A computer has to send a packet to a destination host in the same LAN. How will the packet be sent?

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A computer has to send a packet to a destination host in the same LAN. How will the packet be sent?

  • The packet will be sent to the default gateway first, and then, depending on the response from the gateway, it may be sent to the destination host.
  • The packet will be sent directly to the destination host.
  • The packet will first be sent to the default gateway, and then from the default gateway it will be sent directly to the destination host.
  • The packet will be sent only to the default gateway.

For more Questions and Answers:

CCNA 1 – 8.6.2 Module Quiz – Network Layer Answers

The Correct Answer: The packet will be sent directly to the destination host.

Introduction

In networking, understanding how data travels across the network is fundamental to grasping how local area networks (LANs) and internet communication work. When a computer needs to send a packet to another device, it relies on network protocols and address resolutions to determine the most efficient path. One of the most common scenarios is communication within the same LAN — and this scenario does not involve a default gateway.

What is a LAN?

A Local Area Network (LAN) is a network that connects computers within a limited area such as a home, school, office building, or data center. Devices within the same LAN are typically on the same subnet and share the same network address portion of their IP addresses. For example, in the network 192.168.1.0/24, all devices from 192.168.1.1 to 192.168.1.254 are considered in the same LAN.

IP Addresses and Subnets

Every device on a LAN is assigned a unique IP address. The IP address is split into two parts:

  • Network portion: Identifies the subnet.

  • Host portion: Identifies the specific device on that subnet.

When a device needs to send data to another device, it compares its own IP address with the destination IP address. If the network portions match, the destination is on the same LAN.

The Role of the ARP (Address Resolution Protocol)

When a computer wants to send a packet to another computer on the same LAN, it uses ARP to find the MAC address of the destination device. Here’s how it works:

  1. Check the IP address: The computer determines that the destination IP is in the same subnet.

  2. ARP Request: It sends a broadcast ARP request: “Who has IP 192.168.1.5?”

  3. ARP Reply: The target device responds with its MAC address.

  4. Packet Sent: The computer now encapsulates the IP packet in an Ethernet frame addressed to the destination MAC and sends it directly on the LAN.

No routing or gateway is needed because both devices are on the same local network.

When Is the Default Gateway Used?

A default gateway (usually a router) is only used when the destination IP address is outside the sender’s local subnet. In that case:

  • The sender sends the packet to the gateway’s MAC address.

  • The gateway routes the packet toward the external network or internet.

However, for communication inside the same LAN, the gateway is completely bypassed.

Examples

Let’s consider two computers in a LAN:

  • Computer A: 192.168.10.2/24

  • Computer B: 192.168.10.5/24

  • Default Gateway: 192.168.10.1

If Computer A wants to communicate with Computer B:

  1. It checks: Are 192.168.10.2 and 192.168.10.5 on the same subnet?

    • Yes — same /24 subnet.

  2. It sends an ARP request to find the MAC of 192.168.10.5.

  3. It receives the MAC address.

  4. It sends the packet directly to Computer B.

The gateway is not involved at all.

Why This Matters

Understanding this behavior is important for:

  • Troubleshooting networks: Knowing when a gateway should or shouldn’t be involved helps isolate problems.

  • Network design: Ensures efficient use of network resources.

  • Security: Helps in configuring firewalls and access control within LANs.

  • Performance: Direct communication within LANs is faster because it avoids the routing overhead.

Clarifying the Incorrect Options

Let’s review why the other options are incorrect:

  1. “The packet will be sent to the default gateway first, and then, depending on the response from the gateway, it may be sent to the destination host.”

    • ❌ Incorrect: The gateway is not consulted at all for same-subnet communication.

  2. “The packet will first be sent to the default gateway, and then from the default gateway it will be sent directly to the destination host.”

    • ❌ Incorrect: This is how communication happens across different networks — not within the same LAN.

  3. “The packet will be sent only to the default gateway.”

    • ❌ Incorrect: Again, the gateway is irrelevant for communication between devices on the same subnet.

Summary

When a computer sends a packet to another device on the same LAN, the process is handled completely at the data link (Layer 2) and network (Layer 3) levels within the local network. The key steps involve checking the IP address, resolving the MAC address via ARP, and sending the packet directly over the Ethernet network. There’s no need to involve the default gateway.

Thus, the correct answer is:

✅ The packet will be sent directly to the destination host.