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Chapter 7
Troubleshooting Serial Line and Frame Relay Connectivity
The final line of the show interface serial command displays carrier-
specific information:
DCD=up DSR=up DTR=up RTS=up CTS=up
show controllers Command
The show controllers command is used to display interface status and
whether a cable is connected to the interface. Let's look at a couple of
different outputs from the show controllers command.
The first output is from interface serial 0. There is no cable attached
to the interface:
Router_A#show controllers serial 0
HD unit 0, idb = 0x94AEC, driver structure at 0x99870
buffer size 1524 HD unit 0, No cable, clockrate 4000000
cpb = 0x41, eda = 0x4940, cda = 0x4800
RX ring with 16 entries at 0x414800
.
. {some output omitted}
.
TX ring with 2 entries at 0x415000
.
. {some output omitted}
.
0 missed datagrams, 0 overruns
0 bad datagram encapsulations, 0 memory errors
0 transmitter underruns
0 residual bit errors
Router_A#
The second output is from interface serial 1, which does have a cable
connected and is functioning properly:
Router_A#show controllers serial 1
HD unit 1, idb = 0x9D4E0, driver structure at 0xA2260
buffer size 1524 HD unit 1, V.35 DCE cable, clockrate
4000000
cpb = 0x42, eda = 0x3104, cda = 0x3118
RX ring with 16 entries at 0x423000
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