14-2
Catalyst 2950 Desktop Switch Software Configuration Guide
78-11380-03
Chapter14 Troubleshooting
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:
• 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 Fast Ethernet device does not autonegotiate, configure the duplex settings on the two ports
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.
Table 14-1 Conflicting Features
Port Group Port Security
SPAN
Source Port
SPAN
Destination Port
Connect to
Cluster?
Protected
Port 802.1X Port
Port Group
– No Yes No Yes Yes No
Port Security
No – Yes No Yes No No
SPAN Source Port
Yes Yes – No Yes Yes
1
Yes
SPAN Destination
Port
No No No – Yes Yes No
Connect to Cluster
Yes Yes Yes Yes – Yes –
Protected Port
Yes No Yes
1
Yes
1
1. Switch Port Analyzer (SPAN) can operate only if the monitor port or the port being monitored is not a protected port.
Yes ––
802.1X Port
No No Yes No –––
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