[size=3
0pt]
WWW.OPENGUYS.ORG [/size]
What is IP version 6 !. IPv6 AddressingTHE IPV6 ADDRESS SPACE.The most obvious distinguishing feature of IPv6 is its use of much larger ad-dresses. The size of an address in IPv6 is 128 bits, a bit-string that is four times longer than the 32-bit IPv4 address. A 32-bit address space allows for 232, or 4,294,967,296, possible addresses. A 128-bit address space allows for 2128, or 340,282,366,920,938,463,463,374,607,431,768,211,456 (or 3.4 × 1038), possible addresses.
In the late 1970s, when the IPv4 address space was designed, it was unimaginable that it could ever be exhausted. However, due to changes in technology and an allocation practice that did not anticipate the recent explosion of hosts on the Internet, the IPv4 address space was consumed to the point that by 1992, it was clear a replacement would be necessary.
With IPv6, it is even harder to conceive that the IPv6 address space will ever be consumed. To help put this number in perspective, a 128-bit address space provides 665,570,793,348,866,943,898,599 (6.65 × 1023) addresses for every square meter of the Earth’s surface.
It is important to remember that the decision to make the IPv6 address 128 bits in length was not so that every square meter of the Earth could have 6.65 × 1023 addresses. Rather, the relatively large size of the IPv6 address is designed to be divided into hierarchical routing domains that reflect the topology of the modern-day Internet. The use of 128 bits allows for multiple levels of hierarchy and flexibility in designing hierarchical addressing and routing that is currently lacking on the IPv4-based Internet.
ADDRESSES PER SQUARE METER OF THE EARTH
The number of 6.65 × 1023 addresses for every square meter of the Earth’s surface is derived from the fact that the surface of the Earth is approximately
197,399,019 square miles and there are 2.59 × 106 square meters per square mile. So, the Earth’s surface is 197,399,019 × 2.59 × 106, or 511,263,971,197,990 square meters. Therefore, there are 340,282,366,920,938,463,463,374,607,431,768, 211,456 / 511,263,971,197,990, or 665,570,793,348,866,943,898,599 (or 6.65 × 1023) addresses for each square meter of the Earth’s surface.
It is easy to get lost in the vastness of the IPv6 address space. As we will discover, the unthinkably large 128-bit IPv6 address that is assigned to an interface
on a typical IPv6 host is composed of a 64-bit subnet identifier and a 64-bit interface identifier (a 50-50 split between subnet space and interface space). The 64 bits of subnet identifier leave enough addressing room to satisfy
the addressing requirements of three levels of Internet service providers (ISPs) between your organization and the backbone of the Internet and the addressing needs of your organization. The 64 bits of interface identifier accommodate
the mapping of current and future link-layer media access control (MAC) addresses.
Current Allocation
Similar to the way in which the IPv4 address space was divided into unicast ad-dresses (using Internet address classes) and multicast addresses, the IPv6 address space is divided on the basis of the value of high-order bits. The high-order bits and their fixed values are known as a Format Prefix (FP).
CURRENT ALLOCATION OF THE IPV6 ADDRESS SPACE…………
Allocation Format Prefix (FP) Fraction of Address Space.
Reserved
0000 0000
1/256
Unassigned
0000 0001
1/256
Reserved for Network Service Access Point
(NSAP) allocation
0000 001
1/128
Unassigned
0000 010
1/128
Unassigned
0000 011
1/128
Unassigned
0000 1
1/32
Unassigned
0001
1/16
Aggregatable global unicast addresses
001
001
Unassigned
010
1/8
Unassigned
Unassigned
011
100
1/8
1/8
Unassigned
101
1/8
Unassigned
110
1/8
Unassigned
1110
1/16
Unassigned
1111 0
1/32
Unassigned
1111 10
1/64
Unassigned
1111 110
1/128
Link-local unicast addresses
1111 1110 10
1/1024
Site-local unicast addresses
1111 1110 11
1/1024
Multicast addresses
1111 1111
1/256
IPV6 ADDRESS SYNTAX
IPv4 addresses are represented in dotted-decimal format. The 32-bit IPv4 ad-dress is divided along 8-bit boundaries. Each set of 8 bits is converted to its decimal equivalent and separated by periods. For IPv6, the 128-bit address is divided along 16-bit boundaries, and each 16-bit block is converted to a 4-digit hexadecimal number and separated by colons. The resulting representation is called colon hexadecimal.
