---
title: "Functions of network layer"
subject: "Computer Networks and Security"
chapter: 4
key: "semester_7/computer_networks_and_security:network-layer-functions"
source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/network-layer-functions
site: BCT Engineering
---

# Functions of network layer

Computer Networks and Security · Chapter 4: Network Layer

- Asked in: 2072 Kartik, 2 marks
- Video: [Lec-41: Network Layer | Responsibilities of Network Layer | OSI Model | Computer Networks](https://www.youtube.com/watch?v=rW1jPlYgp_0) — Gate Smashers
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/network-layer-functions
- Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-4

## Question

What are the functions of the network layer?

## Short answer

The network layer provides logical addressing, routing, packet forwarding, fragmentation/reassembly, internetworking, congestion control, and error reporting via ICMP. It moves packets across multiple networks from source to destination host.

## Answer

The network layer moves packets from the source host to the destination host across one or more networks. Its functions are:

1. **Logical addressing:** gives every host a unique IP address (network part + host part).
2. **Routing:** selects the best path through the network using routing tables and routing protocols (RIP, OSPF, BGP).
3. **Packet forwarding:** receives a packet on one interface and sends it out on the correct interface towards the destination.
4. **Fragmentation and reassembly:** breaks packets that exceed the link MTU into smaller fragments and reassembles them at the destination.
5. **Internetworking:** joins different physical networks into one logical network.
6. **Congestion control:** avoids too many packets in the subnet.
7. **Error reporting and diagnostics:** ICMP reports unreachable destinations and expired TTL.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does fragmentation do?
   A. Joins networks
   B. Breaks packets exceeding the link MTU and reassembles at destination
   C. Adds MAC
   D. Encrypts
   Answer: B. This handles differing MTUs. (Key point: Fragmentation)

2. What is packet forwarding?
   A. Building tables
   B. Receiving a packet on one interface and sending out the correct one
   C. Naming
   D. Checking CRC
   Answer: B. Routing selects paths; forwarding moves packets. (Key point: Forwarding vs routing)

3. What does ICMP provide?
   A. Addressing
   B. Error reporting like unreachable destinations and TTL expiry
   C. Routing
   D. Framing
   Answer: B. ICMP is network-layer error reporting. (Key point: ICMP)

## Related in Computer Networks and Security

- [Functions of data link layer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Adll-functions) — Computer Networks and Security, chapter 3, asked 3×
- [Why network layer is key layer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Anetwork-layer-key-layer) — Computer Networks and Security, chapter 4
- [Functions of physical layer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aphysical-layer-functions) — Computer Networks and Security, chapter 2

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