NetworkingA+

Network Troubleshooting Tools for CompTIA A+ 220-1101

Network troubleshooting tools are essential for diagnosing connectivity problems. CompTIA A+ 220-1101 tests command-line and graphical tools used to diagnose IP configuration, connectivity, name resolution, and network paths. Knowing the right tool for each symptom — and interpreting its output — is a core technician skill tested across both Core 1 and Core 2 exams.

7 min

2 sections · 7 exam key points

1 practice questions

Command-Line Network Tools

ipconfig: displays IP configuration. 'ipconfig' — shows IP, subnet mask, default gateway. 'ipconfig /all' — shows full config including MAC address, DHCP server, DNS servers, lease dates. 'ipconfig /release' — releases DHCP lease. 'ipconfig /renew' — requests new DHCP lease. 'ipconfig /flushdns' — clears local DNS cache (resolves stale DNS records causing wrong site loading).

ping: tests connectivity using ICMP. 'ping 8.8.8.8' — tests internet connectivity by IP. 'ping google.com' — tests DNS AND connectivity. 'ping 127.0.0.1' — tests local TCP/IP stack (should always succeed). 'ping [default gateway IP]' — tests local network connectivity. 'ping -t [IP]' (Windows) — continuous ping. Interpret results: Request timed out = ICMP blocked or host unreachable. Destination host unreachable = no route. TTL expired = routing loop or far destination.

tracert (Windows) / traceroute (Linux): shows the path packets take, hop by hop. Each hop shows the intermediate router IP and round-trip time. Useful for identifying where in the path traffic is failing or slowing down. '*' asterisks: hop is not responding to ICMP (router configured to drop ICMP TTL-expired) — doesn't mean the hop is broken.

nslookup: queries DNS servers. 'nslookup google.com' — resolves name to IP using default DNS server. 'nslookup google.com 8.8.8.8' — queries a specific DNS server. 'nslookup' in interactive mode — type 'server 8.8.8.8' to change DNS, 'set type=MX' for MX records. Useful for comparing results from different DNS servers.

netstat: displays network connections. 'netstat -an' — all connections with numeric addresses. 'netstat -b' — shows which program owns each connection. 'netstat -r' or 'route print' — displays routing table. 'netstat -s' — protocol statistics. Useful for: checking which application is listening on a port, seeing all established connections.

Additional Tools and Physical Tools

net commands: 'net view' — lists computers visible on the network. 'net use' — manage network drive connections. 'net user' — manage local user accounts. 'net start/stop [service]' — start or stop Windows services (e.g., 'net stop spooler' for print spooler).

pathping: Windows tool that combines ping and traceroute. Sends packets to each hop over an extended period and calculates per-hop packet loss statistics. More informative than a single traceroute for identifying intermittent packet loss at a specific hop.

Wi-Fi analyzer: mobile app or software tool that scans wireless networks — shows available SSIDs, signal strength, channel, frequency band. Useful for: identifying channel conflicts, finding strong signal coverage zones, diagnosing poor Wi-Fi signal. Android: Wi-Fi Analyzer app. Windows: built-in (netsh wlan show networks mode=bssid) or third-party apps.

Cable tester: physical tool that verifies continuity, wiring (T568A/T568B), and detects shorts/opens in Ethernet cables. Essential for verifying newly terminated cables. Toner/probe (fox and hound): injects a tone signal on one end of a cable; a probe held near the cable at the other end audibly identifies which cable in a bundle is being traced — essential for cable identification in walls and cable trays.

Key exam facts — A+

ipconfig /all: full config; /release and /renew: DHCP lease management; /flushdns: clears DNS cache
ping 127.0.0.1: tests local TCP/IP stack; ping gateway: tests local network; ping 8.8.8.8: tests internet
tracert: shows path hop by hop; '*' = ICMP blocked, not necessarily broken
nslookup: tests DNS; 'nslookup host DNSserver' queries a specific DNS server
netstat -an: all connections; netstat -b: which program per connection; netstat -r: routing table
pathping: per-hop packet loss statistics over time — more useful than single traceroute
Toner/probe: identifies cables in bundles without labels — tone on one end, probe on other

Common exam traps

If tracert shows '*' for a hop, that hop is down

Many routers are configured to drop ICMP TTL-exceeded messages silently (rate limiting, security policy) — this appears as '*' in traceroute output but the router is still forwarding traffic. As long as subsequent hops appear, traffic is flowing through the silent hop. A true network break shows consecutive '*' entries from the point of failure onward, not a single silent hop in the middle of an otherwise successful trace

Practice questions — Network Tools

These questions are representative of what you will see on A+ exams. The correct answer and explanation are shown immediately below each question.

Q1.A user can access websites by IP address (e.g., 8.8.8.8) but not by name (e.g., google.com). Which command would BEST help diagnose the DNS issue?

A.ping 127.0.0.1

B.tracert 8.8.8.8

C.nslookup google.com

D.netstat -an

Explanation: nslookup directly tests DNS resolution — it queries the configured DNS server and reports whether the name resolves. If nslookup fails, it confirms DNS is the problem and may show whether the DNS server is unreachable or returning wrong results. ping 127.0.0.1 only tests the local stack. tracert 8.8.8.8 tests routing but doesn't test DNS. netstat -an shows existing connections but doesn't test name resolution.

Frequently asked questions — Network Tools

What does 'TTL expired in transit' mean in a ping result?

TTL (Time To Live) is a counter that decrements by 1 at each router hop. When TTL reaches 0, the router discards the packet and sends an ICMP 'TTL expired' message back. In a ping result, 'TTL expired in transit' means the packet ran out of TTL before reaching the destination — either the destination is very many hops away, or there is a routing loop (the packet is circling between routers). Use tracert to visualize the path and identify if a loop exists. Normal internet pings have TTL values of 50–128 at receipt — 'TTL expired' during a ping indicates a routing problem.

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