The nominal bit rate of CFP in Cisco Nexus 7000 problem


The nominal bit rate in Cisco N7K C7010 problem




1. A brief introduction to CFP interface channels

CFP is a 100G photoelectric conversion product. It hastwo kinds of interface channel, the external 4 * 25G optical channel interfaceand the internal 10 * 10G electrical interface, so the rate of each electricalinterface is 10G.


2. About CFP MSA

In the CFP MSA has defined 800B bytes for the MaximumNetwork Lane Bit Rate, which is the rate of channel optical interface and the800C bytes for the Maximum Host Lane Bit Rate, which is the rate of electricalinterface channel.

This part of MSA is defined as follows:


The unit defined by this byte is 0.2Gbps.

The two are both the CFP’s rate. And the switch deviceis selectively displayed as nominal bitrate, so which rate the device showsdepends on the device and the device software.


3. The coding

Thispart codes in CFP NVR1 800C


There are two pictures above, the first picture is thecorrect code, and the second is to let you see the 800B clearly.

When the 800C is written directly to 33, the rate is(33) H = (51) D, 51 * 0.2G = 10.2G, and the ten electrical interfaces are 100G.And you can also see the 800B is written to 81, (81) H= (129) D, 129*0.2G=25.8G,and the four optical channel interfaces are 100G.



4. On the machineidentification test

Test environment:

Cisco Nexus 7000 N7K-M202CF-22L

Connect via HyperTerminal.


(1) When the 800C bytes in NVR1 are written to 33



the compatibility test is identified as follows:

The actual display is 5.1G.


(2) When the 800C bytes in NVR1 are written to 64, thecompatibility test is identified as follows:


The actual display is 10G.


Result analysis:

In the test, I only changed the 800C, no change to800B. And the nominal bitrate changed proportionally.

For 800C byte:

(33) H= (51) D, 51 * 0.2G = 10.2G,the display should be10.2G,but actually show 5.1G;

(64) H= (100) D, 100 * 0.2G = 20G,the display should be20G,but actually show 10G;

So, the nominal bitrate that the Cisco Nexus 7000 showsis electrical interface’ rate, and it should be 10.2G.

It can be deduced that the unit calculated by the CiscoNexus 7000 N7K-M202CF-22L is different from the CFP MSA or error when itrecognizes the rate. It is used in the calculation of 0.1G instead 0.2G.Thiscan also be proved from Huawei's original CFP code .

As shown in the figure above, Huawei has written 34,(34) H = (52) D, 52 * 0.2G = 10.4G in the definition of CFP NVR1.


5. Summary

CFP module is 10 * 10G internal electrical interfacechannel product, so each channel is 10G bitrate. The nominal bitrate that theCisco Nexus 7000 shows is electrical interface’ rate. The coding definition forthis rate is defined by the 800C bytes of the CFP NVR1 in 0.2G units. And wewrite in the code is 33H, should show 10.2G but the actual display 5.1G. Thisis the problem of Cisco Nexus 7000 N7K-M202CF-22L itself. There is no problemwith our coding and the module itself.

By Faten Fang |Position: FAE


Phone: 15271810438

Date: 2018.02.03

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