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Error's in Switch 6509 ?


We have a core switch (Catalyst 6509) with 8 Port Fiber Module, 96 Port RJ-45 Module & 16 Port RJ-45 GB Module.

All the server's are connected to RJ45 Port

(100 Mbps-Auto-Full Duplex). All these servers are connected to these ports.

We have Veritab Backup Device & this is connected to RJ45- GB Port & 3 Important Servers are connected to RJ45 GB Module.

They below ports are getting some errors:

Port 9/14-16, 5/12-13, 5/7-11

The Errors are: FCS-Err , Runts , Align-Err


Why these errors are coming in?

What is the problem ?

Will these errors aftect the Backup process ??

Note:The backup is very slow now a days

Please reply


VIP Purple

Re: Error's in Switch 6509 ?

Hello Sriram,

are any of the ports on which the errors occur operating in half duplex mode ?

When operating at half-duplex setting, some data link errors such as Frame Check Sequence (FCS), alignment, runts, and collisions are normal. Generally, a one percent ratio of errors to total traffic is acceptable for half-duplex connections. If the ratio of errors to input packets is greater than two or three percent, performance degradation may be noticed.

In half-duplex environments, it is possible for both the switch and the connected device to sense the wire and transmit at exactly the same time and result in a collision. Collisions can cause runts, FCS, and alignment errors due to the frame not being completely copied to the wire which results in fragmented frames.

When operating at full-duplex, FCS, Cyclic Redundancy Checks (CRC), alignment errors, and runt counters should be minimal. If the link is operating at full-duplex, the collision counter is not active. If the FCS, CRC, alignment, or runt counters are incrementing, check for a duplex mismatch. Duplex mismatch is a situation where the switch is operating at full-duplex and the connected device is operating at half-duplex, or vice versa. The result of a duplex mismatch will be extremely slow performance, intermittent connectivity, and loss of connection. Other possible causes of data link errors at full-duplex are bad cables, faulty switch port, or NIC software/hardware issues.

There is a Cisco document that describes interoperability problems between Catalyst switches and certain NIC types, might be worth checking out:

Troubleshooting Cisco Catalyst Switches to NIC Compatibility Issues



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