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Cisco - This interface cannot be modified

On a Cisco switch, I got an error 'This interface cannot be modified' when I tried to access the interface mode. Here's what happened:

The server attached to this particular port on the Cisco switch was frequently being reported offline. The Cisco switch reported that the port was err-disabled and the reason was 'err-disabled link-flap'.

Thinking it would be wise to test the cable, I ran 'test cable-diagnostics prbs start interface te2/0/1'

The 'show cable-diagnostics prbs interface te2/0/1' didnt give much insight into the issue, the output was:

PRBS error counter last cleared: never

Time elapsed since last clear: never

PRBS Max error counters = 65535

Interface   PRBS State   PRBS Error Counter

----------- ------------ -------------------

Te2/0/1     Start        65535

Since this was time sensitive, I decided to replace the cable. Once replaced, the server was still reported as being offline. I thought, probably the interface is disabled and that I would have to manually enable it.

The 'show ip int brie' command reported that the port is administratively down. When I tried to access the interface mode, I got the error 'This interface cannot be modified'. 

I kept thinking, why would the switch stop me from entering the interface configuration mode? 

Since I could not access the interface mode, I thought of checking the current configuration of the port.

I ran 'sho int te2/0/1' and there it was - the reason why I could not access the interface configuration mode.

TenGigabitEthernet2/0/1 is administratively down, line protocol is down (disabled: PRBS running)

Silly me, I had forgotten that the cable test was in progress. I stopped the cable test 'test cable-diagnostics prbs stop interface te2/0/1' & the port was active again.