Which mechanisms are used to gather RTT metrics?

• A. ICMP echo requests only
• B. ICMP echo requests or replies (PING), UDP, and TCP probes
• C. UDP probes only
• D. TCP probes only

Answer: (B)

RTT metrics are gathered by sending small probes and timing how long they take to return. The most familiar method is ICMP echo requests and replies (PING), which directly measures round-trip time. But networks often filter ICMP, so relying only on ICMP can miss how long real application traffic takes. To get a fuller picture, RTT can be measured using probes over UDP and TCP as well. These protocols reflect delays that end users actually experience with typical services, and they’re often allowed even when ICMP is blocked. By combining ICMP, UDP, and TCP probes, you obtain RTT measurements that cover different paths and filtering conditions, giving a more robust view of latency. The other options are too narrow, using only a single protocol and potentially missing significant delay paths.