Switching

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?

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

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

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.

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