Other Reserved IP Address Ranges

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• Class D addresses are used for multicast
  • 224.0.0.0 - 239.255.255.255
• Class E addresses are reserved for experimental use and testing
  • 240.0.0.0 - 255.255.255.255

Loopback Addresses

A loopback address is a special address typically used to check that TCP/IP is correctly installed on the local host.

• part of class A
• 127.0.0.0/8 is reserved
• does not require a physical interface to function
• packet sent to a loopback address is not processed by a network adapter
  • is processed as normal by the hosts TCP/IP stack
• every IP host is configured with a default loopback address
  • typically 127.0.0.1
• some hosts have more than one loopback address
  • E.g., routers
• loopback interfaces can be configured with an address from any suitable IP range
  • just needs to be unique on its network
• host will process a loopback address regardless of the physical interface on which it is received

Info

• most hosts are configured with DNS host name
• loopback address is associated with the name localhost
  • can be substituted for the numeric address

Other

Reserved for special use and not publicly routable:

• 0.0.0.0/8
  • used when a specific address is unknown
  • typically used as a source address by a client seeking a DHCP lease
• 255.255.255.255
  • used to broadcast to the local network when the local network address is not known
• 100.64.0.0/10, 192.0.0.0/24, 192.88.99.0.24, 198.18.0.0/15
  • set aside for variety of special purposes
• 192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24
  • set aside for use in documentation and examples