Computer Networks (CN) is worth about 8 marks per GATE CS paper, or roughly 8.2% of the 100-mark paper, and it is the steadiest high-weight subject in the paper. We counted every networking question in all 23 official GATE CS papers from 2014 to 2026: CN averaged 8.2 marks and never fell below 6 or rose above 10. Within it, IPv4 addressing, CIDR and fragmentation have grown the most, to about 2.7 marks per paper since 2021. The 2027 syllabus has also been cut down noticeably, which changes what is worth studying. This guide covers what changed, topic-by-topic numbers, five worked questions from past papers and a study order.
How we counted: we classified all 1,495 GATE CS questions from 2014 to 2026 by subject and topic, using the official papers as reproduced on Success Tracker's GATE CS PYQ archive. A few questions appear twice in the 2015 papers on that archive, and we counted each of those only once. Confirm the syllabus on the official GATE 2027 syllabus page (IIT Madras).
GATE CS 2027 Computer Networks Syllabus (and What Was Removed)
Computer Networks is Section 10 of the official GATE 2027 CS syllabus. The official text reads:
- Principles of layering
- Basics of switching (circuit, packet and virtual circuit) and performance metrics
- Data link layer: error detection, Medium Access Control, Ethernet
- Distance vector and link state routing
- IPv4: fragmentation, CIDR notation, Network Address Translation
- TCP: flow control and congestion control, socket API
- DNS and HTTP
The GATE 2026 CS syllabus was longer. Comparing the two texts:
- No longer named in 2027: the OSI and TCP/IP stacks as named models (now "principles of layering"), framing, Ethernet bridging, shortest-path and flooding routing, IP support protocols (ARP, DHCP, ICMP), UDP, and SMTP, FTP and Email.
- Newly named: "performance metrics" alongside switching. That covers delay, throughput and bandwidth–delay calculations.
- Unchanged in substance: error detection, MAC and Ethernet, distance vector and link state routing, IPv4 fragmentation, CIDR and NAT, TCP flow and congestion control, sockets, and DNS and HTTP.
This matters because the 2025 and 2026 papers still asked about ARP and DHCP, and older papers asked about network security (digital signatures and encryption, 7 questions in total), which is not listed. Prioritise what the 2027 text names. For the full CS syllabus, see our GATE CS syllabus page.
How Many Marks Does CN Carry in GATE CS?
The official question paper pattern fixes marks only for General Aptitude (15) and Engineering Mathematics (13). This is what CN carried in each paper:
| Year | Marks per paper (set-wise) | % of the 100-mark paper | Questions |
|---|---|---|---|
| 2014 | 9 / 9 / 9 | 9% / 9% / 9% | 6 / 6 / 6 |
| 2015 | 6 / 9 / 9 | 6% / 9% / 9% | 4 / 6 / 6 |
| 2016 | 10 / 9 | 10% / 9% | 6 / 6 |
| 2017 | 8 / 7 | 8% / 7% | 5 / 5 |
| 2018 | 7 | 7% | 5 |
| 2019 | 9 | 9% | 5 |
| 2020 | 6 | 6% | 4 |
| 2021 | 9 / 7 | 9% / 7% | 5 / 4 |
| 2022 | 10 | 10% | 6 |
| 2023 | 8 | 8% | 5 |
| 2024 | 9 / 9 | 9% / 9% | 6 / 6 |
| 2025 | 6 / 6 | 6% / 6% | 4 / 5 |
| 2026 | 8 / 9 | 8% / 9% | 5 / 6 |
| Average (23 papers) | 8.2 | 8.2% (range 6–10%) | 5.3 |
What this means: CN is the most predictable high-weight subject. It averaged 8.2 marks both before and after 2021, with a narrow 6 to 10 range. With about 5 questions per paper, it rewards broad coverage of the syllabus over deep specialisation. For how CN compares with other subjects, see our GATE CSE subject-wise weightage analysis.
