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[PTX] FEC corrected errors increasing on link between QSFP-100GBASE-SR4(740-058734) and QSFP-100G-SR4-T2(740-061405)

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Article ID: KB35145 KB Last Updated: 16 Oct 2019Version: 1.0
Summary:

When a direct link between QSFP-100GBASE-SR4(740-058734) and QSFP-100G-SR4-T2(740-061405) is Up with normal Diagnostics Optics Monitoring data (DOM) on both QSFP types, the "FEC Corrected Errors" rate may be seen to be increasing on the interfaces.

This article clarifies that an incrementing "FEC Corrected Errors" rate is normal for a link that is running Forward Error Correction (FEC) because it indicates that the errored bits have been corrected by FEC already.

Symptoms:

An experimental test result is shown as follows. FEC91 is RS-FEC, which is compliant with IEEE 802.3-2015 Clause 91.

Test Topology

 
 FPC 10 : FPC3-SFF-PTX-1X
  PIC 0 : 10x100/10x40/40x10GE

Xcvr 0 QSFP-100G-SR4-T2 (740-061405) ------ MMF ------ Xcvr 1 QSFP-100GBASE-SR4 (740-058734)
Xcvr 2 QSFP-100G-SR4-T2 (740-061405) ------ MMF ------ Xcvr 3 QSFP-100GBASE-SR4 (740-058734) 
 

The following outputs show the FEC supporting hardware and highlight the incrementing FEC Corrected Errors rate counter. 

User@ptx3000> show chassis hardware
Hardware inventory:
Item             Version  Part number  Serial number     Description
Chassis                                JN1260BC8AJC      PTX3000
Midplane         REV 27   750-044645   ACPG6953          Backplane
FPM              REV 02   760-059087   ACNX8519          Front Panel Display
PSM 0            REV 06   740-044981   1EDK5161015       AC 12V Power Supply
PSM 1            REV 06   740-044981   1EDK5161026       AC 12V Power Supply
PSM 2            REV 06   740-044981   1EDK5161030       AC 12V Power Supply
PSM 3            REV 06   740-044981   1EDK5040298       AC 12V Power Supply
Routing Engine 0 REV 12   740-026942   P737A-006333      RE-DUO-2600
Routing Engine 1 REV 12   740-026942   P737A-006300      RE-DUO-2600
CB 0             REV 06   750-058864   ACPN2836          Control Board
CB 1             REV 06   750-058864   ACPN2840          Control Board
FPC 10           REV 40   750-057064   ACPJ9207          FPC3-SFF-PTX-1X
  CPU                     BUILTIN      BUILTIN           SMPC PMB
  PIC 0          REV 06   750-070203   BCAJ3689          10x100/10x40/40x10GE
    Xcvr 0       REV 01   740-061405   1ECQ11150LC       QSFP-100G-SR4-T2
    Xcvr 1       REV 01   740-058734   1ACQ111401P       QSFP-100GBASE-SR4
    Xcvr 2       REV 01   740-061405   1ECQ11150H1       QSFP-100G-SR4-T2
    Xcvr 3       REV 01   740-058734   1ACQ11460EN       QSFP-100GBASE-SR4

User@ptx3000> show chassis pic fpc-slot 10 pic-slot 0
FPC slot 10, PIC slot 0 information:
  Type                             10x100/10x40/40x10GE
  State                            Online
  PIC version                  1.6
  Uptime                         7 minutes, 55 seconds

PIC port information:
                         Fiber                    Xcvr vendor       Wave-    Xcvr         JNPR
  Port Cable type        type  Xcvr vendor        part number       length   Firmware     Rev
  0    100GBASE SR4      MM    JUNIPER-AVAGO      AFBR-89CDDZ-JU1   850 nm   0.0          REV 01
  1    100GBASE SR4      MM    JUNIPER-FINISAR    FTLC9551REPM-J3   850 nm   0.0          REV 01
  2    100GBASE SR4      MM    JUNIPER-AVAGO      AFBR-89CDDZ-JU1   850 nm   0.0          REV 01
  3    100GBASE SR4      MM    JUNIPER-FINISAR    FTLC9551REPM-J3   850 nm   0.0          REV 01

