Network utilities: Which protocol is used by the Ping tool to test reachability and measure round trip time between hosts?

Introduction / Context:
Ping is a ubiquitous diagnostic utility used to verify basic IP connectivity and delay. It works by sending special control messages and waiting for replies that indicate a target is reachable at the network layer.

Given Data / Assumptions:

• Ping is not a transport layer application; it tests at the network and control level.
• The tool sends Echo Request messages and expects Echo Reply messages.
• Results include packet loss and round trip time statistics.

Concept / Approach:
Ping uses ICMP, the Internet Control Message Protocol. ICMP Echo Request and Echo Reply message types are used for the probing. ICMP is encapsulated in IP and is distinct from TCP and UDP. ARP and BootP serve other purposes on local networks and bootstrapping.

Step-by-Step Solution:

Verification / Alternative check:
Packet captures show ICMP type 8 (Echo Request) and type 0 (Echo Reply) exchanged during Ping operations.

Why Other Options Are Wrong:

• TCP is a transport protocol used by applications like HTTP, not Ping control messages.
• ARP resolves MAC addresses on local segments but does not measure round trip time across IP networks.
• BootP is for bootstrapping and IP assignment on legacy systems.
• DNS resolves names to IP addresses but is not used for reachability probing.

Common Pitfalls:
Blocking ICMP at firewalls can cause Ping to fail even when hosts are reachable via TCP; assuming Ping tests every aspect of connectivity when it only exercises ICMP and routing.

Final Answer:
ICMP