Routing Fundamentals

Reserved IP Address

Below are all the IP address reserved to be private, loopback, link-local or unspecified.

Private IP addresses

  • IPv4 address ranges:
    • -
    • -
    • -
  • IPv6 addresses range - fd00::/8

For these addresses:

  • Cannot be used or routed to the Internet
  • Helps delay IPv4 address exhaustion
  • Used in local area networks (LAN)
  • Provides flexible IP ranges for larger or smaller private networks
  • Allows for additional subnets within the ranges

Loopback IP address

The IP address range/address:

  • (IPv4) -
  • (IPv6) ::1/128

For these addresses:

  • Reserved for a Host's self address (or localhost address)
  • Managed by Operating System
  • Does not utilize the network interface card (NIC)
  • Uses a virtual network interface within the OS
  • Can be used for testing on local machine

The IP address range/address:

  • (IPv4) -
  • (IPv6) fe80::/10

For these addresses:

  • Used in the absence of DHCP or static addresses
  • Can only communicate within its own network segment
  • Routers will not forward packets from a loopback address
  • Uses Address Resolution Protocol (ARP) to ensure that the desired IP address is not in use
  • IPv6 requires a link-local address even if a routable address has been assigned

Unspecified Address

  • (IPv4)
  • (IPv6) ::

Global Networks and Routing

Types of networks:

  • Personal Area Network (PAN): Smallest and simplest network type. Generally consists of one or more people connected through a single device.
  • Local Area Network (LAN): One of the most common network types. Local Area Networks consists of multiple computers and devices that are connected at a single site. These networks facilitate communication between devices and shared resources such as storage.
  • Metropolitan Area Network (MAN): This type of network is spread across a small area or region, such as a city or college campus. A MAN is a much more complex network and can be used to connect multiple LANs. The administration of a MAN may be handled by individuals or a company (ie ISP).
  • Wide Area Network (WAN): A WAN is a network that spans a large geographical area. WANs are used to connect multiple LANs over huge distances - the greatest example is the internet. LANs connect to a WAN via a router, which permits the use of private IP addresses on the LAN and a public-facing address (or addresses) on the WAN. This is all made possible by Network Address Translation (NAT).