Network Systems

CCNA1 Module 9: Address Resolution

This is part of the CCNA1 Introduction to Networks course. This page will be updated with texts in the future… for now, please refer to my lecture on my YouTube channel.


ARP Operation – ARP Request

ARP Operation – ARP Reply

ARP Role in Remote Communications

IPv6 Neighbor Discovery

Summary of the Module 9

  • Layer 2 physical addresses (i.e., Ethernet MAC addresses) are used to deliver the data link frame with the encapsulated IP packet from one NIC to another NIC on the same network.
  • If the destination IP address is on the same network, the destination MAC address will be that of the destination device.
  • When the destination IP address (IPv4 or IPv6) is on a remote network, the destination MAC address will be the address of the host default gateway (i.e., the router interface).
  • An IPv4 device uses ARP to determine the destination MAC address of a local device when it knows its IPv4 address.
  • ARP provides two basic functions: resolving IPv4 addresses to MAC addresses and maintaining a table of IPv4 to MAC address mappings.
  • After the ARP reply is received, the device will add the IPv4 address and the corresponding MAC address to its ARP table.
  • For each device, an ARP cache timer removes ARP entries that have not been used for a specified period of time.
  • IPv6 does not use ARP, it uses the ND protocol to resolve MAC addresses.
  • An IPv6 device uses ICMPv6 Neighbor Discovery to determine the destination MAC address of a local device when it knows its IPv6 address.