Network Debugging: Echo, Ping, Traceroute & Client-Server Apps

Question 1

In a TCP echo client-server test, which symptom most strongly suggests the server accepted the connection but never read application data from the socket?

Accepted Answer

The client completes the three-way handshake but blocks waiting for echoed data

Answer

The client immediately receives an ICMP Time Exceeded message

Answer

The client gets a duplicate ARP reply for the server IP

Answer

The client cannot resolve the server's MAC address on the LAN

Question 2

A UDP echo client sends packets to the wrong port on a reachable host. Which outcome is most typical on many systems?

Accepted Answer

The sender may receive an ICMP Port Unreachable message

Answer

The sender always receives a TCP RST segment

Answer

The sender automatically retries with the next higher UDP port

Answer

The sender's socket switches from datagram mode to stream mode

Question 3

When debugging an echo service, what is the main advantage of testing first with loopback address 127.0.0.1?

Accepted Answer

It isolates application and local socket behavior from external network issues

Answer

It verifies DNS delegation for the public hostname

Answer

It bypasses congestion control while keeping packet captures encrypted

Answer

It forces UDP to provide reliable in-order delivery

Question 4

A traceroute output shows the same router IP for three consecutive hops. Which explanation is the most plausible?

Accepted Answer

The path includes a routing loop or repeated traversal through the same device

Answer

Every router after that point is down

Answer

A single router is replying from multiple interfaces with the same source address

Answer

The destination host is sending delayed ACKs for each hop

Question 5

If a ping shows low packet loss but highly variable round-trip times, which issue is most strongly indicated?

Accepted Answer

Jitter caused by queuing or path variability

Answer

A guaranteed DNS cache miss on every probe

Answer

A mismatch between Ethernet and Wi-Fi frame formats

Answer

A permanently closed TCP listening socket

Question 6

In a simple file transfer application over TCP, which bug is most likely if transferred files are consistently truncated only when they exceed a certain size?

Accepted Answer

The client assumes one recv() call returns the entire file payload

Answer

The server forgot to bind to port 80 specifically

Answer

The network path blocks all packets with TTL greater than 64

Answer

The application used newline delimiters in ping requests

Question 7

A chat server appears to 'freeze' only when one connected client becomes slow to receive messages. Which design flaw best explains this?

Accepted Answer

The server uses blocking writes to each client in a single event loop or thread

Answer

The server sends ICMP Echo Requests before every chat message

Answer

The client usernames are stored in DNS TXT records

Answer

The server compares UDP checksums before opening TCP sockets

Question 8

On many Unix-like systems, classic traceroute commonly sends probes with gradually increasing TTL values to discover each hop along the path.

Accepted Answer

True

Answer

False

Question 9

A successful ping to a host proves that a TCP echo service is running and accepting connections on the target machine.

Accepted Answer

False

Answer

True

Question 10

When debugging UDP applications, packet capture is often more important than relying on application logs alone because dropped datagrams may leave no connection-level trace.

Accepted Answer

True

Answer

False

Question 11

In a TCP server, seeing sockets accumulate in TIME_WAIT usually means the application failed to call bind() before listen().

Accepted Answer

False

Answer

True

Question 12

If a file transfer protocol mixes binary file data with line-based control messages on the same TCP stream, poor framing can cause the receiver to misinterpret payload bytes as commands.

Accepted Answer

True

Answer

False

Question 13

A UDP echo test can appear to fail even when the server is healthy if an intermediate firewall silently drops return datagrams.

Accepted Answer

True

Answer

False

Question 14

Which debugging approach is best for confirming whether an application-layer protocol mismatch is causing a client and server to talk past each other?

Accepted Answer

Capture the exchange and compare message framing and byte sequences against the protocol design

Answer

Increase the MTU on both hosts and retry once

Answer

Flush the ARP cache after each packet

Answer

Replace all hostnames with loopback aliases

Question 15

When a traceroute reaches the destination but several intermediate hops show only asterisks, what is the best interpretation?

Accepted Answer

Some routers along the path did not send or permit TTL-expired responses

Answer

The destination forged every missing hop

Answer

The path is invalid because every hop must answer

Answer

The destination switched from IP to a non-routable transport mid-path

Network Debugging: Echo, Ping, Traceroute & Client-Server Apps

Create a competition