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Copper SFP Link issues with 3750G-12

Hi all,

Looking for some assitance here, as I have an issue that's driving me nuts.

We have a campus network with a 4506 as the core with OM3 fibre links to dual distribution switches (one on the 4th floor of each wing, and one on the ground floor).

The distribution switches are Catalyst 3750G-12S-E, using 1000BaseT Copper Modules. From each distribution location we have Cat6a copper links to each floor.

Each floor has it's own wiring cabinet with 2 x 3560-48PS-S access switches. Each access switch is dual homed to the ground floor distribution and 4th floor distribution switches.

The problem is the physical link status of the SFP modules, primarily the ones in the 3750G. When the distribution switches are rebooted, we only get link back on about 30%-40% of the links.

I have swapped GBIC's (SFP's) between switches, tried 1000-Full configuration to disable auto-negitiation, tried mdix-auto on/off (one end and both ends), straight through cables and crossover cables. Also the patch cables we are using are Systimax 10G.

There seems to be no ryhme or reason to which links will fail, and if you remove the GBIC and back to back them in a standalone switch, they work, just not in the 3750G's.

There are 8 3750G's and we have purchased over 160 SFP modules. This is not an STP issue, as the link never gets up/up and in some cases, we see no GBIC inserted ion the 3750G interface.

I can't beleive we have multiple failed SFP modules.

Any help would be appreciated, sorry for the long winded post!



Re: Copper SFP Link issues with 3750G-12

Personally, I am always a bit reluctant about using UTP in backbonelinks just because this kind of problems. Your cabling might be suffering from EM interference due to nearby power cables or elevator shafts. Very little to do about this except using fiber instead.

Anyway, it's a nasty problem indeed. What state are the interfaces in after a reboot?

Please check the link below:

The following might be useful also:



Re: Copper SFP Link issues with 3750G-12

Bill, I also found the following in the release notes for v12.2(40):

When a Catalyst 3750-12S switch boots up, ports 1, 2, 5, 6, 9, and 10 can become active before the Cisco IOS software loading process is complete. Packets arriving at these ports before the switch software is completely loaded are lost. This is a hardware limitation when the switch uses small form-factor pluggable (SFP) modules with copper connections.

The workaround is to use switch ports other than those specified for redundancy and for applications that immediately detect active links. (CSCeh70503)

The link:

Do not know if you are running this version but it might help.