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.