Devices

Device Information: PCs

This page explains the PC's properties and functions as implemented by Packet Tracer 3.2.

A PC has one ethernet, one modem, or one wireless port.
The PC may use DHCP to get an assigned IP address, subnet mask, and default gateway from a DHCP server.
A PC keeps an ARP table.

- It associates IP addresses with MAC addresses using an ARP table.
- A PC builds its ARP table by sending ARP requests to find the MAC address of an IP address. The device in question receives the request and sends an ARP reply back with its MAC address. When the PC receives the reply, it adds the entry to the ARP table.
- The ARP process is not visible to the user.

A PC can send layer 3 unicast packets and layer 2 broadcast frames (view flowchart). When it does:

- It checks if the port is a WAN port.
  - If the port is a WAN port, then sends the frame out.
  - If the port is not a WAN port, then checks if the destination MAC is specified.
    - If the destination MAC address is specified, then sends the frame.
    - If the destination MAC address is not specified, then checks if the destination IP is in the same network as the PC.
      - If the destination IP is in the same network as the PC, then looks up the MAC address of the destination IP in the ARP table.
      - If the destination IP is not in the same network as the PC, then checks if this PC has a default gateway.
        - If the PC does not have a default gateway, then drops the packet.
        - If the PC has a default gateway, then looks up the MAC address of the default gateway in the ARP table.
      - If a matching entry is not found in the ARP table, then drops the frame.
      - If a matching entry is found in the ARP table, then sets the frame's destination MAC address to the matching entry's.
      - Sends out the frame.

When a PC receives a packet (view flowchart):

- It checks if the port is a WAN port.
  - If the port is not a WAN port, then checks if the frame's destination MAC address is the broadcast address.
    - If the destination MAC address is the broadcast address, then process the frame.
    - If the destination MAC address is not the broadcast address, then checks if the frame's destination MAC address matches the port's.
      - If the destination MAC address does not match the port's, then drops the frame.
- It checks if the packet's destination IP address matches the PC's.
  - If the destination IP address matches the PC's, then it processes the packet.
  - If they do not match, then drops the packet.