User@ptx3000> show interfaces et-10/0/0 extensive
Physical interface: et-10/0/0, Enabled, Physical link is Up
  Interface index: 129, SNMP ifIndex: 504, Generation: 132
  Link-level type: Ethernet, MTU: 1514, Speed: 100Gbps, BPDU Error: None,
  Loop Detect PDU Error: None, Loopback: Disabled, Source filtering: Disabled,
  Flow control: Enabled
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Link flags     : None
  CoS queues     : 8 supported, 8 maximum usable queues
  Hold-times     : Up 0 ms, Down 0 ms
  Damping        : half-life: 0 sec, max-suppress: 0 sec, reuse: 0, suppress: 0, state: unsuppressed
  Current address: 08:b2:58:66:d3:a7, Hardware address: 08:b2:58:66:d3:a7
  Last flapped   : 2019-09-18 08:36:29 IST (00:12:49 ago)
  Statistics last cleared: Never
  Traffic statistics:
   Input  bytes  :                    0                    0 bps
   Output bytes  :                    0                    0 bps
   Input  packets:                    0                    0 pps
   Output packets:                    0                    0 pps
   IPv6 transit statistics:
   Input  bytes  :                    0
   Output bytes  :                    0
   Input  packets:                    0
   Output packets:                    0
  Input errors:
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0, L3 incompletes: 0,
    L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0
  Output errors:
    Carrier transitions: 1, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0,
    HS link CRC errors: 0, MTU errors: 0, Resource errors: 0
  Egress queues: 8 supported, 4 in use
  Queue counters:       Queued packets  Transmitted packets      Dropped packets
    0                                0                    0                    0
    1                                0                    0                    0
    2                                0                    0                    0
    3                                0                    0                    0
  Queue number:         Mapped forwarding classes
    0                   best-effort
    1                   expedited-forwarding
    2                   assured-forwarding
    3                   network-control
  Active alarms  : None
  Active defects : None
  PCS statistics                      Seconds
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC Mode  :                  FEC91
  Ethernet FEC statistics              Errors
    FEC Corrected Errors                    0
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate               0
    FEC Uncorrected Errors Rate             0

User@ptx3000> show interfaces et-10/0/1 extensive
Physical interface: et-10/0/1, Enabled, Physical link is Up
  Interface index: 130, SNMP ifIndex: 505, Generation: 133
  Link-level type: Ethernet, MTU: 1514, Speed: 100Gbps, BPDU Error: None,
  Loop Detect PDU Error: None, Loopback: Disabled, Source filtering: Disabled,
  Flow control: Enabled
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Link flags     : None
  CoS queues     : 8 supported, 8 maximum usable queues
  Hold-times     : Up 0 ms, Down 0 ms
  Damping        : half-life: 0 sec, max-suppress: 0 sec, reuse: 0, suppress: 0, state: unsuppressed
  Current address: 08:b2:58:66:d3:ab, Hardware address: 08:b2:58:66:d3:ab
  Last flapped   : 2019-09-18 08:36:28 IST (00:12:55 ago)
  Statistics last cleared: Never
  Traffic statistics:
   Input  bytes  :                    0                    0 bps
   Output bytes  :                    0                    0 bps
   Input  packets:                    0                    0 pps
   Output packets:                    0                    0 pps
   IPv6 transit statistics:
   Input  bytes  :                    0
   Output bytes  :                    0
   Input  packets:                    0
   Output packets:                    0
  Input errors:
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0, L3 incompletes: 0,
    L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0
  Output errors:
    Carrier transitions: 1, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0,
    HS link CRC errors: 0, MTU errors: 0, Resource errors: 0
  Egress queues: 8 supported, 4 in use
  Queue counters:       Queued packets  Transmitted packets      Dropped packets
    0                                0                    0                    0
    1                                0                    0                    0
    2                                0                    0                    0
    3                                0                    0                    0
  Queue number:         Mapped forwarding classes
    0                   best-effort
    1                   expedited-forwarding
    2                   assured-forwarding
    3                   network-control
  Active alarms  : None
  Active defects : None
  PCS statistics                      Seconds
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC Mode  :                  FEC91
  Ethernet FEC statistics              Errors
    FEC Corrected Errors             15583531
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate           21816
    FEC Uncorrected Errors Rate             0

User@ptx3000> show interfaces et-10/0/2 extensive
Physical interface: et-10/0/2, Enabled, Physical link is Up
  Interface index: 131, SNMP ifIndex: 643, Generation: 134
  Link-level type: Ethernet, MTU: 1514, Speed: 100Gbps, BPDU Error: None,
  Loop Detect PDU Error: None, Loopback: Disabled, Source filtering: Disabled,
  Flow control: Enabled
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Link flags     : None
  CoS queues     : 8 supported, 8 maximum usable queues
  Hold-times     : Up 0 ms, Down 0 ms
  Damping        : half-life: 0 sec, max-suppress: 0 sec, reuse: 0, suppress: 0, state: unsuppressed
  Current address: 08:b2:58:66:d3:af, Hardware address: 08:b2:58:66:d3:af
  Last flapped   : 2019-09-18 08:36:28 IST (00:12:59 ago)
  Statistics last cleared: Never
  Traffic statistics:
   Input  bytes  :                    0                    0 bps
   Output bytes  :                    0                    0 bps
   Input  packets:                    0                    0 pps
   Output packets:                    0                    0 pps
   IPv6 transit statistics:
   Input  bytes  :                    0
   Output bytes  :                    0
   Input  packets:                    0
   Output packets:                    0
  Input errors:
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0, L3 incompletes: 0,
    L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0
  Output errors:
    Carrier transitions: 1, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0,
    HS link CRC errors: 0, MTU errors: 0, Resource errors: 0
  Egress queues: 8 supported, 4 in use
  Queue counters:       Queued packets  Transmitted packets      Dropped packets
    0                                0                    0                    0
    1                                0                    0                    0
    2                                0                    0                    0
    3                                0                    0                    0
  Queue number:         Mapped forwarding classes
    0                   best-effort
    1                   expedited-forwarding
    2                   assured-forwarding
    3                   network-control
  Active alarms  : None
  Active defects : None
  PCS statistics                      Seconds
    Bit errors                           365
    Errored blocks                       365
  Ethernet FEC Mode  :                  FEC91
  Ethernet FEC statistics              Errors
    FEC Corrected Errors           4756489624
    FEC Uncorrected Errors             640004
    FEC Corrected Errors Rate         5832363
    FEC Uncorrected Errors Rate             0

