Tuesday, April 23, 2013

TIP: Incompatible SFP/SFP+ cisco

In this blog I will  demonstrate what happens when a SFP that's not compatible, are installed into a  cisco switch or router.

1st here's the switch type that I'm demo'ing this on.

Next, we will install a inferior SFP optical transceiver;  1gig SFP MM . And you will notice the port will go into err-disabled and cisco will log this;

Okay let's stop here and see why we get this. Per cisco, they don't like or allow anybody else  SFP/SFP+. Here's the quote from cisco website on how the checks works;


Basically they have a eprom that contains a crc code and serial information and when cisco runs the check, they fail and the SFP is marked incompatible.

Here's a list of SFP  that are supported.


Now I know of one vendor that seems to make vendor neutral  optics.


So if you have to use a 3rd party optics or don't want to buy cisco new prices, look at transition and call them up. btw: I used to work for one of their sister company. Transition networks has always been an alternatiev optic vendor. I have not used any of their SFP+ optics, but their 1gig stuff is solid.

Okay so now when we install the correct SFP into a cisco switch, it 's now happy and dorky and ready to go.

I 've worked on numerous projects and deals, where the cost of the optics and any conversion , became the deal breaker.


 Xenpak to Xenpak2 to SFP+



Almost all new network gear are moving to the Small Form Pluggable format. And it's a big forklift  ( $$$$.$$ )  from path-cables and optics to refresh your network or DataCenter from one type to another. In one client that did a refresh, they spent over 30K in patch cables alone,  with moving from the SC-SC to LC-SC interfaces cables, &  across 30 sites and on two continents. 

btw: I can help and consult on matters related to this example.

Cisco and most other vendors , does; "  the buy my optics  &  only my optics",  only due to any of the below factors;
  • to ensure you buy a quality transceiver
  • to eliminate any tac support case due to hardware issues related to a 3rd party
  • to make money with the customer, &  buying  the cisco branded product
  • to eliminate any knock offs or fakes

Now you will be surprised to find ,  that the SFPs in use today, are made normally by a handful of vendor and they make these across the board for all network/server suppliers.


  • Finisar
  • Stratos
  • Shenzhen
  • etc..

In fact, they make one round for vendor X  and then another round for vendor Y and so on. And if I had to guess, it comes from the same chinese shop.

Now with all of the above said, I want to show you some interesting things pertaining to  SFP transceivers and 3rd parties. The unknown SFP from the above example,  actually  works in a  cisco  3835.

 Yes the cisco 3560 switch,   rejected the same  SFP ,  but the router was okay with it.  Here's a "show controller gi 0/0" output for that transceiver;

 Notice the FINISAR corp? And part#  FTFL8519P2BNL?

Okay guess what, the cisco brand GLC-SX-MM are also manufactor by the same vender ; FINISAR.

Look here;

and here;

So the same vendor with a cisco brand vrs non-cisco brand. And the non-branded SFP does not,  and let me repeat, " does NOT work in a cisco switch " but works in a router.

Okay you think that's weird, a cisco brand GLC-SFP-T 1000baseT SFP adapter of mine that works in a cisco switch. Does not work in a cisco router. I have numerous cisco TAC case on this  exact issues, and TAC has been mute and speechless with giving me an solid answer; "as to why?".  They have always exchanged or replaced the SFP transceiver, but  you would expect a cisco branded  SFP, would work in a cisco router or switch.

Look here if you doubt me;

Yes, this was from  a cisco brand GLC-T, &  that did not work in a cisco router.

Here's the line up of the 4 SFP that I tested for this blog, one being a 1000baseT and 3 being a GLC-SX-MM fiber. With the top SFP being a cisco badge SFP, you can make it out if you look very close. The only un-labeled cisco SFP works in a router,  but not in a switch.

And lastly, here's a another cisoc SFP that works in a router or switch;

So always remember to check for cisco compatible SFP, &  if you don't buy cisco branded SFPs. And even a branded cisco SFP , might not work across all cisco hardware and linecards and ios versions.

btw: these last examples where done against a cisco 3825 running ioscode;

Ken Felix
Freelance Network & Security Engineer
kfelix -at- hyperfeed --dot-- com

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