The cisco show controllers command displays full information about the physical interface of a cisco router itself.
Cisco Show Controllers Command helps to indicate the type of serial cable plugged into a serial port.
Typically, there will only be a DTE cable, which then plugs into a type of Data Service Unit (DSU).
For instance the show controller 0 displays the following information below:
Router#sh controllers s 0
HD unit 0, idb = 0x1229E4, driver structure at 0x127E70
buffer size 1524 HD unit 0, V.35 DTE cable
cpb = 0xE2, eda = 0x4140, cda = 0x4000
The show controller S 1 displays the following information on the router
Router#sh controllers s 1
HD unit 1, idb = 0x12C174, driver structure at 0x131600
buffer size 1524 HD unit 1, V.35 DCE cable
cpb = 0xE3, eda = 0x2940, cda = 0x2800
Notice that serial 0 has a DTE cable, whereas the serial 1 connection has a
DCE cable. Serial 1 would have to provide clocking with the clock rate
command. Serial 0 would get its clocking from the DSU.
Meanwhile, it is good to understand that this is the only command that needs to have a space after the command serial.
Router#sh controllers s1
% Invalid input detected at ‘^’ marker.
with this a anyone taking cisco ccna will be able to identify all controllers information in his router.