GATE CS 2025 Set 1 — Question 40
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Computer Networks → Network Layer: Addressing → Longest Prefix Match
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Question
A packet with the destination IP address arrives at a router whose routing table is shown. Which interface will the packet be forwarded to?
| Subnet Address | Subnet Mask (in CIDR Notation) | Interface |
|---|---|---|
| 145.36.0.0 | /16 | E1 |
| 145.36.128.0 | /17 | E2 |
| 145.36.64.0 | /18 | E3 |
| 145.36.255.0 | /24 | E4 |
| Default | -- | E5 |
Correct answer
(A) E3
Solution
1.Destination IP: . The first two octets are . The third octet is ( in binary).
2.Check Matches:
- E1 (): Mask is . Network part is . Match.
- E2 (): Mask is . Third octet mask is . . Resulting subnet is . No match with .
- E3 (): Mask is . Third octet mask is . . Resulting subnet is . Match.
- E4 (): Mask is . Third octet must be . No match.
4.Conclusion: The packet is forwarded to interface E3.
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