To determine where slowness is occurring-especially if an upstream router is suspected-the best tools are ping and tracert/traceroute. Network+ (N10-009) troubleshooting objectives emphasize using these to test connectivity, latency, and the path packets take through the network. Ping measures reachability and round- trip time; rising latency or packet loss can indicate congestion or a failing link/device. Tracert identifies each hop along the route and reports per-hop response times, helping pinpoint whether delays begin at a specific hop (for example, the default gateway, the upstream router, or a provider edge). This allows the engineer to localize the problem area and decide whether the issue is internal, at the upstream router, or beyond.
nslookup and dig are DNS tools; they diagnose name resolution, not general network slowness location.
Nmap focuses on scanning ports/hosts, and a "speed tester" measures throughput but does not locate the failing hop. tcpdump and protocol analyzer can reveal retransmissions, windowing, or application behavior, but they are not the fastest first-choice tools for locating an upstream routing/performance bottleneck across hops. Hence, tracert and ping are the correct pair.