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?