The following is an IPv6 address in binary form
0010000111011010000000001101001100000000000000000010111100111011
0000001010101010000000001111111111111110001010001001110001011010
The 128-bit address is divided along 16-bit boundaries:
001000011101101 00000011010011 0000000000000000 0010111100111011
0000001010101010 0000000011111111 1111111000101000 1001110001011010
Each 16-bit block is converted to hexadecimal and delimited with colons. The result is:
21DA:00D3:0000:2F3B:02AA:00FF:FE28:9C5A
IPv6 address representation is further simplified by suppressing the leading zeros within each 16-bit block. However, each block must have at least a single digit. With leading zero suppression, the result is 21DA:D3:0:2F3B:2AA:FF:FE28:9C5A.
NUMBER SYSTEM CHOICE FOR IPV6
Hexadecimal (the Base16 numbering system), rather than decimal (the Base10 numbering system), is used for IPv6 because it is easier to convert between hexadecimal and binary than it is to convert between decimal and binary. Each hexadecimal digit represents four binary digits. With IPv4, decimal is used to make the IPv4 addresses more palatable for humans and a 32-bit address becomes 4 decimal numbers separated
by the period (.) character. With IPv6, dotted decimal representation would result in 16 decimal numbers separated by the period (.) character.
IPv6 addresses are so large that there is no attempt to make them palatable to most humans, with the exception of some types of IPv6 ad-dresses that contain embedded IPv4 addresses. Configuration of typical end systems is automated and end users will almost always use names rather than IPv6 addresses. Therefore, the addresses are expressed in a way to make them more palatable to computers and IPv6 network administrators who understand the semantics and relationship of hexadecimal and binary numbers.
CONVERTING BETWEEN BINARY, HEXADECIMAL, AND DECIMAL NUMBERS
Binary Hexadecimal
Decimal
0000 0 0
0001 1 1
0010 2 2
0011 3 3
0100 4 4
0101 5 5
0110 6 6
0111 7 7
1000 8 8
1001 9 9
1010 A 10
1011 B 11
1100 C 12
1101 D 13
1110 E 14
1111 F 15
Compressing Zeros
Some types of IPv6 addresses contain long sequences of zeros. To further simplify
the representation of IPv6 addresses, a single contiguous sequence of 16-bit blocks set to 0 in the colon hexadecimal format can be compressed to ::, known as a double colon.
For example, the link-local address of FE80:0:0:0:2AA:FF:FE9A:4CA2 can be compressed to FE80::2AA:FF:FE9A:4CA2. The multicast address FF02:0:0:0:0:0:0:2 can be compressed to FF02::2.
IPv6 Prefixes
The prefix is the part of the address where the bits have fixed values or are the bits of a route or subnet identifier. Prefixes for IPv6 subnet identifiers and routes are expressed in the same way as Classless Inter-Domain Routing (CIDR) notation
for IPv4. An IPv6 prefix is written in address/prefix-length notation. For example, 21DA:D3::/48 is a route prefix and 21DA:D3:0:2F3B::/64 is a subnet prefix. As described earlier in this chapter, the 64-bit prefix is used for individual subnets to which nodes are attached. All subnets have a 64-bit pre-fix. Any prefix that is less than 64 bits is a route or address range that is summarizing a portion of the IPv6 address space.
One Thing to keep in mind …
IPv4 implementations commonly use a dotted decimal representation of the network prefix known as the subnet mask. A sub-net mask is not used for IPv6. Only the prefix length notation is supported.
