duplex and flow control parameters to be compatible with the remote device.

GBIC Security and Identification

Cisco-approved Gigabit Interface Converter (GBIC) modules have a serial EEPROM that contains the
module serial number, the vendor name and ID, a unique security code, and cyclic redundancy check
(CRC). When a GBIC module is inserted in the switch, the switch software reads the EEPROM to check
the serial number and the vendor name and ID, and to recompute the security code and CRC. The switch
shuts down the interface and displays a GBIC_SECURITY error message if the GBIC serial number, the
vendor name or ID, the security code, or CRC is invalid.
If you are using a non-Cisco approved GBIC module, remove the GBIC module from the switch, and
Note
replace it with a Cisco-approved module. For the GBIC modules supported on the switch, refer to the
release notes (http://www.cisco.com/univercd/cc/td/doc/product/lan/c2900xl/index.htm).
After inserting a Cisco-approved GBIC module, use the show interface user EXEC command or the
show tech-support privileged EXEC command to verify the port status.
Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
9-8
A manually set speed or duplex parameter is different from the manually set speed or duplex
parameter on the connected port.
A port is set to autonegotiate, and the connected port is set to full duplex with no autonegotiation.
Let both ports autonegotiate both speed and duplex.
Manually set the speed and duplex parameters for the ports on both ends of the connection.
Chapter 9 Troubleshooting
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