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Catalyst2950 and Catalyst2955 Switch Software Configuration Guide
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Chapter32 Troubleshooting
Preventing Autonegotiation Mismatches

Recovering from Lost Member Connectivity

Some configurations can prevent the command switch from maintaining contact with member switches.
If you are unable to maintain management contact with a member, and the member switch is forw arding
packets normally, check for these conflicts:
•A member switch (Catalyst 3550, Catalyst 3500 XL, Catalyst 2955, Catalyst 2950, Catalyst 2940,
Catalyst 2900XL, Ca talyst 2820, and Catalyst 1900) canno t connec t to the comma nd switch
through a port that is defined as a network port.
•Catalyst 3500 XL, Catalyst 2900 XL, Catalyst 2820, and Catalyst 1900 me m ber s witc hes m ust
connect to the command switch through a port that belongs to the same management VLAN.
•A member switch (Catalyst 3550, Catalyst 3500 XL, Catalyst 2950, Catalyst 2940,
Catalyst 2900XL , Catalyst 2820, and Catalyst 1900) con nected to the command switch thr ough a
secured port can lose connectivity if the port is disabled because of a s ecu rity viol at ion.
Preventing Autonegotiation Mismatches
The IEEE 802.3ab autonegotiation protocol manages the switch settings for speed (10 Mbps, 10 0 Mbps,
and 1000 Mbps excluding GBIC ports) and duplex (half or full). T here are situations when this protocol
can incorrectly align these settings, reducing performance. A mismatch occurs unde r these
circumstances:
•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.
To maximize switch performance and ensure a link, follow one of these guidelines when changing the
settings for duplex and speed:
•Let both ports autonegotiate both speed and duplex.
•Manually set the speed and duplex parameters for the ports on both ends of the connection.
Note If a remote device does not autonegotiate, configure the duplex settings on the two por ts to ma tc h. The
speed parameter can adjust itself even if the connected port does not autonegotiate.
GBIC and SFP Module Security and Identification
Cisco-approved Course Wave Division Multiplexer (CWDM) Gigabit Interface Converter (GBIC) and
small form-factor pluggable (SFP) 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
CWDM GBIC or SFP module is inserted in the switch, the switch software reads the EEPROM to check
the serial number, vendor name and vendor ID, and recompute the security code and C RC. If the se r ial
number, the vendor name or vendor ID, the security code, or CRC is invalid, the switc h p lac es the
interface in an error-disabled state.
Note If you are using a non-Cisco approved CWDM GBIC or SFP module, remove the GBIC or SFP module
from the switch, and replace it with a Cisco-approved module.