Topic-Wise Weightage: Where CN Marks Come From
We grouped the 122 CN questions by layer, with the average marks per paper across all 23 papers:
| Topic | Questions | Total marks | Avg marks per paper (23 papers) | Last asked |
|---|---|---|---|---|
| IPv4 addressing, CIDR and fragmentation | 31 | 49 | 2.1 | 2026 |
| Data link: error detection and sliding window | 20 | 36 | 1.6 | 2026 |
| TCP: flow control, congestion control and handshake | 21 | 30 | 1.3 | 2026 |
| Application layer: DNS, HTTP (and security, now removed) | 20 | 25 | 1.1 | 2026 |
| MAC protocols and Ethernet | 12 | 20 | 0.9 | 2025 |
| Routing (distance vector, link state) | 10 | 15 | 0.7 | 2025 |
| Layering, switching and performance | 8 | 13 | 0.6 | 2026 |
Looking at individual topics, the most-asked across all 23 papers were IPv4 fragmentation (14 questions, 21 marks), sliding window and link efficiency (10 questions, 18 marks), subnetting and CIDR (7 questions, 12 marks) and TCP congestion control (6 questions, 11 marks).
Three patterns stand out:
- The network layer leads and keeps growing. IPv4 addressing, CIDR and fragmentation rose from about 1.7 to 2.7 marks per paper. Fragmentation counts, usable host counts and address-block allocation are almost guaranteed every year.
- TCP is rising. It went from 1.1 to 1.6 marks per paper. Congestion control (slow start, thresholds, rounds to reach congestion avoidance) and the 3-way handshake are the most common forms.
- The application layer has shrunk, from 1.5 to 0.5 marks per paper, and the 2027 syllabus narrows it to DNS and HTTP. Security questions (signatures and encryption) were common before 2021 but are no longer in the syllabus.
Question Types in CN
From 2021 to 2026, the 52 CN questions split into 22 MCQs, 15 MSQs and 15 NATs, carrying 31, 22 and 28 marks respectively. About a third of the marks come from numerical answers (fragment counts, window sizes, host counts), and the rest test definitions and protocol behaviour. A wrong 1-mark MCQ costs 1/3 mark and a wrong 2-mark MCQ costs 2/3 mark. NATs and MSQs carry no negative marks (official marking rules). Watch the unit conventions: CN questions often use 1 k = 103 for bandwidth and 1 K = 210 for data sizes, sometimes in the same question.
Topic by Topic: What GATE Asks and How to Prepare
1. IPv4 Addressing, CIDR and Fragmentation
What gets asked: the number of fragments across links with different MTUs, fragment offsets and header fields, usable hosts per subnet, CIDR block allocation, longest-prefix matching, and NAT.
How to prepare: for fragmentation, remember that every fragment except the last must carry a multiple of 8 data bytes, and that each fragment has its own 20-byte header. A router never reassembles fragments, so fragments from the first link get split again on the second (worked example 5). For subnetting, usable hosts = 2host bits − 2. For CIDR allocation, block sizes are powers of two and must align on their own size.
Recent PYQs: ISP block 202.16.0.0/15 (2026, MSQ), fragmenting a 15000-byte message (2025, NAT), header fields a router changes (2024, MSQ).
2. Data Link Layer: Error Detection and Sliding Window
What gets asked: the CRC remainder for given data and a generator, parity and Hamming distance, link utilisation of stop-and-wait, Go-Back-N and selective repeat, and the minimum window size or sequence-number bits.
How to prepare: for CRC, append (generator length − 1) zeros, then divide using XOR (worked example 2). For sliding window, utilisation = W × Tt ÷ (Tt + 2Tp). Full utilisation needs W ≥ 1 + 2Tp/Tt (worked example 3). For sequence numbers, Go-Back-N needs W ≤ 2k − 1 and selective repeat needs W ≤ 2k−1.
Recent PYQs: designing a link-layer protocol (2026, NAT), stop-and-wait (2025).
3. TCP: Flow Control, Congestion Control and Handshake
What gets asked: congestion window growth under slow start and congestion avoidance, the window after a timeout, rounds to reach a threshold, the states and sequence numbers in the 3-way handshake, and the socket API call order.
How to prepare: tabulate the congestion window round by round. Slow start doubles it each RTT until it reaches the threshold, after which it grows by 1 MSS per RTT, and the sender is also capped by the receiver's window. Learn the socket call order for both sides: server socket–bind–listen–accept, and client socket–connect.
