When issuing a ping command on a Cisco device, which symbol in the ping output indicates that an echo request was successful?

Introduction / Context:
This question evaluates your familiarity with Cisco ping output symbols, a simple but important skill for quick troubleshooting at the command line. Cisco IOS uses specific characters to indicate success or different types of failure when you ping a destination, and recognizing them helps you understand network behavior at a glance.

Given Data / Assumptions:
- You are running the ping command from a Cisco router or switch.
- The output shows a series of characters, one for each ICMP echo request sent.
- Different characters such as !, ., U, and others represent different results.
- The question asks which symbol specifically indicates a successful ping reply.

Concept / Approach:
When you ping from a Cisco device, the IOS sends multiple ICMP echo requests. For each packet, it prints a single character: an exclamation mark (!) for a successful reply, a period (.) for a timeout (no reply), a U for destination unreachable, and other letters for different ICMP error codes. The exclamation mark is the one you want to see when checking basic connectivity, as a sequence of !!!!! typically indicates that the test was successful for all packets sent.

Step-by-Step Solution:
Step 1: Recall from IOS documentation or lab practice that ping output frequently displays lines such as !!!!! or ..!U. Each character corresponds to one probe.Step 2: Remember that the exclamation mark (!) means the ICMP echo reply was received within the timeout period.Step 3: Recognize that a period (.) indicates a timeout with no reply, which is not successful.Step 4: Note that U usually indicates an ICMP destination unreachable message, again not a success.Step 5: Choose ! as the correct symbol indicating a successful ping.

Verification / Alternative check:
In a lab, ping a reachable IP address from a Cisco router. You will see output like Sending 5, 100-byte ICMP Echos: !!!!!. This confirms that each ! represents a successful reply. If you ping an unreachable address, you will see sequences with . or U, indicating the failure to receive a proper echo reply.

Why Other Options Are Wrong:
The period (.) is explicitly documented as a timeout indicator, not a success. The question mark (?) is not used as a standard ping result symbol in Cisco IOS; it is more commonly related to help prompts in command line editing. U indicates destination unreachable, which is a failure. F is not a standard ping output code for success in IOS and is included only as a distractor.

Common Pitfalls:
Some learners focus only on whether ping shows 0% or 100% success and do not pay attention to the per-packet symbols, which can provide more detail. Another mistake is to confuse . as meaning “OK” and ! as some form of warning, because exclamation marks often signal alerts in other contexts. In Cisco ping output, however, ! is good news. Remembering this detail speeds up CLI troubleshooting.

Final Answer:
On a Cisco device, the ! symbol indicates that a ping echo request was successful.