The IIT Madras BS Computer Networks (Computer Networks) End Term paper sat on 10 May 2026, in the January 2026 term: 22 questions for 50 marks in 180 minutes. Every question is below with its answer. Take it as a timed mock test to be marked, or read it through first.
When using Dijkstra’s algorithm to find shortest path in a graph, which of the following statement is not true?
It can find shortest path within the same graph data structure
Every time a new node is visited, we choose the node with smallest known distance/cost (weight) to visit first
Shortest path always passes through least number of vertices
The graph needs to have a non-negative weight on every edge
Correct answer
Shortest path always passes through least number of vertices
The browser establishes a TCP connection with the server, but displays a blank page or keeps loading indefinitely. What is the MOST likely issue?
The server did not call listen()
The HTTP response is missing proper headers (e.g., Content-Type or Content- Length)
The client used IPv6 instead of IPv4
The socket buffer size is too small
Correct answer
The HTTP response is missing proper headers (e.g., Content-Type or Content- Length)
The server successfully receives and prints the HTTP request, but the browser shows “This site can’t be reached” or keeps loading. What is the most likely reason?
The server did not call bind()
The server did not send an HTTP response back to the client
The browser used HTTPS instead of HTTP
The request buffer size was too small
Correct answer
The server did not send an HTTP response back to the client
The server crashes while handling incoming data. The error occurs at:
What is the most likely cause?
recv() returned -1 causing invalid indexing
BUFFER SIZE is too large
The server is not bound to the correct port
The client is using HTTP/2 instead of HTTP/1.1
Correct answer
recv() returned -1 causing invalid indexing
In your parser, you read:
If data offset byte is 0x50, what is the TCP header length? (Assume upper nibble = 5.)
8 bytes
16 bytes
20 bytes
32 bytes
Correct answer
20 bytes
You modify the server to accept a connection and immediately close it after reading a request:
When you open http://127.0.0.1:8080/ in a browser, it shows an error like “Connection reset” or keeps retrying. On the server side, no errors are printed. What is the most likely reason?
The server does not send any HTTP response before closing the connection.
The buffer size is too small to hold the HTTP request.
The browser requires UDP instead of TCP for HTTP.
The server must call write() before read().
Correct answer
The server does not send any HTTP response before closing the connection.
Assume a host in Mumbai wants to send a packet to a server in Delhi, approximately 1600 km away. If the signal travels at 3 × 106 m/s, what is the one-way propagation delay in milliseconds?
NOTE: Assume no processing or queuing delay(in ms).
Correct answer: 533
If the one-way latency between two cities is measured to be 20 ms, the RTT (Round Trip Time) assuming symmetric paths and no processing delay is:
Correct answer: 40
A transmitter sends packets of size 1000 bits at a rate of 5 Mbps from node X to node Y. The one-way delay is observed to vary between 20 ms (no queueing) and 120 ms (maximum queue), with an average of 60 ms. Assume queuing occurs only at one router along the path and there is no packet loss. What is the mean number of packets in the queue at the bottleneck link?
Correct answer: 200
In a circuit-switched network, a source communicates with a destination through 6 intermediate switches. Each switch takes 3 ms to process a reservation request before forwarding it to the next node. The propagation delay between each pair of nodes (i.e., source/switch/destination) is 3 ms. What is the total time (in milliseconds) taken for the reservation request to reach the destination?
Correct answer: 39
Correct answer: 0x2322
A TCP connection uses the following identifiers:
• Source IP = 192.168.1.11 • Destination IP = 10.1.0.5 • Source Port = 55000 • Destination Port = 80
Assuming that TCP port numbers range from 0 to 65535, but 0–1023 are the well-known (privileged) ports and are excluded, how many additional TCP connections can this host theoretically open to the same server (IP 10.0.0.5, port 80) using different source ports?
Correct answer: 64511
A 20 Mbps link has a propagation delay of 400 μs. The transmitter employs the Stop-and-Wait protocol. Assuming each frame is 200 bytes long, what is the maximum data rate possible?
Note: Answer in Mbps
Correct answer: 1.82
In a network with a bottleneck bandwidth of 20 Mbps and a round-trip time of 400 ms,what should be the minimum congestion window size (in bytes) to fully utilize the link?
Correct answer: 1000000
A TCP flow has a congestion window of 60 KB and an RTT of 600 ms. Calculate the average throughput in Mbps. Note: In two point precision
Correct answer: 0.80
In TCP BBR’s bottleneck bandwidth estimation, the ACK arrival rate measured over an epoch gives a delivery rate of 50 Mbps. If the minimum measured RTT (RTTmin) is 200 ms, what is BBR’s current estimate of the bottleneck bandwidth (in Mbps)?
Correct answer: 50
A TCP Reno connection detects congestion when CWND = 200 KB. After triple duplicate ACK, CWND is reduced to 3/4, and additive increase resumes with +1 KB per RTT. Compute the CWND after 3 RTTs post-loss.(in KB)
Correct answer: 153
An ISP manages a network block 172.16.0.0/11. It partitions and assigns a customer a smaller block 172.16.32.0/19.
Determine how many total subnets the ISP could theoretically create from the original /11 block if it subdivides it completely into /19 subnets.
Correct answer: 256
How many distinct prefixes can a /11 block be divided into when it is subnetted up to /18 networks?
Correct answer: 128
An organization has 3,200 devices connected in a private network. Each NAT router can handle up to 80,000 simultaneous connections and can serve 290 devices comfortably. If they use NAT (one public IP per NAT router), how many public IP addresses are required?
Correct answer: 12
Inscript If you are designing sliding window protocol (assume selective repeat) of 8 Mbps which has one way delay of 1.55 seconds. Assuming each frame carries 2kB of data, what is the minimum number of bits you need for the sequence number?
Correct answer: 12
A BBR sender is currently transmitting at a rate of 10 Mbps. During a gain cycle, it applies a gain factor of 1.2 to probe for additional network capacity and then reduces its rate by a factor of 1/1.2 to conserve packets.What are the maximum sending rates of the BBR sender during this gain cycle?
Note:Answer in Mbps
Correct answer: 12
