Identify the appropriate IPv6 addressing scheme to satisfy addressing requirements in a LAN/WAN environment
IPv6 Addresses
The IPv6 128-bit address is divided along 16-bit boundaries. Each 16-bit block is then converted to a 4-digit hexadecimal number, separated by colons. The resulting representation is called colon-hexadecimal. This is in contrast to the 32-bit IPv4 address represented in dotted-decimal format, divided along 8-bit boundaries, and then converted to its decimal equivalent, separated by periods.In short IPv6 addresses are divided into two parts: a 64-bit network prefix, and a 64-bit interface identifier. Further IPv6 classified as follows:
1.Unicast addresses - used to identify each network interface.
2.Anycast addresses - used to identify a group of interfaces at different locations.
3.Multicast addresses - used to deliver one packet to many interfaces
IPv6 does not support the broadcast method. Some IPv6 addresses are used for special purposes, such as the address for loopback which look like as follows:
Identify the appropriate IPv6 addressing scheme to satisfy addressing requirements in a LAN/WAN environment
IPv6 Addresses
IPv6, like the most commonly used IPv4, is an Internet-layer protocol for packet-switched internetworking and provides end-to-end datagram transmission across multiple IP networks. IPv4 simplifies aspects of address assignment (stateless address auto configuration), network renumbering and router announcements when changing network connectivity providers. The IPv6 subnet size has been standardized by fixing the size of the host identifier portion of an address to 64 bits to facilitate an automatic mechanism for forming the host identifier from link-layer media addressing information (MAC address). Network security is also integrated into the design of the IPv6 architecture, including the option of IPsec.
IPv6 Address Notation
IPv6 addresses are different in appearance from IPv4. Of course, they are 128 bits long, so even in binary they would be four times longer than a 32-bit IPv4 address, but in notation that humans read and write the format is still different. Instead of using dotted-decimal in four octets, we use hexadecimal in eight sets of four characters separated by colons, like this:2201:0FA0:080B:2112:0000:0000:0000:0001The use of hex makes IPv6 a little easier to represent all those 128 bits in a shorter format because each character represents 4 bits. But it’s still a long thing to type out, and remember that network people are generally lazy—so we have a couple of truncation methods to make the long addresses even shorter. The first method is that we are allowed to drop leading 0s (0s that appear at the beginning of each set), like so:
2201:FA0:80B:2112:0:0:0:1
That makes for a little less typing and a little more clarity. Pay attention to the fact that dropping 0s at the end of each set is not allowed! Dropping leading 0s does not change the value of the set; dropping 0s at the end does (like removing a 0 from the end of your paycheck amount—not good!)
The second truncation method we can use is to condense contiguous groups of all-0 sets. In our example, there are three sets that are all 0s. We can represent these by a double colon, like this:
2201:FA0:80B:2112::1
IPv6 Address Allocation
An organization called the Internet Corporation for Assigned Network Numbers (ICANN) has the overall responsibility for dividing up the IPv6 address space. They do so with the benefit of a better understanding of the global demand for Internet IP addresses and the luxury of a huge number of addresses to hand out.
The system works like this: First, remember that for the Internet to work well, we need to use route summarization so that the route tables don’t get huge and slow the routers down. Route summarization works best if every router is responsible only for its “branch of the tree,” with smaller branches feeding into larger and larger ones as we get closer to the core or trunk of the tree. This allows the possibility for a single router to advertise a summary that in effect says, “I can reach all North American routes.” That big router connects to other routers that summarize routes for four major Internet service providers (ISPs). Each ISP router connects to smaller ISPs or large enterprise customers, who advertise the summaries that represent the addresses assigned to them. Figure 3.19 gives some idea of how this system works.
Types of IPv6 Addresses
An IPv6 address will be one of the following types. Some will be familiar, but there is one brand-new one, too.
• Unicast: An IPv6 unicast address is the same as an IPv4 unicast address; it is an IP that is assigned to an interface on a host. It can be the source of an IP packet or the destination for one. A packet sent to a unicast address goes to the one host with that address.
• Global unicast: A global unicast IPv6 address is the equivalent of a public, registered IP address. They are Internet routable, globally registered IPs that must be leased from an ISP.
• Unique local: Equivalent to a private IPv4 address; not registered with an ISP and not Internet routable.
• Link local: Every IPv6 interface gives itself a link-local address. The address range is FE80::/10, and usually combines this prefix with the last 64 bits in EUI-64 format. It is roughly equivalent to the Automatic Private IP Address (APIPA) address range of 169.254.0.0/16.
• Multicast: Just like in IPv4, a single IPv6 multicast address is assigned to multiple hosts so that a packet sent to the address may be delivered to multiple hosts more or less at the same time. IPv6 multicast addresses always start with the prefix FF00::/8.
• Anycast: An anycast address is a single address that is assigned to multiple hosts. This is similar to a multicast, except that a packet for the anycast address will be delivered to the one host that is nearest according to the routing protocol’s idea of distance. There is no special prefix for anycast addresses.
There is no such thing as a broadcast in IPv6. Ever. Any requirement for broadcasting is performed by a multicast instead.
IPv6 Address Configuration
For hosts to use IPv6 addresses, an IPv6 protocol stack must be installed. This likely means that you will need to upgrade your router IOS to provide IPv6 support. Then you can choose one of four options for address assignment.
To understand the address assignment choices better, we need to examine the concepts of stateful versus stateless configuration and the EUI-64 address format.
In IPv6, we can use DHCP to assign IP addresses just like in IPv4. The admin must set up the server with a scope of IPv6 addresses to hand out. The mechanisms used to discover and assign addresses are a little different, but the net result is the same. This is called stateful addressing, where the DHCP server keeps track of what hosts have been assigned what IPv6 address—in other words, the state of the host DHCP-wise.
There is another option for dynamic addressing in IPv6 called stateless autoconfiguration. This feature allows a host to choose and configure an address for itself. The host that wants an address learns what the /64 network prefix is on the local link, then appends its MAC address (in a special 64-bit format called EUI-64), thus generating a 128-bit IPv6 address that is unique to that host because it incorporates the unique MAC of the host.
The EUI-64 format is not so difficult to understand. We simply take the 48-bit MAC address and put a special pattern, FFFE, after the first 24 bits (the six OUI characters), followed by the rest of the six hex characters in the host MAC. The only trick is that according to IPv6 rules, the seventh bit in an EUI-64 address must be 1, which identifies that the burned-in MAC address has been modified. This is a little confusing, to be sure, but you can relax because the host determines and configures its EUI-64 address all by itself, if you tell it to. Here’s what an EUI-64 address conversion looks like:
Original MAC:
00-15-C5-CB-42-2B
Original MAC in binary:
00000000-00010101-11000101-11001011-01000010-00101011
7th bit = 0
Change 7th bit to 1:
00000010-00010101-11000101-11001011-01000010-00101011
EUI-64 MAC now :
02-15-C5-CB-42-2B
EUI-64 Address = :0215:C5FF:FECB:422B
So, back to the four choices. The following really simplifies the options :Static configuration: The administrator chooses and assigns a static IPv6 address to the host NIC. It is the admin’s responsibility to choose an address that will function and be valid in the network to which the host is connected.
Static configuration using EUI-64: The administrator manually configures the address with the local /64 network prefix followed by the host’s MAC in EUI-64 format.
Dynamic configuration using DHCP to assign 128-bit address: The host is set to obtain its address from DHCP, and the DHCP server is set up to hand out IPv6 addresses from a scope.