Recent PYQs: congestion window after connection setup (2026), TCP connection statements (2026), 3-way handshake (2025, MSQ).
4. MAC Protocols, Ethernet and Routing
What gets asked: the CSMA/CD minimum frame size, ALOHA throughput, Ethernet frame behaviour, distance vector updates and count-to-infinity, and link state basics.
How to prepare: for CSMA/CD, minimum frame size = 2 × propagation delay × bandwidth. Pure ALOHA peaks at 18.4% throughput and slotted ALOHA at 36.8%. For distance vector routing, practise a few rounds of table updates by hand, including what happens when a link fails.
Recent PYQs: CSMA/CD on a 108 bps segment (2024, NAT), routing protocols matching (2025), distance vector updates (2022, NAT).
5. Application Layer, Layering and Performance
What gets asked: DNS resolution steps, HTTP behaviour (persistent connections, what happens when you click a URL), which layer does what, and transfer-time and delay calculations.
How to prepare: under the 2027 syllabus, focus on DNS and HTTP only, and add the delay and throughput numericals implied by "performance metrics". Total delay = transmission + propagation + queuing + processing. Throughput is limited by the slowest link.
Recent PYQs: HTTP statements (2026, MSQ), transferring a 4-million-byte file (2026), DNS resolution (2022, NAT).
Worked Examples from Official GATE CS Papers
Each answer below matches the official answer key, as reproduced on the linked question page.
Example 1: Usable addresses from a mask (GATE CS 2026 Set 2, Q33, 1 mark, NAT)
Question: a network uses the subnet mask 255.255.240.0. How many addresses can be assigned to interfaces?
Solution: 240 is 11110000, so the mask has 8 + 8 + 4 = 20 network bits and 12 host bits. That gives 212 = 4096 addresses, minus the network and broadcast addresses: 4094. Practise this question.
Example 2: CRC remainder (GATE CS 2026 Set 2, Q43, 2 marks)
Question: the data is 110001011 and the generator is 1001. What remainder is appended?
Solution: append 3 zeros to get 110001011000, then divide by 1001 using XOR (modulo-2 division). The remainder is 100, so 110001011100 is transmitted. Always append generator length − 1 zeros before dividing. Practise this question.
Example 3: Window size for full utilisation (GATE CS 2026 Set 1, Q45, 2 marks)
Question: frames are 1000 bits, the link is 100 kbps and the one-way propagation delay is 100 ms. What is the minimum window size for 100% utilisation?
Solution: Tt = 1000 ÷ 105 = 10 ms. The cycle until the first ACK returns is Tt + 2Tp = 10 + 200 = 210 ms. To keep the link busy, W × 10 ms ≥ 210 ms, so W = 21. The trap answer is 20, which forgets the frame's own transmission time. Practise this question.
Example 4: Header fields a router must change (GATE CS 2024 Set 2, Q32, 1 mark, MSQ)
Question: which IPv4 header fields does every router always modify: source IP address, protocol, TTL or header checksum?
Solution: every router decrements TTL, so it must also recompute the header checksum. The source address and protocol pass through unchanged, except under NAT, which not every router does. The answer is TTL and header checksum. Practise this question.
Example 5: Fragmenting twice (GATE CS 2024 Set 1, Q65, 2 marks, NAT)
Question: a 1420-byte datagram (with a 20-byte header) crosses a link with an MTU of 542 and then one with an MTU of 360. How many fragments reach the receiver?
Solution: there are 1400 data bytes. On link 1, the maximum data per fragment is 522, rounded down to a multiple of 8, which is 520. That gives 520 + 520 + 360. On link 2, the maximum data is 340, rounded down to 336. Each 520 splits into 336 + 184, and 360 splits into 336 + 24. That makes 2 + 2 + 2 = 6 fragments, because routers fragment further but never reassemble. Practise this question.
Study Order and Time Plan
CN takes roughly 4 to 5 weeks at 2 hours a day. Work from the bottom layer up, but give the network and transport layers the most time.
- Layering, switching and performance metrics (3 days): the delay and throughput formulas.
- Data link layer (6 days): CRC, sliding window efficiency, MAC protocols and Ethernet.
- Network layer (8–9 days): IPv4, CIDR, fragmentation, NAT, then distance vector and link state routing.
