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[QFX] Incorrect CTLE setting leads to FEC corrected and uncorrected errors

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Article ID: KB34352 KB Last Updated: 28 May 2019Version: 2.0
Summary:

CTLE is a parameter for the 100G optic (not applicable for 100G DAC cable). The CTLE value of the 100G optic is based on the lengths of the trace for each front port and the loss.  When the 100G optic is inserted into the Junos device, it will be programmed with a value by Junos software based on the port number.

The CTLE value is measured with a DCA-X, OIF compliance software with normative CTLE using an HCB plugged into the system.

Symptoms:

In the output of 'show interface et-x/x/x extensive' from QFX5200, some of the ports show FEC Corrected Errors and FEC Uncorrected Errors.

There is no fiber issue, optic issue, and the light level is normal for each lane. 

root@test> show interfaces et-0/0/11 extensive 
Physical interface: et-0/0/11, Enabled, Physical link is Up
  Interface index: 658, SNMP ifIndex: 519, Generation: 150
  Link-level type: Ethernet, MTU: 9216, LAN-PHY mode, Speed: 100Gbps, BPDU Error: None, Loop Detect PDU Error: None, MAC-REWRITE Error: None, Loopback: Disabled, Source filtering: Disabled,
  ...........................
  FEC statistics                       Errors
    FEC MODE                            FEC91
    FEC Corrected Errors            233002817
    FEC Uncorrected Errors                  3 
Cause:

Incorrect CTLE setting for the optic is one of the reasons that cause this issue. QFX5200 may not have been able to program the 100G optics with the correct CTLE value and caused the errors.

Solution:

This issue has been fixed with PR1389478 - Link problems might occur with 100G-AOC on QFX series. Junos 15.1X53-D236 and higher has the fix.

With QFX5200, each front port has different lengths of trace and loss, so the system has defined different CTLE values for each front port's CTLE.

Here is the list of CTLE values for each port in QFX5200:

Port          CTLE value
0	7
1	6
2	6
3	6
4	6
5	5
6	6
7	5
8	5
9	5
10	7
11	7
12	6
13	5
14	4
15	3
16	4
17	5
18	6
19	6
20	7
21	6
22	5
23	5
24	5
25	5
26	6
27	5
28	6
29	6
30	7
31	7

Procedure to check if the CTLE value is correct:

start shell
vty fpc0
show qsfp list
test qsfp <index> write 127 3
test qsfp <index> read 234
test qsfp <index> read 235

Example:
root@test> start shell
root@test:~ # vty fpc0
 
TOR platform (1799 Mhz Pentium processor, 383MB memory, 0KB flash)
 
TFXPC0(vty)# show qsfp list
QSFP Toolkit summary:
  wakeup count: 3148779, debug: 0
  thread: 0xbf689200, itable: 0xbf676da8
 
Index  Name        State  
-----  ----        -----  
    1  qsfp-0/0/0  Present
    3  qsfp-0/0/2  Present
    5  qsfp-0/0/1  Present
    6  qsfp-0/0/3  Present
    7  qsfp-0/0/10 Present
    8  qsfp-0/0/11 Present
 
TFXPC0(vty)# test qsfp 7 write 127 3  
TFXPC0(vty)# test qsfp 7 read 234
  234: 77 <-- 77 both means the lane0 and lane 1 with CTLE value 7
TFXPC0(vty)# test qsfp 7 read 235
  235: 77  <-- 77 both means the lane2 and lane 3 with CTLE value 7


Procedure to change the CTLE value of the 100G optics:
Note: Changing the CTLE value will not impact service and it will take affect immediately. 

start shell
vty fpc0
show qsfp list
test qsfp <index> write 127 3
test qsfp <index> write 234 77  <-- This command to set the CTLE of the 100G optics as 7 for both lane0 and lane1 
test qsfp <index> write 235 77  <-- This command to set the CTLE of the 100G optics as 7 for both lane2 and lane2 
 
Example:
root@test> start shell 
root@test:~ # vty fpc0
 
TOR platform (1799 Mhz Pentium processor, 383MB memory, 0KB flash)
 
TFXPC0(vty)# show qsfp list
QSFP Toolkit summary:
  wakeup count: 3148779, debug: 0
  thread: 0xbf689200, itable: 0xbf676da8
 
Index  Name        State  
-----  ----        -----  
    1  qsfp-0/0/0  Present
    3  qsfp-0/0/2  Present
    5  qsfp-0/0/1  Present
    6  qsfp-0/0/3  Present
    7  qsfp-0/0/10 Present
    8  qsfp-0/0/11 Present
 
TFXPC0(vty)# test qsfp 7 write 127 3  
TFXPC0(vty)# test qsfp 7 write 234 77
TFXPC0(vty)# test qsfp 7 write 235 77
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