Receiving FCS-Err on Cisco catalyst 6500

Unanswered Question
Jun 6th, 2010

When I am checking Sh Port on Cisco Catalyst 6500 I am getting FCS-Err 18360 on port 3/1.

Port 3/1 is connected with another Catalyst 6500 through single mode fiber on another location.

I am facing ping break issues and slow network complains from user.

I have this problem too.
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Hitesh Vinzoda Sun, 06/06/2010 - 23:38


This is typically a physical issue (such as cabling, a bad port, or a bad Network Interface Card (NIC)) but can also indicate a duplex mismatch.


Hitesh Vinzoda

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rajatsetia Mon, 06/07/2010 - 04:02


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 in which the switch is
operating at full-duplex and the connected device is operating at half-duplex, or the other way around. The result of a duplex mismatch is extremely slow performance,
intermittent connectivity, and loss of connection. Other possible causes of data link errors at full-duplex are bad cables, a faulty switch port, or NIC software or hardware


FCS is layer 1 issues and few general causes are

- Mismatch of SFP type on both ends

- Dirty fiber connector or SFP

- Faulty termination of fiber

- Mismatch in cable type i.e. patch cable is different from optical fiber running between patch panels

- Mismatch of duplex


- try switchport nonegotiate

- hardcode the duplex setting to full

- try using different SFP or switch ports

- use optical TDR to test the end to end connectivtiy

Hope it helps

Kind Regards,


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