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Chapter 4: IPv4 and IPv6 Addressing > IPv6 ADDRESSING DETAILS


Let’s take a quick look at some of the differences between IPv4 and IPv6 addressing. The use of the IPv6 address space is determined by the value of the first few bits of an IPv6 address. Routing in IPv6 is similar to IPv4 with CIDR and VLSM, but there are a few points to be made to clarify this.

IPv6 addresses can be provider based, provider independent, or for local use. All provider-based IPv6 addresses for “aggregatable” global unicast packets begin with either 0010 (2) or 0011 (3) in the first four bit positions of the 128-bit IPv6 address.

Typical IPv6 address prefixes would look like:


and so on.

The 64 bits that make up the low-order bits of the IPv6 address must be in a format known as the EUI-64 (64-bit Extended Unique Identifier). Normally, the 48-bit MAC address consists of 3 bytes (24 bits) assigned to the manufacturer and 3 bytes (24 bits) for the serial number of the NIC itself. A typical MAC address would look like 0000:900F:C27E. The next to the last bit in the first byte of this address is the global/local bit, and is usually set to a 0 bit (global). This means that the MAC address is globally assigned and is using the native address assigned by the manufacturer. In EUI-64 format, this bit is flipped and usually ends up being set to a 1 bit (the meaning is flipped too, so in IPv6, 1 here means global). This would make the first byte 02 instead of 00. For example, 0000:900F:C27E becomes 0200:900F:C27E (not always, but this is just a simple example).


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