Identifying DTE vs. DCE cabling Which Cisco IOS command reveals whether a DTE or DCE cable is connected to Serial0 and shows associated controller information?

Introduction / Context:
In lab environments and some WAN setups, one side of a serial link provides clocking (DCE) while the other is DTE. Determining which side is DCE is essential because the DCE end must be configured with a clock rate for the link to function. Cisco IOS provides controller-level commands to view this hardware-level detail.

Given Data / Assumptions:

• We are working with classic serial interfaces (for example, Serial0).
• We need to know whether the attached cable is DTE or DCE.
• We want a command that surfaces controller information beyond high-level interface status.

Concept / Approach:

The command show controllers serial 0 displays hardware and controller information for the serial interface, including whether the interface detects a DTE or DCE cable. If DCE is present, you typically must set a clock rate on that interface. High-level commands like show interface will not reliably show the cable role.

Step-by-Step Solution:

Verification / Alternative check:

You can also check both ends of the link; only one side should show DCE. On the DCE side, clock rate is required for lab back-to-back cables.

Why Other Options Are Wrong:

• show interface s0 / show interface serial 0: useful for L1/L2 status but not definitive for cable type.
• show serial 0 controllers: invalid syntax for IOS.
• show cable-type serial 0: not an IOS command.

Common Pitfalls:

• Setting clock rate on the DTE side and wondering why the link remains down.
• Relying on interface status alone without controller details.

Final Answer:

show controllers serial 0