User@ptx3000> show interfaces et-10/0/3 extensive
Physical interface: et-10/0/3, Enabled, Physical link is Up
  Interface index: 132, SNMP ifIndex: 644, Generation: 135
  Link-level type: Ethernet, MTU: 1514, Speed: 100Gbps, BPDU Error: None,
  Loop Detect PDU Error: None, Loopback: Disabled, Source filtering: Disabled,
  Flow control: Enabled
  Device flags   : Present Running
  Interface flags: SNMP-Traps Internal: 0x4000
  Link flags     : None
  CoS queues     : 8 supported, 8 maximum usable queues
  Hold-times     : Up 0 ms, Down 0 ms
  Damping        : half-life: 0 sec, max-suppress: 0 sec, reuse: 0, suppress: 0, state: unsuppressed
  Current address: 08:b2:58:66:d3:b3, Hardware address: 08:b2:58:66:d3:b3
  Last flapped   : 2019-09-18 08:36:28 IST (00:13:04 ago)
  Statistics last cleared: Never
  Traffic statistics:
   Input  bytes  :                    0                    0 bps
   Output bytes  :                    0                    0 bps
   Input  packets:                    0                    0 pps
   Output packets:                    0                    0 pps
   IPv6 transit statistics:
   Input  bytes  :                    0
   Output bytes  :                    0
   Input  packets:                    0
   Output packets:                    0
  Input errors:
    Errors: 0, Drops: 0, Framing errors: 0, Runts: 0, Policed discards: 0, L3 incompletes: 0,
    L2 channel errors: 0, L2 mismatch timeouts: 0, FIFO errors: 0, Resource errors: 0
  Output errors:
    Carrier transitions: 1, Errors: 0, Drops: 0, Collisions: 0, Aged packets: 0, FIFO errors: 0,
    HS link CRC errors: 0, MTU errors: 0, Resource errors: 0
  Egress queues: 8 supported, 4 in use
  Queue counters:       Queued packets  Transmitted packets      Dropped packets
    0                                0                    0                    0
    1                                0                    0                    0
    2                                0                    0                    0
    3                                0                    0                    0
  Queue number:         Mapped forwarding classes
    0                   best-effort
    1                   expedited-forwarding
    2                   assured-forwarding
    3                   network-control
  Active alarms  : None
  Active defects : None
  PCS statistics                      Seconds
    Bit errors                             0
    Errored blocks                         0
  Ethernet FEC Mode  :                  FEC91
  Ethernet FEC statistics              Errors
    FEC Corrected Errors               348021
    FEC Uncorrected Errors                  0
    FEC Corrected Errors Rate             532
    FEC Uncorrected Errors Rate             0
Cause:

An incrementing FEC Corrected Errors counter is normal for a link that is running FEC. It just indicates that the errored bits have been corrected by FEC.

It should be possible to connect QSFP-100GBASE-SR4 and QSFP-100G-SR4-T2 with each other because connecting any pair of 100G SR4 optics is supported as long as they conform to the 100GBASE-SR4 IEEE 802.3 standard. Therefore, the incrementing FEC Corrected Errors counter might only be indicating an interoperability issue between the optics from Finisar and FIT (FIT used to be Avago) because Juniper uses both vendors for each of the SKUs.

Below are the vendor part numbers that have been shipped for both 100G SR4 SKUs:

QSFP-100G-SR4-T2 (740-061405)
FIT: AFBR-89CDDZ-JU1
Finisar: FTLC9551REPM-J1

QSFP-100GBASE-SR4 (740-058734)
FIT: AFBR-89CDDZ-JU2 
Finisar: FTLC9551REPM-J3

Solution:

FEC Corrected Errors is not a problem because it only indicates a possible vendor interoperability issue between Finisar and FIT. Hence no action is required.

However, if the FEC Uncorrected Errors rate is high, it certainly indicates a problem. If FEC Uncorrected Errors increase, open a Support case for troubleshooting the issue.

Note: If the FEC Uncorrected Errors rate is low (<BER 10^-12), there should not be any real problems as per the IEEE 802.3 standard.

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