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Difficulty: MediumUtilizing Command-Line Network Troubleshooting Utilities

A network administrator is troubleshooting an issue where users are unable to access a secure website hosted on an internal Linux server. The administrator executes the command `netstat -an` on the server and receives the following output snippet:

text Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State tcp 0 0 0.0.0.0:80 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN

Based on this output, which of the following is the primary cause of the connectivity failure?

  1. The web server daemon is actively listening for unencrypted HTTP traffic on port 80, but the HTTPS service on port 443 is not running or listening.Answer
  2. B
    The server is receiving secure encrypted traffic on port 22 instead of port 443, causing a protocol mismatch error.
  3. C
    The local DNS resolver on the client workstation failed to query the authoritative server for an AAAA record.
  4. D
    The server's CNAME record is misconfigured, preventing TCP handshake packets from reaching port 80.

Answer

The web server daemon is actively listening for unencrypted HTTP traffic on port 80, but the HTTPS service on port 443 is not running or listening.
The `netstat -an` output displays numerical network addresses and active socket states. The snippet shows TCP port 80 (HTTP) and TCP port 22 (SSH) in the `LISTEN` state. Because secure web traffic uses TCP port 443 (HTTPS), and port 443 does not appear in the active listening socket table, client requests over HTTPS will be refused at the transport layer.

Step-by-Step Solution

1
Analyze the command output
Identify active network socket listeners: TCP port 80 (HTTP) and TCP port 22 (SSH) bound to all IPv4 interfaces (0.0.0.0) in the LISTEN state.
The netstat -an command displays numeric network addresses and port numbers currently bound by local daemons.
2
Evaluate user access requirements against socket states
Users are attempting to connect via secure HTTPS (standard TCP port 443). However, netstat shows no service listening on TCP port 443.
For clients to establish a TCP handshake on port 443, the web server service must have a socket configured in the LISTEN state on that port.
3
Deduce the primary root cause
The web server service is either stopped, misconfigured, or missing a TLS listener binding for TCP port 443.
The absence of port 443 in netstat output directly accounts for the inability to establish secure connections.

Key Concept

Analyzing netstat listening sockets to verify network service availability and port bindings
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Topics

Utilizing Command-Line Network Troubleshooting Utilities

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