Fc2/y is down (Link failure: NOS received)

Question

Please Help
UCSM : 1.4 (3l)
Storage FC Ports : fc2/1, fc2/3, fc2/5
error : fc2/5
B(nxos)# sh interface fc 2/5
fc2/5 is down (Link failure: NOS received)
from UCSM
fc port 5 on fabric interconnect B oper state:failed, reason:Link failure: NOS received
disable and enable port
error : fc2/5
B(nxos)# sh interface fc 2/5
fc2/5 is down (Link failure or not-connected)
wahtis the root cause problem?
Best regards

Answer 1

Hello,
NOS refers to "No operatioal sequence". Fibre channel has primitive seqences which are used to establish and maintain a link among the devices.
During the initial login phase,
1.Fiber channel switch sends a NOS signal
2.HBA connected to it sends an "OLS (offline sequence) signal.
3.Switch would send  a "Link reset"(LR)
4.HBA responds with a "LRR (link reset response)"
When a NOS received condition is met,
•A signal loss or sync loss condition is detected.
•The port is administratively shut down.
•The port is operationally down.
When the port status is in "link failure or not-connected" state, it means that the physical path is not completely active or no active signals has been sent. Check the cables/SFP's if pluged in properly and check the configuration (port type, speed and vsan settings) for further troubleshooting.