Understanding the IPv6 Addressing Structure
If you have been using IPv4, and understand IPv4 addressing, then it should be easy for you to understand the IPv6 addressing structure. The most difficult thing to understand about the addressing is that the underlying drivers in IPv6 addressing are different than in IPv4 addressing. Those drivers will be discussed later.
First, let’s take a look at a comparison between IPv4 and IPv6 addresses. IPv4 has 32 bit addresses that translates to 232 (4,294,967,296) or 4.3 Billion addresses. IPv6, conversely, has 128 bit addresses that translates to 2128 (340,282,366,920,938,000,000,000,000,000,000,000,000) or 0.34 Duodecillion (0.34×1039) addresses. Obviously, IPv6 has a significantly greater address space than IPv4. Now, let’s look at the actual address structure. IPv4 addresses are traditionally represented by 4 blocks of 8 bytes such as 192.168.20.240. Note that each of the 4 blocks uses a decimal number between 0 and 255. IPv6 addresses are broken into eight 16-bit hexadecimal fields separated by colons. Each field will be between 0000 and FFFF.
IPv6 address examples include:
2001:0BA1:0000:0000:0000:0000:0000:0001 2001:BA1:0:0:0:0:0:1 2001:BA1:0:0:AAAA:0:0:1
A new notation with IPv6 is the use of the double colon “::” which is used to replace the zeros between the colons. The double colon can only be used once in an address and examples include:
2001:BA1::1 2001:BA1::FFFF:0:0:1 ::1 (IPv6 loopback address)
IPv6 addresses also utilize CIDR notation, similar to IPv4, but with a larger address range. A /32 is a typical allocation from a Regional Internet Registry to a carrier. This provides the carrier with 216 /48s (a typical site allocation) and 232 /64s (a typical LAN segment allocation).
In essence, IPv6 addresses are broken into two parts, the network identifier and the host identifier. The network identifier is normally represented by the first 64 bits of the address and tells the world where you are. The host identifier is represented by the second 64 bits of the address and identifies who you are. This is an important concept for two reasons. First, the network identifier provides the ability to leverage hierarchical routing infrastructures. This is critical due to the enormous size of the IPv6 address space and if care is not taken, routing tables can explode and become unmanageable. Secondly, the 64-bit host identifier provides the ability to support new features in IPv6 like stateless auto configuration where nodes can automatically join networks without any pre-configuration.
There are three types of IPv6 addresses: Unicast addresses are used to identify a single interface; Multicast addresses identify a group of interfaces and a packet is delivered to all of the interfaces in the group; and Anycast addresses identify a set of interfaces where a packet is delivered to the closest member of the set. An interesting point to note is that IPv6 does not use broadcast addresses, multicast is used to replace the IPv4 broadcast functionality.
IPv6 addresses are assigned to interfaces, and an interface may have multiple IPv6 addresses. Each interface must have a Link-Local unicast address. Since multiple addresses may be assigned to a single interface, then that interface can be part of multiple logical IPv6 networks at the same time. This could provide network architects tremendous flexibility in designing IPv6 networks.
An important point to remember is that IPv6 is not IPv4. Many engineers have tried to apply IPv4 concepts to IPv6 addressing, and it does not usually end well. Leverage industry best practices and make sure to use a /64 for each LAN segment and stick with /48s or /56s for each site.
Don’t forget to read our other Tech Tips on Understanding the IPv6 protocol header and IPv6 transition mechanisms.
If you interested in discovering more about IPv6, you can by checking out Safari’s IPv6 Networking: A Safari Guide.
Safari Books Online has the content you need
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About this author
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Dale Geesey (CISSP/PMP) is a security, networking and IT professional with over 20 years of experience working in the federal and carrier community. His primary focus is on IPv6, Cyber Security, Health IT and next generation technologies. He has been supporting Government and commercial IPv6 Transition activities since 2004. Specializing in the introduction of advanced and next generation technologies, he has supported numerous technology efforts for government organizations including VA, DoD, Army, SBA, DISA, NSA, SBA, Navy, NIST, OMB, FBI, and NATO. Dale is currently the Chief Operating Officer at Auspex Technologies. |
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