Q: How to configure asynchronous private line using three cables?
A: Symptom: Eight asynchronous ports of two 2511 routers are used in a military area to configure the asynchronous private line. Without an asynchronous private line Modem, two asynchronous ports are connected directly through cables. The user can provide three cables only, for transmitting the receiving, sending and ground signals. As a result, the line protocol is down.
Cause: All the eight signals should be used for the asynchronous private line by default. When there are only receiving, sending and ground signals, the line protocol is down.
Analysis: Use the Flowcontrol..normal command to screen CTS and RTS signals (relevant to flow control), and use the no..detect dtr-dsr command to screen DCD, DTR and DSR signals. When the two commands are used, the line protocol is up.