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Difficulty: HardUtilizing Command-Line Network Troubleshooting Utilities

A network technician is troubleshooting an issue where client machines on the local network cannot access an internal secure web application hosted at `https://app.corp.local`. The technician executes `nslookup app.corp.local` on a client machine, which successfully resolves `app.corp.local` to IP address `10.10.20.15`. The technician then connects remotely to the server at `10.10.20.15` and runs the `netstat -ano` command, obtaining the following output snippet:

Proto Local Address Foreign Address State PID
TCP 10.10.20.15:80 0.0.0.0:0 LISTENING 2044
TCP 10.10.20.15:8080 0.0.0.0:0 LISTENING 3112
UDP 10.10.20.15:53 *:* 1088

Based on the command output and scenario details, which of the following is the primary cause of the connection failure?

  1. The web application service on the server is not bound or listening on TCP port 443.Answer
  2. B
    The DNS server is missing an AAAA record for the host app.corp.local.
  3. C
    The command-line DNS lookup utility failed because it received a non-authoritative response.
  4. D
    The secure web service is misconfigured to use UDP transport instead of TCP transport.

Answer

The web application service on the server is not bound or listening on TCP port 443.
Secure HTTP (HTTPS) communication requires a web server process listening on TCP port 443. The netstat command output indicates that the server at 10.10.20.15 has active listening sockets for TCP port 80 (HTTP), TCP port 8080, and UDP port 53 (DNS), but no service bound to TCP port 443. Consequently, incoming HTTPS connection attempts to HTTPS default port 443 are rejected by the host OS.

Step-by-Step Solution

1
Analyze DNS lookup results
The domain name `app.corp.local` successfully resolves to IPv4 address `10.10.20.15`, confirming DNS name resolution is functioning properly.
Rule out DNS resolution failure as the root cause of the connection error.
2
Analyze netstat output protocol and port bindings
The netstat snippet lists active listening sockets on TCP port 80 (HTTP), TCP port 8080 (alternate HTTP), and UDP port 53 (DNS).
Identify which network services and transport ports are currently active on the destination server.
3
Correlate client request protocol with server listening ports
The client is attempting an HTTPS connection (`https://app.corp.local`), which requires a listening socket on TCP port 443. No process on the server is listening on TCP port 443.
HTTPS operates over TCP port 443 by standard convention; without a service listening on this port, TCP handshake attempts will be refused.

Key Concept

Analyzing Command-Line Utility Output (netstat socket state and port bindings)
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Topics

Utilizing Command-Line Network Troubleshooting Utilities

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