An IPv6 prefix is relevant only for routes or address ranges, not for individualunicast addresses. In IPv4, it is common to express an IPv4 address with its prefix length. For example, 192.168.29.7/24 (equivalent to 192.168.29.7 with the subnet mask 255.255.255.0) denotes the IPv4 address 192.168.29.7 with a 24-bit subnet mask. Because IPv4 addresses are no longer class-based, you can-not assume the class-based subnet mask based on the value of the leading octet. The prefix length is included so that you can determine which bits identify the subnet and which bits identify the host on the subnet. Because the number of bits used to identify the subnet in IPv4 is variable, the prefix length is needed to separate the subnet ID from the host ID.
In IPv6, however, there is no notion of a variable length subnet identifier. At the individual IPv6 subnet level for currently defined unicast IPv6 addresses, the number of bits used to identify the subnet is always 64 and the number of bits used to identify the host on the subnet is always 64. Therefore, while unicast IPv6 addresses written with their prefix lengths are permitted in RFC 2373, in practice their prefix lengths are always 64 and therefore do not need to be expressed. For example, there is no need to express the IPv6 unicast address FEC0::2AC4: 2AA:FF:FE9A:82D4 as FEC0::2AC4:2AA:FF:FE9A:82D4/64. Due to the 50-50 split of subnet and interface identifiers, the unicast IPv6 address FEC0::2AC4:2AA: FF:FE9A:82D4 implies that the subnet identifier is FEC0:0:0:2AC4::/64.
TYPES OF IPV6 ADDRESSES
There are three types of IPv6 addresses:
Unicast
A unicast address identifies a single interface within the scope of the type of address. The scope of an address is the region of the IPv6 network over which the address is unique. With the appropriate unicast routing topology, packets addressed to a unicast address are delivered to a single interface. To accommodate load-balancing systems, RFC 2373 allows for multiple interfaces to use the same address as long as they appear as a single interface to the IPv6 implementation
on the host.
Multicast
A multicast address identifies zero or more interfaces. With the appropriate multicast routing topology, packets addressed to a multicast address are delivered to all interfaces identified by the address.
Anycast
An anycast address identifies multiple interfaces. With the appropriate unicast routing topology, packets addressed to an anycast address are delivered to a single interface—the nearest interface that is identified by the address. The nearest interface is defined as being the closest in terms of routing distance. A multicast address is used for one-to-many communication, with delivery to multiple interfaces. An anycast address is used for one-to-one-of-many communication, with delivery to a single interface.
In all cases, IPv6 addresses identify interfaces, not nodes. A node is identified by any unicast address assigned to any one of its interfaces.
IPV6 ADDRESSES FOR A HOST
An IPv4 host with a single network adapter typically has a single IPv4 address assigned to that adapter. An IPv6 host, however, usually has multiple IPv6 ad-dresses assigned to each adapter. The interfaces on a typical IPv6 host are as-signed the following unicast addresses:
• A link-local address for each interface
• Additional unicast addresses for each interface (which could be a site local address and one or multiple global addresses)
• The loopback address (::1) for the loopback interface
Typical IPv6 hosts are always logically multi homed because they always have at least two addresses with which they can receive packets—a link-local address for local link traffic and a routable site-local or global address. Additionally, each interface on an IPv6 host is listening for traffic on the following multicast addresses:
• The node-local scope all-nodes multicast address (FF01::1)
• The link-local scope all-nodes multicast address (FF02::1)
• The solicited-node address for each unicast address
• The multicast addresses of joined groups
IPV6 ADDRESSES FOR A ROUTER
The interfaces on an IPv6 router are assigned the following unicast addresses:
• A link-local address for each interface
• Additional unicast addresses for each interface (which could be a site-local address and one or multiple global addresses)
• The loopback address (::1) for the loopback interface
Additionally, the interfaces of an IPv6 router are assigned the following anycast addresses:
• A Subnet-Router anycast address for each subnet
• Additional anycast addresses (optional)
Additionally, the interfaces of an IPv6 router are listening for traffic on the following multicast addresses:
• The node-local scope all-nodes multicast address (FF01::1)
• The node-local scope all-routers multicast address (FF01::2)
• The link-local scope all-nodes multicast address (FF02::1)
• The link-local scope all-routers multicast address (FF02::2)
• The site-local scope all-routers multicast address (FF05::2)
• The solicited-node address for each unicast address
• The multicast addresses of joined groups
SUBNETTING THE IPV6 ADDRESS SPACE
Just as in IPv4, the IPv6 address space can be divided by using high-order bits that do not already have fixed values to create subnetted network prefixes. These are used either to summarize a level in the routing or addressing hierarchy (with a prefix length less than 64), or to define a specific subnet or network segment (with a prefix length of 64). IPv4 subnetting differs from IPv6 subnetting in the definition of the host ID portion of the address. In IPv4, the host ID can be of varying length, depending on the subnetting scheme. For currently defined unicast IPv6 addresses, the host ID is the interface ID portion of the IPv6 unicast address and is always a fixed size of 64 bits.
