Why Is My SFP Not Working?


It’s 3 am. You’ve just finished installing your new Catalyst switches into the rack and you’re ready to turn them up and complete your cutover. You’ve been fighting for months to get the funding to get these switches so your servers can run at full gigabit speed. You had to cut some corners here and there. You couldn’t buy everything new, so you’re reusing as much of your old infrastructure as possible. Thankfully, the last network guy had the foresight to connect the fiber backbone at gigabit speeds. You turn on your switches and wait for the interminably long ASIC and port tests to complete. As you watch the console spam scroll up on your screen, you catch sight of something that makes your blood run cold:

%GBIC_SECURITY_CRYPT-4-VN_DATA_CRC_ERROR: GBIC in port 65586 has bad crc
 %PM-4-ERR_DISABLE: gbic-invalid error detected on Gi1/0/50, putting Gi1/0/50 in err-disable state

Huh?!? Why aren’t my fiber connections coming up? Am I going to have to roll the install back? What is going on here?!?

You will see this error message if you have a third party SFP inserted into the Catalyst switch. While Cisco (and many others) OEM their SFP transceivers from different companies, they all have a burned-in chip that contains info such as serial number, vendor ID, and security info like a Cyclic Redundancy Check (CRC). If any of this info doens’t match the database on the switch, the OS will mark the SFP as not supported and disable the port. The fiber connection won’t come up and you’ll find yourself screaming at terminal window at 3:30 in the morning.

Why do vendors do this? Some claim it’s vendor lock in. You are stuck ordering your modules from the vendor at an inflated cost instead of buying them from a different source. Others claim it’s to help TAC troubleshoot the switch better in case of a failure. Still others say that it’s because the manufacturing tolerances on the vendor SFPs is much better than the third party offerings, even from the same OEM. I don’t have the answer, but I can tell you that Cisco, HP, Dell, and many others do this all the time.

HP is the most curious case that I’ve run into. Their old series A SFP modules (HP calls them mini-GBICs) didn’t even have an HP logo. They bore the information from Finisar, an electroics OEM. The above scenario happened to me when I traded out a couple of HP 2848 swtiches for some newer 2610s. The fiber ports locked up solid and would not come alive for anything. I ended up putting the old switches back in place as glorified fiber media converters until I figured out that new SFPs were needed. While not horribly expensive, it did add a non-trivial cost to my project, not to mention all the extra hours of troubleshooting and banging my head against a wall.

Cisco has an undocumented and totally unsupported solution to this problem. Once you start getting the console spam from above, just enter these commands:

service unsupported-transceiver
no errdisable detect cause gbic-invalid

These commands are both hidden, so you can’t ? them. When you enter the first command, you get the Ominous Warning Message of Doom:

Warning: When Cisco determines that a fault or defect can be traced to the use of third-party transceivers installed by a customer or reseller, then, at Cisco’s discretion, Cisco may withhold support under warranty or a Cisco support program. In the course of providing support for a Cisco networking product Cisco may require that the end user install Cisco transceivers if Cisco determines that removing third-party parts will assist Cisco in diagnosing the cause of a support issue.

It goes without saying that calling TAC with a non-Cisco SFP in the slot is going to get you an immediate punt or request to remove said offending SFP. You’ll likely argue that your know the issue isn’t with the SFP that was working just fine an hour ago. They will counter with not being able to support non-Cisco gear. You’ll complain that removing the SFP will create additional connectivity issues and eventually you’ll hang up in frustration. So, don’t call TAC if you use this command. In fact, I would counsel that you should only use this command as a short term band-aid to get your out of the data center at 3 am so you can order genuine SFPs the next morning. Sadly, I also know how budgets work and how likely you are to get several hundred dollars of extra equipment you “forgot” to order. So caveat implementor.

18 thoughts on “Why Is My SFP Not Working?

  1. Pingback: Why Is My SFP Not Working?

  2. This may help with some SFPs but apparently not all. I just had a couple of non-Cisco 1000base-T SFPs that were tried on Cat4500 (remote site, components supplied by a third party). Nothing brought the links up. There were no errors or additional log entries of any kind, and service unsupported-transceiver did not help. Cisco modules worked fine. Apparently the SFP was 10/100/1000 and it just didn’t work with Cat4500. If I understood it correctly the same SFPs had worked fine with some other Cisco switches. Unfortunately I don’t have the linecard or SFP model infos here.