- Transport layer (5–6 days): the TCP handshake, flow control, congestion control and sockets.
- DNS and HTTP (2 days).
- PYQ sweep (3–4 days): all 122 CN questions from 2014 to 2026 on the GATE CS PYQ archive. Skip the security, SMTP and FTP questions, which are no longer in the syllabus.
For where CN fits among all the subjects, see the GATE CSE 2027 month-by-month study plan.
Best Books for GATE CS Computer Networks
| Book | Use it for |
|---|---|
| Kurose & Ross, Computer Networking: A Top-Down Approach | The primary text: TCP, IP, routing, DNS and HTTP. |
| Tanenbaum, Feamster & Wetherall, Computer Networks (6th ed.) | The data link layer, MAC protocols and error detection. |
| Behrouz Forouzan, Data Communications and Networking | Many numerical examples for fragmentation and subnetting. |
For other subjects, see our best books for GATE CSE 2027. The full course, covering all subjects with lectures and mock tests, is on the GATE CS course page.
Common Mistakes in GATE CN
- Forgetting the 8-byte rule when sizing fragments.
- Assuming routers reassemble fragments. Only the destination does (Example 5).
- Leaving out the frame's own transmission time in window-size calculations (Example 3).
- Counting all 2host bits addresses as usable. Subtract the network and broadcast addresses.
- Mixing 103 and 210 in bandwidth and data-size calculations.
Key Takeaways
- CN averaged 8.2 marks per paper (8.2% of the paper) across 23 official GATE CS papers (2014–2026), always between 6 and 10.
- IPv4 addressing, CIDR and fragmentation is the largest and fastest-growing topic, at about 2.7 marks per paper since 2021.
- TCP congestion control is rising, while the application layer has shrunk to DNS and HTTP.
- The 2027 syllabus no longer names ARP, DHCP, ICMP, UDP, SMTP, FTP, framing or bridging. Prioritise what it does list.
Frequently Asked Questions
How many marks does Computer Networks carry in GATE CS?
The official pattern does not fix marks per CS subject. Across all 23 official GATE CS papers from 2014 to 2026, CN averaged 8.2 marks per paper, which is 8.2% of the 100-mark paper, and always stayed between 6 and 10.
Which CN topics are most important for GATE CS 2027?
IPv4 addressing, CIDR and fragmentation (about 2.7 marks per paper since 2021), the data link layer (error detection and sliding window, about 1.7) and TCP (about 1.6).
Has the Computer Networks syllabus changed for GATE 2027?
Yes. Compared with the 2026 syllabus, the 2027 text no longer names the OSI and TCP/IP stacks, framing, Ethernet bridging, shortest-path and flooding routing, ARP, DHCP, ICMP, UDP, SMTP, FTP or Email. It adds "performance metrics" alongside switching. Error detection, MAC, Ethernet, routing, IPv4, TCP, sockets, and DNS and HTTP remain.
Which book is best for CN for GATE CS?
Kurose and Ross's Computer Networking: A Top-Down Approach covers most of the syllabus. Add Tanenbaum for the data link layer and Forouzan for numerical practice.
Is network security in the GATE CS 2027 syllabus?
No. Digital signatures and encryption appeared in older papers, but the 2027 Computer Networks syllabus does not list security topics.
Where can I practise GATE CS CN PYQs?
Every GATE CS question from 2014 to 2026 is free on Success Tracker's GATE CS PYQ archive, with the official answer and a worked solution.
Next in This Series
- Operating System for GATE CS 2027
- Computer Organization and Architecture for GATE CS 2027
- DBMS for GATE CS 2027
- GATE CSE subject-wise weightage
- GATE CS 2027 complete guide
Sources
- GATE 2027 CS Syllabus (PDF), IIT Madras: Section 10, Computer Networks
- GATE 2026 CS Syllabus (PDF), IIT Guwahati: Section 10 (for the comparison)
- GATE 2027 Question Paper Pattern, IIT Madras: marks distribution and negative marking
- Official GATE CS question papers and answer keys, 2014–2026 (23 papers), as reproduced on Success Tracker. Weightage figures are The ML Hub's own count, done on 25 October 2026.