What this topic covers
7 subtopics- Fragmentation11
- IPv611
- IPv4 header8
- ARP4
- ICMP4
- NAT4
- DHCP3
- Beginner 15
- Intermediate 15
- Advanced 15
About this topic
Beyond addresses and routing, the network layer has its helpers: ARP finds MAC addresses, DHCP hands out addresses, ICMP reports errors, NAT stretches IPv4 space, and IPv6 replaces it. GATE regularly asks for fragmentation offsets and counts; interviews ask how ping, traceroute and NAT work. Fragmentation answers here were computed (offsets in 8-byte units) and IPv6 forms produced with Python's ipaddress module.
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Sample questions
Try each one first, then open the answer for the explanation and why the other options are wrong.
What does ARP do?
Show answer and explanation
Explanation
The host broadcasts "who has 10.0.0.1?"; the owner replies with its MAC, and the answer is cached in the ARP table.
Why the other options are wrong
- AThat is DHCP.
- BThat is routing.
- CThat is DNS.
A 4000-byte IPv4 datagram (20-byte header, no options) meets a link with MTU 1500. How many fragments are created?
The answer is a number – work it out, then open the solution.
Show answer and explanation
Explanation
3980 bytes of data; each fragment carries at most 1480 bytes (a multiple of 8): 1480 + 1480 + 1020 → 3 fragments.
A 2400-byte datagram (20-byte header) crosses a link with MTU 620. What is the fragment offset field of the last fragment?
The answer is a number – work it out, then open the solution.
Show answer and explanation
Explanation
Each fragment carries 600 data bytes (a multiple of 8): offsets 0, 75, 150, 225; the last carries 2380 − 1800 = 580 bytes.