  3. “service unsupported-transceiver” this saved me on a WAN turnup where the SP stated the fiber run was only 5 miles. I had an IR1 but the fiber turned out to be almost 35 miles!! Luckily the install guy gave me a spare generic from his van.

    Why there was no MUX onsite was also a surprise during the project.

  4. Juniper tech support and sales don’t care about non-Juniper SFP+. That’s why I can use these third party SFP+:
    SFP+-WDM-LR/ER (10G) 10-60km. – $212-$520
    SFP+ SR-2-D 10G 1310 _2km_ for MMF – $115

  5. Yeah, and there are MGB-something SFPs from cisco’s SMB networking series which clearly state “Cisco” on them, but are not always supported by “classic” cisco gear.

    Most problems I’ve ever had with lock-ins were in multi-vendor environments: you just can’t order a bunch of same-PN SFPs with the same price (however high it is) and the same delivery date. Especially then both sides of the link are restricted – HP and Cisco…

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  9. Please help me out…
    I have Hp P 2000[storage] currently hv 12terabyte installed. This storage device unfortunately did not come with an SFP. It also has a SAS controller as one of the channels to connect to the storage. so it has both fiber [SFP and SAS]

    I also hv an Hp server, Proliant. it has fiber channels and one ethernet port .

    I connected the storage and the server using a fiber Cable, but the storage won’t show up on the server. The SFP am using for the storage is finisar, 8Gb.. The one with the server is just the same but has Hp inscription on it.

    Please I need your help. could it be compatibility issues, or there should be configurations of some sort before the storage shows up on the server.

  10. 3rd party optics are so standardized it’s rare that the issue from the switch would be caused by it. Cisco usually asks that you remove the SFP before they provide technical assistance but they will still offer support. And your warranty will still stay the same they can’t void it because you use a 3rd party optic.

  11. TRENDnet’s 100/1000Base-T to SFP Media and networking Converter, type TFC-1000MGA, is a reputable Plug-and-Play Fibre-to-Ethernet converter in a flawless form part. This multipurpose fibre converter helps each Multi-Mode (SX) as well as Single-Mode (LX) fiber qualifications for coverage ranges of maximum eighty kilometers (fifty mls).

  12. looking for brocade compatible sfp for 7600 (yes I know it’s been eol’d-still supported up to 2018)-will the above mentioned trendnet sfp suffice or do i have to take it up the tail pipe for brocades? found some 3P modules, still not sure whether to risk it

  13. We have a 2 x WS-C3750X-48 stack on IOS v15.0, we are using a Finisar GBIC for a WAN Uplink and we have been getting the following errors on SFP Slot Gb interfaces:

    Jan 26 14:09:06: %GBIC_SECURITY_CRYPT-4-VN_DATA_CRC_ERROR: GBIC in port Gi1/1/4 has bad crc
    Jan 26 14:09:06: %PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported transceiver found in Gi1/1/4

    Of course, we tried configuring:

    service unsupported-transceiver
    no errdisable detect cause gbic-invalid

    The bouncing ports and reseating cables and SFP’s to not avail.

    The key bit of information here is the fact that we’re on version 15.0, v15 does not support the above commands.

    Also if you are clutching at straws like I was and you are trying to change speed and duplex settings in an attempt to get it working, then don’t bother because if you are using GigabitEthernet SFP Slot interfaces like me, you are likely restricted in what you can change, see extract from link below: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750x_3560x/software/release/12-2_53_se/configuration/guide/3750xscg/swint.html#wp1028308

    For SFP module ports, the speed and duplex CLI options change depending on the SFP module type:
    –The 1000BASE-x (where -x is -BX, -CWDM, -LX, -SX, and -ZX) SFP module ports support the nonegotiate keyword in the speed interface configuration command. Duplex options are not supported.
    –The 1000BASE-T SFP module ports support the same speed and duplex options as the 10/100/1000-Mb/s ports.

    Long and short of it, do what you have to and get Cisco branded SFP’s!

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