constant FEC errors juniper mpc10e 400g

[Aaron Gould <aaron1 () gvtc com>]

We recently added MPC10E-15C-MRATE cards to our MX960's to upgrade our core to 400g.  During initial testing of the 400g 
interface (400GBASE-FR4), I see constant FEC errors.  FEC is new to me.  Anyone know why this is occurring?  Shown below, is an 
interface with no traffic, but seeing constant FEC errors.  This is (2) MX960's cabled directly, no dwdm or anything between 
them... just a fiber patch cable.



{master}
me@mx960> clear interfaces statistics et-7/1/4

{master}
me@mx960> show interfaces et-7/1/4 | grep rror | refresh 2
---(refreshed at 2024-04-17 14:18:53 CDT)---
  Link-level type: Ethernet, MTU: 1514, MRU: 1522, Speed: 400Gbps, BPDU Error: None, Loop Detect PDU Error: None, 
Loopback: Disabled, Source filtering: Disabled,
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                    0
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate               0
    FEC Uncorrected Errors Rate             0
---(refreshed at 2024-04-17 14:18:55 CDT)---
  Link-level type: Ethernet, MTU: 1514, MRU: 1522, Speed: 400Gbps, BPDU Error: None, Loop Detect PDU Error: None, 
Loopback: Disabled, Source filtering: Disabled,
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                 4302
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate               8
    FEC Uncorrected Errors Rate             0
---(refreshed at 2024-04-17 14:18:57 CDT)---
  Link-level type: Ethernet, MTU: 1514, MRU: 1522, Speed: 400Gbps, BPDU Error: None, Loop Detect PDU Error: None, 
Loopback: Disabled, Source filtering: Disabled,
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                 8796
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate             146
    FEC Uncorrected Errors Rate             0
---(refreshed at 2024-04-17 14:18:59 CDT)---
  Link-level type: Ethernet, MTU: 1514, MRU: 1522, Speed: 400Gbps, BPDU Error: None, Loop Detect PDU Error: None, 
Loopback: Disabled, Source filtering: Disabled,
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                15582
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate             111
    FEC Uncorrected Errors Rate             0
---(refreshed at 2024-04-17 14:19:01 CDT)---
  Link-level type: Ethernet, MTU: 1514, MRU: 1522, Speed: 400Gbps, BPDU Error: None, Loop Detect PDU Error: None, 
Loopback: Disabled, Source filtering: Disabled,
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                20342
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate             256
    FEC Uncorrected Errors Rate             0

{master}
me@mx960> show interfaces et-7/1/4 | grep "put rate"
  Input rate     : 0 bps (0 pps)
  Output rate    : 0 bps (0 pps)

{master}
me@mx960> show interfaces et-7/1/4
Physical interface: et-7/1/4, Enabled, Physical link is Up
  Interface index: 226, SNMP ifIndex: 800
  Link-level type: Ethernet, MTU: 1514, MRU: 1522, Speed: 400Gbps, BPDU Error: None, Loop Detect PDU Error: None, 
Loopback: Disabled, Source filtering: Disabled,
  Flow control: Enabled
  Pad to minimum frame size: Disabled
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Link flags     : None
  CoS queues     : 8 supported, 8 maximum usable queues
  Schedulers     : 0
  Last flapped   : 2024-04-17 13:55:28 CDT (00:36:19 ago)
  Input rate     : 0 bps (0 pps)
  Output rate    : 0 bps (0 pps)
  Active alarms  : None
  Active defects : None
  PCS statistics                      Seconds
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC Mode  :                 FEC119
  Ethernet FEC statistics              Errors
    FEC Corrected Errors               801787
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate            2054
    FEC Uncorrected Errors Rate             0
  Link Degrade :
    Link Monitoring                   :  Disable
  Interface transmit statistics: Disabled

  Logical interface et-7/1/4.0 (Index 420) (SNMP ifIndex 815)
    Flags: Up SNMP-Traps 0x4004000 Encapsulation: ENET2
    Input packets : 1
    Output packets: 1
    Protocol inet, MTU: 1500
    Max nh cache: 75000, New hold nh limit: 75000, Curr nh cnt: 1, Curr new hold cnt: 0, NH drop cnt: 0
      Flags: Sendbcast-pkt-to-re
      Addresses, Flags: Is-Preferred Is-Primary
        Destination: 10.10.10.76/30, Local: 10.10.10.77, Broadcast: 10.10.10.79

--
-Aaron