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Community Member

What causes the "False carrier errors" counter to increment?


on several 2950 Catalysts I see on most interfaces that the "False carrier errors" is counter rather high. The rest of the counters look allright to me.

Port configuration is as follows:

interface FastEthernet0/2

switchport access vlan 5

switchport mode access

speed 100

duplex full

no snmp trap link-status

spanning-tree portfast

spanning-tree bpduguard enable

This is the output you get from the "show controllers ethernet-controllers" command:

Transmit FastEthernet0/2 Receive

709814271 Bytes 2445719693 Bytes

392128521 Frames 90436937 Frames

158965864 Multicast frames 1 FCS errors

54959496 Broadcast frames 3546 Multicast frames

0 Pause frames 114443 Broadcast frames

0 Single defer frames 0 Control frames

0 Multiple defer frames 0 Pause frames

0 1 collision frames 0 Unknown opcode frames

0 2-15 collisions 0 Alignment errors

0 Late collisions 0 Length out of range

0 Excessive collisions 5 Symbol error frames

0 Total collisions 1049 False carrier errors

0 Control frames 0 Valid frames, too small

2 VLAN discard frames 0 Valid frames, too large

0 Too old frames 10 Invalid frames, too small

0 Tagged frames 0 Invalid frames, too large

2 Aborted Tx frames 0 Discarded frames


Re: What causes the "False carrier errors" counter to increment?

Here's a quote from the Switch Command Reference which describes the "False Carrier Errors" counter. It doesn't give much information, but maybe it helps!

"The number of occurrences in which the interface detects a false carrier when frames are not sent or received."

I can't find any more information on the web about the errors, and i haven't seen the errors before so i can't tell you more about it.



Community Member

Re: What causes the "False carrier errors" counter to increment?

Thanks Michael

This was as far as I got - and to be honest I can't make out what Cisco means by a "false carrier". Since the interface is configured full duplex there is no CSMA/CD in use. And the rest of the error counters look (almost) zero to mee.

I'd been searching the web too, but didn't find anything useful.

Thanks anyway

Community Member

Re: What causes the "False carrier errors" counter to increment?

Could it be that the PC's interface is not set to FULL/100, but to Auto/Auto?

I'm also looking for the detailed meaning of "False Carrier Errors"...

Community Member

Re: What causes the "False carrier errors" counter to increment?


If the end device's interface is in Auto mode and the switch interface is fixed, you will see errors on the switch's receive counter (Alignment errors, FCS Errors, Collision Fragments). This I had already verified.

The False Carrier Error must be triggered by something else. So, having posted my original question in 2008 I'm still none the wiser.

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