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Difficulty: HardUtilizing Command-Line Network Troubleshooting Utilities

A network administrator is investigating latency and connectivity issues to an internal database server at 192.168.50.100192.168.50.100. The administrator executes a command-line utility from a client workstation and receives the following output:

Tracing route to 192.168.50.100 over a maximum of 30 hops

0 Workstation1 [10.1.10.15]
1 10.1.10.1
2 10.2.20.1
3 192.168.50.100

Computing statistics for 75 seconds...
Source to Here This Node/Link
Hop RTT Lost/Sent = Pct Lost/Sent = Pct Address
0 Workstation1 [10.1.10.15]
0/ 100 = 0% |
1 1ms 0/ 100 = 0% 0/ 100 = 0% 10.1.10.1
0/ 100 = 0% |
2 15ms 100/ 100 =100% 100/ 100 =100% 10.2.20.1
0/ 100 = 0% |
3 16ms 0/ 100 = 0% 0/ 100 = 0% 192.168.50.100

Which of the following conclusions best explains the results observed in this command output?

  1. The intermediate router at 10.2.20.1 is configured to drop or rate-limit ICMP control traffic, while end-to-end IP reachability to 192.168.50.100 is fully functional.Answer
  2. B
    The local DNS server at 10.2.20.1 is experiencing a failure during reverse name lookup queries for the target destination host.
  3. C
    The destination host at 192.168.50.100 rejected the connection because of a port and protocol mismatch on the listening transport socket.
  4. D
    The host at 192.168.50.100 cannot process IPv4 traffic due to an incorrect AAAA record configuration on the default gateway.

Answer

The intermediate router at 10.2.20.1 is configured to drop or rate-limit ICMP control traffic, while end-to-end IP reachability to 192.168.50.100 is fully functional.
The output reflects a `pathping` report measuring packet loss per hop over a 75-second window. At hop 2 (10.2.20.110.2.20.1), the utility shows 100%100\% packet loss at the node level. However, traffic passing through hop 2 to reach the destination at hop 3 (192.168.50.100192.168.50.100) shows 0%0\% overall packet loss. This behavior confirms that the router at hop 2 is intentionally dropping ICMP control packets (a common security/performance setting known as ICMP rate-limiting) while successfully forwarding actual data traffic to the target host.

Step-by-Step Solution

1
Identify the command-line utility used and its operational behavior.
The command executed is `pathping`, which combines path trace capabilities (`tracert`) with ping statistics collected over an extended sampling interval.
Understanding utility output formatting allows proper distinction between hop-by-hop latency and cumulative loss statistics.
2
Analyze the loss percentages at hop 2 (10.2.20.1) versus hop 3 (192.168.50.100).
Hop 2 reports 100% loss at 'This Node/Link', whereas hop 3 reports 0% overall loss from source to target.
If actual network packet loss occurred at hop 2, packets destined for hop 3 would also be dropped, resulting in equal or higher loss percentages at hop 3.
3
Deduce the root cause of the specific hop 2 anomaly.
The router at 10.2.20.1 deliberately drops direct ICMP Echo Request/Time Exceeded messages directed to its control plane to conserve CPU resources while continuing to forward data plane traffic normally.
Router control plane ICMP rate-limiting is standard behavior and does not affect transit traffic destined for subsequent nodes.

Key Concept

Interpreting pathping and ICMP rate-limiting behavior across intermediate network hops.
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Topics

Utilizing Command-Line Network Troubleshooting Utilities

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