• CCF & DMF Interface Optics Troubleshooting

 
 
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Overview

Aside from the usual Layer 1 troubleshooting thats available, there are a few other steps  that can be taken to identify Layer 1 interface issues.

1. Basic Layer 1 Troubleshooting

Please ensure you’ve completed the following Layer 1 troubleshooting before moving forward. That would include

  1. Reseating the optics
  2. Replacing the optics
  3. Moving the optics to another port on the switch
  4. Cleaning the cables/fiber
  5. Changing the cables
  6. Loopback testing
  7. Ensuring the port speed and optic types are the same

2. HCL Compliant optics

The next step would to check if the optics used are HCL compliant, meaning are these optics certified to work with the DMF/CCF software. You can check with the following cli command. If the optic is non-HCL compliant, there is no guarantee the optic will work as expected or in newer codes following upgrades.

DMF# show debug switch <switch> inventory
   Port        Type          Media  Status Len    Vendor          Model             S/N             HCL
------------- -------------- ------ ------ ----- ---------------- ---------------- ---------------- ---
ethernet1     10GBASE-SR     Fiber               Arista Networks  SFP-10G-SR       zzz99999999     Yes
ethernet2     10GBASE-SR     Fiber               Arista Networks  SFP-10G-SR       zzz99999999     Yes
ethernet3     NONE
ethernet4     NONE
ethernet5     10GBASE-SR     Fiber               Arista Networks  SFP-10G-SR       zzz99999999     Yes
ethernet6     10GBASE-SR     Fiber               Arista Networks  SFP-10G-SR       zzz99999999     Yes

It is also important to be mindful of counterfeit optics as well.

 


3. Dom Levels

Certain optics can also provide a DOM (Digital Optical Monitoring) output. This output checks if the light levels transmitted and received on the optics are within the correct range.

CCF# show switch <switch> interface ethernet33 dom
~~~~~~~~~~~~ Doms ~~~~~~~~~~~~
Module Voltage Temperature
-------|-------|--------------|
SFF8472 3.40V 45.2C (113.3F)

~~~~~~~~~~~~~~~~~~~~~~~~~~~ Channels ~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Bias current Tx power Rx power Rx power oma
-|------------|-----------------|-----------------|------------|
1 8.576mA 0.5970mW -2.24dBm 0.5667mW -2.47dBm unsupported

Not all optics provide DOM output. Optics that provide DOM output are shown in the Hcl as listed below

4. FEC (Forward error-correction) disable/Enable

Forward error-correction is an effective digital signal processing method that improves the bit error rate of communication links by adding redundant information (parity bits) to the data at the transmitter side so the receiver side uses the redundant information to detect and correct errors that may have been introduced in the transmission link.

As shown above, the signal encoding takes place at the transmitter has to be properly decoded by the receiver in order to extract original signal information. FEC is also unidirectional, it does not require a handshake.

For BCF/DMF ethernet, FEC rules are as the following:

  • FEC is not necessary for ethernet 10/100Mb ethernet
  • FEC is optional but not mandatory on 10G ethernet per the industry standard.
  • FEC is mandatory for 100G ethernet for BCF/DMF products

 

With that being said, if a link between BCF/DMF is not coming up with an external host/box, check FEC on the other end. Try enabling and disabling it on the link or  ensure both BCF/DMF switch has FEC enabled if it is a 100G link. If it is a 10G link, ensure they both have FEC disabled or enabled and there is no mismatch.

CCF(config)# switch <switch> 
interface ethernet3 <--- 100G port
forward-error-correction disable

5. Optics pairing

If you are unsure whether the optics is faulty or not, try making a connection between a pair of BCF/DMF switches (With same optics on both ends) and the interface should come up if it is not faulty. Repeat step 3 and check the DOM output power levels to verify as well.

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