ENVS 1200 Lecture Notes - Lecture 35: Icann
13 May 2018
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ENVS 1200 Lecture 35 Notes – IP Addresses
Introduction
• You know that DNS translates domain names into IP addresses.
• You also know that IP addresses and domain names are registered and allocated by
ICANN.
• This section provides more information about the IP addressing system used with IPv4.
• IPv6 is outside the scope of our discussion.
• An IPv4 address is 32 bits long.
• Every node on the Internet has a unique address.
• As you are aware, the 32 bits are divided into four octets for easier reading
• In the earlier days of the Internet, these octets also identified the assignee to some
extent
• However that is less true today.
• Nonetheless, IP addresses are still assigned in blocks.
• The addresses in a block are contiguous, and the number of addresses in a block must
be a power of two.
• A block is assigned by specifying a given number of bits, from left to right
• The remaining bits represent addresses in the block.
• For example, if your organization is issued a block starting with the 28 bits to the left of
the dividing line, the four remaining bits would provide a block of sixteen addresses for
computers within your organization.
• Your organization could allocate these sixteen addresses any way it wishes.
• The first address in the block is defined as the network address for your organization
• It is used for routing.
• Traditionally, most blocks are larger than sixteen addresses, and IP addresses are usually
divided into three levels, and in some cases four or more.
• An IP address divided into three levels; the top level is, of course, the network address.
• The remaining bits are divided into sub networks, or subnets.
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