ENVS 1000 Lecture Notes - Lecture 37: Ipv6 Address, Directory Service
10 May 2018
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ENVS 1000 Lecture 37 Notes – Bit Group
Introduction
• IP addresses are also called logical addresses.
• There are two standards for IP addresses.
• The older system, IPv4, specifies 32-bit addresses.
• To make these easier for humans to read, they are generally separated into 8-bit groups
called octets, delimited by dots.
• Each octet is written as a decimal number from 0 to 255.
• A tpial address ight e writte as 8.8.5. it’s Wikipedia, for eample.
• IPv6, which is intended to supplant IPv4, specifies 128-bit addresses.
• These are expressed as eight groups of four-digit hexadecimal numbers separated by
colons.
• To simplify the written description somewhat, leading zeros and zero values in one or
more consecutive groups can be eliminated.
• A typical IPv6 address might look like this: 6E:2A20: 35C:66C0:0:5500.
• This one is tricky: there are two consecutive groups of 0 between the empty colons in
this example.
• The: 0: is required to avoid ambiguity. Otherwise, you would not be able to tell which
pair of empty colons had the two groups of 0.
• Needless to say, user-friendly names take on even more importance when working with
IPv6!
• Before a message is sent by an application to the transport layer for data transmission,
the address is translated, if necessary, from user-friendly to IP address using an
application-support program that utilizes a global domain name directory service.
• We will expand our discussion of DNS, the domain name system service
• In addition to the message and the IP address to whom the message is being sent, the
transport identifies the application that created the message and the application that is
to receive the message with port addresses, or more commonly, port numbers.
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