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[ACX] How to bring up 40G links between ACX5448 and QFX5100 due to mismatch of FEC settings

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Article ID: KB34390 KB Last Updated: 28 May 2019Version: 1.0
Summary:

ACX5448 needs to disable FEC (Forward Error Correction) mode to bring up 40G-links with QFX5100 because QFX5100 does not support FEC.

Symptoms:

40G links between ACX5448 and QFX5100 switch stay down even with known good fibers and QSFP modules.

Cause:

By default, ACX5448 40G-QSFP modules use FEC74 mode:


user@ACX5448# run show interfaces et-0/1/0 extensive | match fec 
  Active defects : LINK, LOCAL-FAULT
  Ethernet FEC Mode  :                  FEC74 <-- Default FEC settings.
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                    0
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate               0
    FEC Uncorrected Errors Rate             0


user@ACX5448> show chassis hardware 
Hardware inventory:
Item             Version  Part number       Description
Chassis                                     ACX5448
Midplane         REV 07   650-077913        ACX5448

  MIC 1                                     16x10/25GE 4x40/100GE
    PIC 1                 BUILTIN           16x10/25GE 4x40/100GE
      Xcvr 0     REV 01   740-043308        QSFP+-40G-LR4


But QFX5100 does not support FEC on 1G/10G/40G interfaces, which results in Interface down:

user@QFX5100> show interfaces et-0/0/1 extensive | match "fec mode" | count 
Count: 0 lines <<- Means no FEC settings

{master:0}
user@QFX5100> show chassis hardware 
Hardware inventory:
Item             Version  Part number    Description
Chassis                                  QFX5100-24Q-2P
Pseudo CB 0     
Routing Engine 0          BUILTIN        QFX Routing Engine
FPC 0            REV 06   650-056265     QFX5100-24Q-2P
  CPU                     BUILTIN        FPC CPU
  PIC 0                   BUILTIN        24x 40G-QSFP
    Xcvr 1       REV 01   740-052009     QSFP+-40G-LR4
Solution:

Commit the following configuration to disable FEC mode on ACX5448 side:


user@ACX5448# set interfaces et-0/1/0 gigether-options fec none
user@ACX5448# commit

user@ACX5448# run show interfaces et-0/1/0 | match fec 
  Active defects : None
  Ethernet FEC Mode  :                   NONE <<- FEC mode is disabled now.
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                    0
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate               0
    FEC Uncorrected Errors Rate             0


Then check interface status on ACX5448 and QFX5100 respectively.

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