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25GbE on QFX5200: FEC does not work properly

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  • 1.  25GbE on QFX5200: FEC does not work properly

    Posted 03-18-2020 02:52

    On a QFX5200 we have channelized a 100GbE QSFP+ with Breakout cable into 4x 25GbE. Config is as following:
    set interfaces et-0/0/18:0 native-vlan-id 100
    set interfaces et-0/0/18:0 mtu 9192
    set interfaces et-0/0/18:0 gigether-options fec fec91
    set interfaces et-0/0/18:0 unit 0 family ethernet-switching interface-mode trunk
    set interfaces et-0/0/18:0 unit 0 family ethernet-switching vlan members 100
    ...
    set interfaces et-0/0/18:0 unit 0 family ethernet-switching storm-control STORMCONTROL
    set interfaces et-0/0/18:1 native-vlan-id 100
    set interfaces et-0/0/18:1 mtu 9192
    set interfaces et-0/0/18:1 gigether-options fec fec91
    set interfaces et-0/0/18:1 unit 0 family ethernet-switching interface-mode trunk
    set interfaces et-0/0/18:1 unit 0 family ethernet-switching vlan members 100
    ...
    set interfaces et-0/0/18:1 unit 0 family ethernet-switching storm-control STORMCONTROL
    set interfaces et-0/0/18:2 native-vlan-id 100
    set interfaces et-0/0/18:2 mtu 9192
    set interfaces et-0/0/18:2 gigether-options fec fec91
    set interfaces et-0/0/18:2 unit 0 family ethernet-switching interface-mode trunk
    set interfaces et-0/0/18:2 unit 0 family ethernet-switching vlan members 100
    ...
    set interfaces et-0/0/18:2 unit 0 family ethernet-switching storm-control STORMCONTROL
    set interfaces et-0/0/18:3 native-vlan-id 100
    set interfaces et-0/0/18:3 mtu 9192
    set interfaces et-0/0/18:3 gigether-options fec fec91
    set interfaces et-0/0/18:3 unit 0 family ethernet-switching interface-mode trunk
    set interfaces et-0/0/18:3 unit 0 family ethernet-switching vlan members 100
    ...
    set interfaces et-0/0/18:3 unit 0 family ethernet-switching storm-control STORMCONTROL
    set forwarding-options storm-control-profiles STORMCONTROL all bandwidth-percentage 5
    set forwarding-options storm-control-profiles STORMCONTROL all no-unknown-unicast
    set forwarding-options storm-control-profiles STORMCONTROL all no-multicast

     

    But regarding FEC the output shows a difference:

    show interfaces et-0/0/18:0
    Physical interface: et-0/0/18:0, Enabled, Physical link is Up
    Interface index: 680, SNMP ifIndex: 585
    Link-level type: Ethernet, MTU: 9192, LAN-PHY mode, Speed: 25000mbps, BPDU Error: None, Loop Detect PDU Error: None, Ethernet-Switching Error: None, MAC-REWRITE Error: None,
    Loopback: Disabled, Source filtering: Disabled, Flow control: Disabled, Media type: Fiber
    Device flags : Present Running
    Interface flags: SNMP-Traps Internal: 0x4000
    Link flags : None
    CoS queues : 10 supported, 10 maximum usable queues
    Current address: 2c:21:31:c6:d7:0b, Hardware address: 2c:21:31:c6:d7:0b
    Last flapped : 2020-03-17 08:10:33 CET (01:43:16 ago)
    Input rate : 0 bps (0 pps)
    Output rate : 2184 bps (3 pps)
    Active alarms : None
    Active defects : None
    PCS statistics Seconds
    Bit errors 0
    Errored blocks 0
    Ethernet FEC Mode : FEC74
    Ethernet FEC statistics Errors
    FEC Corrected Errors 0
    FEC Uncorrected Errors 0
    FEC Corrected Errors Rate 0
    FEC Uncorrected Errors Rate 0
    PRBS Statistics : Disabled
    Interface transmit statistics: Disabled

