Issue Description: et-9/0/3 interface flapping with hold down timer 500, 1000 ms & sometimes 2000 ms also.

Media is involved between both devices & As per customer, media has been verified and no issue is observed.

set interfaces et-9/0/3 mtu 9192

set interfaces et-9/0/3 hold-time up 0

set interfaces et-9/0/3 hold-time down 4000

set interfaces et-9/0/3 unit 0 bandwidth 51200000000

Customer was flapping the interface with tester.

Hence we followed below POA.

• Set hold down timer to 500ms on interface 

• Enable interface debug for FPC9

start shell pfe network fpc9

debug interface 9 7

exit

• Flap with 50ms at tester

• Collect syslogs from pfe for FPC9

start shell pfe network fpc9

show syslog messages

exit

• Disable interface debug for FPC9

start shell pfe network fpc9

undebug interface

exit

Below are the observations for the 2 flaps done from customer's tester, with 50ms duration.

For 1st flap, the down signal came at 13:12:56.618 & clear signal at 13:12:59.058. The log printing may take additional time, as seen from my lab (around 100ms). So even if we deduct the 100ms from this one too, the total time between down/up signal is more than 2 sec 300 ms, which is far beyond 500ms timer & hence interface went down.

For the 2nd flap it is almost 3 sec 700 ms, which is again higher than earlier.

So the router interface itself is getting delayed signal from the flap, which is why interface is flapping with hold down timer value of 500ms.

From this observation, it seems 3 or 4s is the ideal timer for customer scenario, but from lab I can confirm the router/card is correctly handling 50 ms flap within limit.

1st Flap:

[Jan 21 13:12:56.618 LOG: Info] MQSS(0): CHMAC1: Detected Ethernet MAC Local Fault Delta Event for Port 0 (et-9/0/3)

[Jan 21 13:12:56.618 LOG: Info] MQSS(0): CHMAC1: Ethernet PCS Multilane Alignment Not Done Delta Event for Port 0 (et-9/0/3)

[Jan 21 13:12:57.121 LOG: Info] ifp et-9/0/3 ifd_mdown: 11983858030 ms

|

[Jan 21 13:12:59.058 LOG: Info] MQSS(0): CHMAC1: Cleared Ethernet MAC Local Fault Delta Event for Port 0 (et-9/0/3)

[Jan 21 13:12:59.058 LOG: Info] MQSS(0): CHMAC1: Ethernet PCS Multilane Alignment Done Delta Event for Port 0 (et-9/0/3)

2nd Flap:

[Jan 21 13:25:39.325 LOG: Info] MQSS(0): CHMAC1: Detected Ethernet MAC Local Fault Delta Event for Port 0 (et-9/0/3)

[Jan 21 13:25:39.325 LOG: Info] MQSS(0): CHMAC1: Ethernet PCS Multilane Alignment Not Done Delta Event for Port 0 (et-9/0/3)

[Jan 21 13:25:39.828 LOG: Info] ifp et-9/0/3 ifd_mdown: 11984620657 ms

|

[Jan 21 13:25:43.143 LOG: Info] MQSS(0): CHMAC1: Cleared Ethernet MAC Local Fault Delta Event for Port 0 (et-9/0/3)

[Jan 21 13:25:43.144 LOG: Info] MQSS(0): CHMAC1: Ethernet PCS Multilane Alignment Done Delta Event for Port 0 (et-9/0/3)

Below are the logs from my lab, for 50ms flap. The difference between down/up signal is only ~160ms & interface didn’t flap.

[Jan 21 13:19:47.543 LOG: Info] MQSS(0): CMACPCS0: Detected Ethernet MAC Local Fault Delta Event (et-3/0/0)

[Jan 21 13:19:47.543 LOG: Info] MQSS(0): CMACPCS0: Ethernet PCS Multilane Alignment Not Done Delta Event (et-3/0/0)

[Jan 21 13:19:47.543 LOG: Info] MQSS(0): CMACPCS0: Ethernet PCS per lane Block Locked Delta Event (et-3/0/0) - port_block_lock 0xfffe0

[Jan 21 13:19:47.702 LOG: Info] MQSS(0): CMACPCS0: Cleared Ethernet MAC Local Fault Delta Event (et-3/0/0)

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labroot@jtac-mx2008dc-r2003-re0> show interfaces et-3/0/0 | grep flap  

 Last flapped : 2026-01-12 12:50:32 IST (1w2d 06:15 ago)

This is how I did 50ms flap from peer MX204 device pfe.

SMPC0(jtac-mx204-r2051 vty)# test smic 0 1 0 laser off 50