By Piyush Wairale (M.Tech, IIT Madras) · Former Instructor, IIT Madras BS Degree Programme · Mentor to 20,000+ GATE aspirants · Updated November 2026

GATE CSE Computer Networks Syllabus 2027 (Official, IIT Madras)

Section 10 of the CS paper: 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.

Full paper structure: GATE CS 2027 syllabus and exam pattern.

Topic-wise Weightage and Priority (GATE CSE Computer Networks)

Layering, Switching and Performance Metrics

Each layer provides a service to the one above and adds its own header (encapsulation). Transmission delay = L/B; propagation delay = d/v; with store-and-forward packet switching across k links, end-to-end delay for one packet is about k × (L/B) + total propagation delay, and pipelining several packets reduces total time. Circuit switching adds setup time but no per-hop store-and-forward delay. Throughput, bandwidth-delay product (B × RTT) and utilisation are the core metrics.

Data Link Layer: Error Detection, MAC and Ethernet

Error detection: parity, checksum and CRC. For CRC with a generator of degree r, append r zeros, divide (XOR) and send the remainder; CRC detects all single-bit errors and all burst errors of length ≤ r. Hamming distance d detects d − 1 errors and corrects ⌊(d − 1)/2⌋.

Flow control at the link: with a = T_p/T_t, stop-and-wait efficiency = 1/(1 + 2a); a sliding window of size W gives efficiency min(1, W/(1 + 2a)). Go-Back-N with k sequence bits allows W ≤ 2^k − 1; Selective Repeat allows W ≤ 2^k−1.

MAC: pure ALOHA max throughput 18.4%, slotted ALOHA 36.8%. For CSMA/CD, minimum frame size = 2 × T_p × bandwidth. Ethernet uses 48-bit MAC addresses and binary exponential backoff.

Distance Vector and Link State Routing

Distance vector (Bellman-Ford style): each router shares its vector with neighbours; D_x(y) = min over neighbours v of (c(x,v) + D_v(y)). Slow to converge and prone to count-to-infinity (mitigated by split horizon and poison reverse). Link state: each router floods its link costs and runs Dijkstra on the full topology; converges faster at the cost of more computation and flooding.

IPv4: Fragmentation, CIDR and NAT

CIDR: a /n block has 2³²⁻ⁿ addresses and 2³²⁻ⁿ − 2 usable hosts. Routers use longest prefix match. Route aggregation merges contiguous, aligned blocks into one shorter prefix.

Fragmentation: data per fragment must be a multiple of 8 bytes and fit in MTU − header. The fragment offset field counts in 8-byte units. Only the last fragment has MF = 0. Reassembly happens only at the destination.

NAT maps many private addresses (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) to one or a few public addresses using port numbers, conserving IPv4 space but breaking end-to-end addressing.

TCP: Flow Control, Congestion Control and the Socket API

TCP is byte-oriented: sequence numbers count bytes, and SYN and FIN each consume one sequence number. Flow control uses the receiver’s advertised window (rwnd). Congestion control: slow start doubles cwnd every RTT until ssthresh, then congestion avoidance adds 1 MSS per RTT. On timeout, ssthresh = cwnd/2 and cwnd = 1 MSS; on 3 duplicate ACKs (fast retransmit/fast recovery in Reno), ssthresh = cwnd/2 and cwnd = ssthresh. The effective send window = min(cwnd, rwnd). Socket API: server calls socket, bind, listen, accept; client calls socket, connect; both then read/write and close.

DNS and HTTP

DNS maps names to IP addresses using a hierarchy (root, TLD, authoritative) via recursive or iterative queries, mostly over UDP port 53. HTTP runs over TCP (port 80). Non-persistent HTTP needs 2 RTTs per object (TCP handshake + request); persistent HTTP reuses the connection, and with pipelining several objects can be fetched in about one RTT after the first.

Five GATE-Style Numericals, Solved (GATE CSE Computer Networks)

Q1 (NAT). How many usable host addresses are in a /26 block?
Solution: 2⁶ − 2 = 62.

Q2 (NAT). A 4000-byte IP datagram (20-byte header) crosses a link with MTU 1500. How many fragments, and what is the offset field of the last one?
Solution: Data = 3980 B. Max data per fragment = 1480 (a multiple of 8). Fragments carry 1480, 1480, 1020: 3 fragments. Last offset = 2960/8 = 370.

Q3 (NAT). Transmission time 1 ms, propagation delay 2 ms. Stop-and-wait efficiency, and the window size for full utilisation?
Solution: a = 2, efficiency = 1/(1 + 4) = 20%; window = 1 + 2a = 5.

Q4 (NAT). CSMA/CD on a 10 Mbps link with a round-trip propagation time of 51.2 µs. Minimum frame size?
Solution: 10⁷ × 51.2 × 10⁻⁶ = 512 bits = 64 bytes.

Q5 (NAT). TCP cwnd is 20 MSS when a timeout occurs. What are the new ssthresh and cwnd, and what is cwnd after 5 more successful RTTs?
Solution: ssthresh = 10, cwnd = 1. Slow start: 2, 4, 8, then capped at 10 (reaching ssthresh), then congestion avoidance gives 11. cwnd after 5 RTTs = 11 MSS.

Common Mistakes to Avoid (GATE CSE Computer Networks)

Forgetting to subtract 2 (network and broadcast) for usable hosts.

Writing the fragment offset in bytes instead of 8-byte units.

Using RTT instead of one-way propagation (or the reverse) in the CSMA/CD and efficiency formulas: read what the question gives.

Letting slow start overshoot ssthresh.

Forgetting SYN and FIN consume sequence numbers in TCP sequence questions.

4-Week Preparation Strategy (GATE CSE Computer Networks)

Week 1: Layering, switching, delays and data link (error detection, sliding window, MAC). Week 2: IPv4, CIDR, subnetting, fragmentation and NAT (50+ numericals). Week 3: Routing, TCP flow and congestion control, sockets, DNS and HTTP. Week 4: 10 years of GATE CS CN questions and the CN tests in the GATE CSE 2027 Test Series, then full-length mocks across all ten subjects.

FAQs: GATE CSE Computer Networks 2027

GATE CSE 2027: All Subject-wise Guides

1. Engineering Mathematics · 2. Digital Logic · 3. Computer Organization & Architecture · 4. Programming & Data Structures · 5. Algorithms · 6. Theory of Computation · 7. Compiler Design · 8. Operating System · 9. Databases (DBMS) · 10. Computer Networks

That completes this GATE CSE Computer Networks guide. Full paper overview: GATE CS 2027 Syllabus, Exam Pattern & Cutoff. Practise all ten subjects in one place with the GATE CSE 2027 Test Series.