System information

Troubleshooting IBM
Book Title
10-232
Physical layer problem Note: On some Cisco platforms, such as the Cisco 7000 running a
recent Cisco IOS release, the output of the show interfaces command
will indicate the state of line signals.
If the router is full-duplex DCE
1
, check for DTR
2
and RTS
3
. If these
signals are not high, proceed to Step 5. If these signals are high, the
interface should be up. If it is not, contact your technical support
representative.
On a Cisco 7000, if the breakout box shows that the DTR and DTS
signals are high but the show interfaces command shows that they are
not, check the router cabling. In particular, make sure that the 60-pin
high-density cable is not plugged in to the router upside-down.
If the router is half-duplex DCE, check for DTR. If DTR is not high,
proceed to Step 5. If DTR is high, the interface should be up. If it is not,
contact your technical support representative.
Note: Half-duplex is not supported on Cisco 7000 series routers.
If the router is full- or half-duplex DTE, check for CD. If CD is not
high, proceed to Step 5. If CD is high, the interface should be up. If it is
not, contact your technical support representative.
Step 5 If the router is full-duplex DCE, make sure the device is configured for
permanent RTS high. If the device does not allow you to configure
permanent RTS, set the signal high by strapping DTR from the device
side to RTS on the router side (see Figure 10-5).
Step 6 If the router is DCE, it is typical to be required to provide clock to the
device. Make sure the clock rate interface configuration command is
present in the router configuration. Use the show running-config
privileged exec command on the router to view the interface
configuration. The following example shows the clock rate information
for interface serial 0.
Physical layer problem Example:
The following example sets the clock rate on the first serial interface to
64000 bits per second:
interface serial 0
clock rate 64000
If the router is DTE, it should get clock from an external device. Make
sure that a device is providing clock properly. Make sure that the
clocking source is the same for all devices.
Possible Problem Solution