Subnetting for NLA IDs
If you are an ISP, subnetting the IPv6 address space consists of using subnetting
techniques to divide the NLA ID portion of a global address in a manner that allows for route summarization and delegation of the remaining address space for different portions of your network, for downstream providers, or for individual customers. The global address has a 24-bit NLA ID field to be used by the various layers of ISPs between a top-level aggregator (a global ISP identified
by the TLA ID) and a customer site.
For a global address allocated to a top-level aggregator, the first 16 bits of the address are fixed and correspond to the FP (set to 001) and the TLA ID (13 bits in length). The TLA ID is followed by the Res portion, which consists of 8 reserved bits set to 0. Therefore, for subnetting of the NLA ID portion of a global address, the first 24 bits are fixed. In a global address, the Res bits are never shown due to the suppression of leading zeros in IPv6 colon hexadecimal
notation.
Subnetting the NLA ID portion of a global address requires a two-step procedure:
1. Determine the number of bits to be used for the subnetting.
2. Enumerate the new subnetted network prefixes.
The subnetting technique described here assumes that subnetting is done by dividing the 24-bit address space of the NLA ID using the high-order bits in the NLA ID that do not already have fixed values. While this method promotes hierarchical addressing and routing, it is not required. For example, you can also create a flat addressing space for the NLA ID by numbering the subnets from 0 to 16,777,215.
Step 1: Determining the Number of Subnetting Bits
The number of bits being used for subnetting determines the possible number of new subnetted network prefixes that can be allocated to portions of your net-work based on geographical, customer segment, or other divisions. In a hierarchical
routing infrastructure, you need to determine how many network prefixes, and therefore how many bits, you need at each level in the hierarchy. The more bits you choose for the various levels of the hierarchy, the fewer bits you will have available to enumerate individual subnets in the last level of the hierarchy. The last level in the hierarchy is used to assign 48-bit prefixes to customer sites.
For example, a network designer at a large ISP decides to implement a two-level hierarchy reflecting a geographical/customer segment structure and uses 8 bits for the geographical level and 8 bits for the customer segment level.
This means that each customer segment in each geographical location has only 8 bits of subnetting space left (24 ? 8 ?
, or only 256 (= 28) 48-bit prefixes per customer segment. On any given level in the hierarchy, you will have a number of bits that are already fixed by the next level up in the hierarchy (f ), a number of bits used for subnetting at the current level in the hierarchy (s), and a number of bits remaining
for the next level down in the hierarchy (r). At all times, f + s + r = 24.
IPV4 ADDRESSES AND IPV6 EQUIVALENTS
To summarize the relationships between IPv4 addressing and IPv6 addressing, Table 3-8 lists both IPv4 addresses and addressing concepts and their IPv6 equivalents.
IPV4 ADDRESSING CONCEPTS AND THEIR IPV6 EQUIVALENTS
IPv4 Address IPv6 Address
Internet address classes Not applicable in IPv6
Multicast addresses (224.0.0.0/4) IPv6 multicast addresses (FF00::/8)
Broadcast addresses Not applicable in IPv6
Unspecified address is 0.0.0.0 Unspecified address is ::
Loopback address is 127.0.0.1 Loopback address is ::1
Public IP addresses Aggregatable global unicast addresses
Private IP addresses (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16) Site-local addresses (FEC0::/48)
