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Extended buffer to buffer credits activation on a cisco MDS 9250i

We have a few MDS 9250i switches, ready to replace a couple of 9222i switches and because of long distance links and the distance between the data centers, we would like to use extended buffer credits. The 9250i switches should be able to supply these credits and yes, we have the enterprise license installed on the switches. But we seem unable to get these buffer credits configured on the E ports.

Does anyone know the steps to actually configure extended B2B credits to a port?

To enable the Extended BB_credits feature, you have to type the following command:

switch(config)# fcrxbbcredit extended enable

When we execute this command on the 9250i, we get the following error:

(error) requested config change not allowed


Does the 9250i support Extended BB_credits?
I know it is in the Enterprise license, but does the 9250i hardware platform actually support the feature?
I know the feature is not supported on the MDS 9124/9134/9148 switches even with the Enterprise license installed.


Ozden Karakok

Dear Merlijn,

Extended BB credit feature is supported only for Cisco Director class MDS switches (MDS 95xx, MDS 97xx) and the feature is not supported on Cisco Fabric switches (MDS 9250i & MDS 91xx).

This was not documented clearly in the configuration guide and data sheets, the information should be updated in NX-OS 6.2(9) and above. Here is the updated version of the configuration guide.

In the datasheet it was mentioned that buffer credits: 64 per port (shared-mode ports) and up to 253 on an individual port (dedicated-mode ports), which you need to shut down ports in the port-group.

I hope this helps and I am sorry for the mistake in the configuration guide.

Thanks and kind regards,


Hi Ozden, thanks for the quick reply.

It is clear now, we have to go for / have to live with the 253 max Buffers per port.

But I do think this is strange because the 9250i is the follow-up of the 9222i which does support this feature.
We are busy replacing the 9222i with 9250i at moment and facing this problem.

One other question:
If we are decreasing the buffers on a port to free up buffers for a LW E-port, do you know what is a save Buffer count for normal SW F-ports?
Is it like 8 or 16 buffers?


Hi Merlijn,


Actually it is written as 253 Buffers max per port, it is practically 250 fcrxbbcredit that you can configure on a dedicated-mode FC port when other 3 FC ports in that port-group are in out-of-service mode. If you would like to use/set one of the FC ports in the port-group as LW E-port, the total of Buffer credits of the port-group can not be more than 252 Buffers. The default BB Credits for 16Gbps FC in dedicated-mode will be 64. You can change the speed of the F ports and change the fcrxbbcredit minimum to 2.


I hope this answers your question.




Hi Ozden,

So 16 BB Credits on a dedicated F-port at 8Gbps, a VNX front-end port for example, should be fine? I assume it is more than enough.




Hi Merlijn,


For 8Gbps the default is 32 BB credits, yes you can lower it to 16BB Credits. It should be enough, you need to observe the BB Credits "transitions of BB credit out of zero state" in the interface stats which will give you an indication. So I would say start with 16BB Credits.