     

    Background
    Within Juniper Tech Note "QFX5200 25GbE Fiber Optic Interface Interoperability Testing" (https://www.juniper.net/documentation/en_US/release-independent/solutions/information-products/pathway-pages/qfx5200-25gbe-interop-tn.pdf) on page 4 is written "...the IEEE 802.3by standard has defined Clause 91 with Reed-Solomon FEC (RS-FEC) for 25Gb Ethernet..." and so we coded "set interfaces et-0/0/18:0 gigether-options fec fec91" but the show interfaces cmd shows "Ethernet FEC Mode : FEC74".
    This might the current default and only valid parm regarding Release note 18.1R1:
    "FEC support for 25-gigabit and 50-gigabit channel speeds (QFX5210 switches)—Starting with Junos OS Release 18.1R1, you can configure forward error correction (FEC) clauses CL74 and CL91 on QFX5210 switches. FEC CL91 can be configured on 100-gigabit interfaces and FEC CL74 can be configured on 25-gigabit and 50-gigabit interfaces. Because the FEC clauses are applied by default on these interfaces, you must disable the FEC clauses if you do not want to apply them."
    FEC74 means Base-R FEC
    FEC91 meens RS-FEC

     

    Question
    Does this behavior reflect the standard 802.3by correctly? We have a connection to a 25GbE OSA7 card (IBM System z) and the log shows an error with Refcode 2E432104 which meens "During Link init of OSA adapter the channel has detected an incorrect FEC (Forward Error Correction) mode. Please check the FEC Mode on your switch port. Correct FEC Mode is RS-FEC (Reed Solomon) specified by the IEEE 25Gbase-SR specification."
    Does anybody has experience with FEC on 25GbE?



  • 2.  RE: 25GbE on QFX5200: FEC does not work properly

     
    Posted 03-18-2020 08:27

    Hello,

     

    To channelize 100G ports in 4 25G ports the syntax is different

     

    set chassis fpc slot-number port port-number channel-speed speed 

     

    From port et-0/0/0 to et-0/0/3 the command is the following

     

    set chassis fpc 0 port 0 channel-speed 25g

     

    From port et-0/0/4 to et-0/0/7 the command is the following

     

    set chassis fpc 0 port 4 channel-speed 25g

     

     

    https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/channel-speed-edit-chassis-qfx-series-els.html

     

    https://www.juniper.net/documentation/en_US/junos/topics/topic-map/switches-interface-port.html

     

     

    Hope this helps,

     

    Randall

     



  • 3.  RE: 25GbE on QFX5200: FEC does not work properly

     
    Posted 03-18-2020 08:37

    Sorry,  I misunderstood your question.

     

    Found this document and the QFX5200 is not listed on the supported platforms.

     

    https://apps.juniper.net/feature-explorer/feature-info.html?fKey=8287&fn=FEC%20support%20for%20100-gigabit%20port%20speeds

     

    According to this page, FEC CL91 clause is applied by default on these interfaces. If you do not want to apply the FEC CL91 clause, you can disable it.

     

     

     

    Regards,

     

    Randall

     



  • 4.  RE: 25GbE on QFX5200: FEC does not work properly

    Posted 03-23-2020 14:50

    There is a PFE vendor  limitation  that, currently FEC74 is only supported in QFX5200 for 25G.

    Though the cli allows us to configure FEC91 by default internally it is set to FEC74. The only option we have now is to set it FEC74 or set to none.

     

    Options in your case is it to check if the peer FEC can be set to auto, so that he detects the switch FEC settings or set the FEC to none.

     

     



  • 5.  RE: 25GbE on QFX5200: FEC does not work properly
    Best Answer

    Posted 04-09-2020 04:13

    I've got an info from outside: QFX5200 used Broadcom Tomahawk ASIC wich is simply not able to handle FEC91, that's all ...