Re: constant FEC errors juniper mpc10e 400g

[Schylar Utley <sutley () ozarksgo net>]

FEC on 400G is required and expected. As long as it is “corrected”, you have nothing to worry about. We had the same 
realisation recenty when upgrading to 400G.

-Schylar

From: NANOG <nanog-bounces+sutley=ozarksgo.net () nanog org> on behalf of Aaron Gould <aaron1 () gvtc com>
Date: Wednesday, April 17, 2024 at 2:38 PM
To: nanog () nanog org <nanog () nanog org>
Subject: constant FEC errors juniper mpc10e 400g

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