Green/Amber alternating link lights

[kmataranglo]

Hi everyone,

I have a client using 2 stacked 3750s connecting via etherchannel to a 4006 and they are getting like every 2 minutes alternating green/amber link lights on one of the etherchannel ports on the 3750.

Also, we are seeing CRC errors on the interface as well. I have suggested that we swap out the gbics and fiber cable, but customer can not do this yet. After researching the issue alittle I am wondering what are some of the common causes for link faults and improperly formed packets. Is this a physical layer problem normally or could it be something else?

Has anyone else seen something like this and if so, what was the cause? He has the 3750s stacked and another thing he is doing is cabling the gec to one uplink port in each switch. STP causing this? I wouldn't think so but I am open to any ideas or comments..

Thanks

[skarundi]

According to the 3750 Configuration Guide, the alternating green/amber link status means that there is a "Link fault. Error frames can affect connectivity, and errors such as excessive collisions, CRC errors, and alignment and jabber errors are monitored for a link-fault indication.".

As you stated, most of the time this is usually a gbic or fibre malfunction. Replace the gbics first. Usually I replace the gbics on both sides on the link because either one of the gbics could result in the 3750 reporting CRC/FCS errors. if this doesn't resolve the problem, replace and/or test the fibre between the 2 devices.