Monitoring and Performance Quiz
Six questions. Explain each answer in your own words.
A LISTEN socket shows Recv-Q 3 and Send-Q 128. What does this mean?
- A) 3 body bytes received and 128 body bytes sent
- B) 3 connections awaiting accept; maximum accept backlog 128
- C) 3 retransmissions and 128ms RTT
- D) 128 connections currently exist
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Answer: B) 3 connections awaiting accept; maximum accept backlog 128
Explanation: LISTEN queues count connections. Their units differ from stream bytes on ESTABLISHED sockets, so read the state first.
An IP-address curl request has a very small time_namelookup. What can you conclude?
- A) Organizational DNS is always fast
- B) Every DNS cache is empty
- C) This request is unsuitable for validating DNS performance
- D) Server processing took zero time
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Answer: C) This request is unsuitable for validating DNS performance
Explanation: An IP literal does not test lookup of a service name. Also avoid adding cumulative timing fields as independent intervals.
curl succeeds but tcpdump captures nothing. What should you check first?
- A) Selected NIC, filter and capture time window
- B) Reset every host routing table
- C) Enable SSH password login
- D) Increase maximum TCP buffers
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Answer: A) Selected NIC, filter and capture time window
Explanation: A capture depends on observation location and conditions. Align request and capture times and verify the lab NIC selection.
How do 100 Mbit/s and 100 MB/s compare?
- A) They are always equal
- B) The Mbit/s value is eight times larger
- C) They are equal only for HTTP
- D) 100 MB/s represents a rate equivalent to 800 Mbit/s
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Answer: D) 100 MB/s represents a rate equivalent to 800 Mbit/s
Explanation: One byte is eight bits. Comparing real application throughput also requires protocol overhead, observation points and execution conditions.
One Send-Q snapshot is greater than zero. What is the appropriate next action?
- A) Confirm network loss
- B) Double every buffer sysctl
- C) Correlate state, time changes, application progress and packets
- D) Disable the remote firewall
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Answer: C) Correlate state, time changes, application progress and packets
Explanation: Send-Q can include both unacknowledged and unsent bytes. A single snapshot does not establish the cause.
Which distinction between a block I/O scheduler and a network qdisc is correct?
- A) They handle storage requests and network transmit queues respectively
- B) Both are DNS caches
- C) Both validate SSH keys
- D) Both use the same single sysctl
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Answer: A) They handle storage requests and network transmit queues respectively
Explanation: Locate the bottleneck first. Sharing a scheduling concept does not mean they control the same resources or have the same tuning effects.