IPv6 Address Representation

Objectives IPv6 Addressing scheme IPv6 Address Plan IPv6 Address Types IPv6 Address with an Embedded IPv4 Address IPv6 Address Representation for URL IPv6 and Subnetting IPv6 Addressing

IPv6 Addressing Rules 128 bits (or 16 bytes) long: four times as long as its predecessor. 2128 : about 340 billion billion billion billion different addresses Colon hexadecimal notation: addresses are written using 32 hexadecimal digits. digits are arranged into 8 groups of four to improve the readability. Groups are separated by colons 2001:0718:1c01:0016:020d:56ff:fe77:52a3 Note: DNS plays an important role in the IPv6 world (manual typing of IPv6 addresses is not an easy thing, Some zero suppression rules are allowed to lighten this task at least a little. IPv6 Addressing

IPv6 Address Notation: Example 128.91.45.157.220.40.0.0.0.0.252.87.212.200.31.255 IPv6 Addressing

Rule 1- IPv6 Zero Suppression Some types of addresses contain long sequences of zeros. To further simplify the representation of IPv6 addresses, a contiguous sequence of 16-bit blocks set to 0 in the colon hexadecimal format can be compressed to “::”, known as double-colon. For example: link-local address FE80:0:0:0:2AA:FF:FE9A:4CA2  FE80::2AA:FF:FE9A:4CA2. multicast address FF02:0:0:0:0:0:0:2  FF02::2 loopback address 0:0:0:0:0:0:0:1  ::1 IPv6 Addressing

Rule 1- IPv6 Zero Suppression Zero compression can only be used to compress a single contiguous series of 16-bit blocks expressed in colon hexadecimal notation. You cannot use zero compression to include part of a 16-bit block. For example, cannot express FF02:30:0:0:0:0:0:5 as FF02:3::5 correct representation = FF02:30::5 Leading zeroes in every group can be omitted. 2001:718:1c01:16:20d:56ff:fe77:52a3 IPv6 Addressing

Rule 1- IPv6 Zero Suppression To determine the number of 0 bits represented by the “::” count the number of blocks in the compressed address (-) subtract this number from 8 (*) multiply the result by 16. For example FF02::2 two blocks - “FF02” block and “2” block. The number of bits expressed by the “::” is 96 (96 = (8 – 2)16). Zero compression can only be used once in a given address. Otherwise, you could not determine the number of 0 bits represented by each instance of “::”. IPv6 Addressing

IPv6 Prefixes The prefix is the part of the address that indicates the bits that have fixed values or are the bits of the subnet prefix. Prefixes for IPv6 subnets, routes, and address ranges 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 and 21DA:D3:0:2F3B::/64 are IPv6 address prefixes. Note IPv4 implementations commonly use a dotted decimal representation of the network prefix known as the subnet mask. A subnet mask is not used for IPv6. Only the prefix length notation is supported. IPv6 Addressing

IPv6 Prefixes IPv6 Addressing

IPv6 Address Types

IPv6 Addresses: Types and Scopes IPv6 Addressing

IPv6 Address Categories IPv6 Addressing

IPv6 Address Types IPv6 Addressing

Unicast IPv6 Addresses The following types of addresses are unicast IPv6 addresses: Global unicast addresses Link-local addresses Site-local addresses Unique local IPv6 unicast addresses Special addresses IPv6 Addressing

Global Unicast Addresses Equivalent to public IPv4 addresses. Globally routable and reachable on the IPv6 portion of the Internet. Unlike the current IPv4-based Internet, which is a mixture of both flat and hierarchical routing, the IPv6-based Internet has been designed from its foundation to support efficient, hierarchical addressing and routing. The scope, the portion of the IPv6 internetwork over which the address is unique, of a global unicast address is the entire IPv6 Internet. Global scoped communication are identified by high-level 3 bits set to 001 (2000::/3) IPv6 Addressing

Global Unicast Address Each aggregatable global unicast IPv6 address has three parts: Fixed portion set to 001 – The three high-order bits are set to 001. The address prefix for currently assigned global addresses is 2000::/3. Global Routing Prefix – Site Prefix Site prefix assigned to an organization (leaf site) by a provider should be at least a /48 prefix = 45 + high-order bits (001). /48 prefix represents the high-order 48-bit of the network prefix. prefix assigned to the organization is part of the provider’s prefix. Subnet-id - Site With one /48 prefix allocated to an organization by a provider, it is possible for that organization to enable up to 65,535 subnets (assignment of 64-bit’s prefix to subnets). The organization can use bits 49 to 64 (16-bit) of the prefix received for subnetting. Interface-id – Host The host part uses each node’s interface identifier. This part of the IPv6 address, which represents the address’s low-order 64-bit, is called the interface ID. IPv6 Addressing

Global Unicast Address: Example 2001:0410:0110::/48 is assigned by a provider 2001:0410:0110:0002::/64 network subnet within the organization 2001:0410:0110:0002:0200:CBCF:1234:4402 – node address within the subnet Due to this structure, most end sites (regular companies and organizations, as opposed to ISPss) will be assigned IPv6 networks with a 48-bit prefix. These network identifiers have now come to be called 48s or /48s. IPv6 Addressing

Global Unicast Address IPv6 Addressing

Global Unicast Address Allocation IPv6 Addressing

Global Unicast Address Allocation Prefix (hex) Prefix (Binary) Description 2000::/16 0010 0000 0000 0000 Reserved 2001::/16 0010 0000 0000 0001 IPv6 Internet -ARIN,APNIC,RIPE NCC,LACNIC 2002::/16 0010 0000 0000 0 6 to 4 transition mechanisms 2003::/16 0010 0000 0000 0011 IPv6 Internet - RIPE NCCC 2400:0000::/19 2400:2000::/19 2400:4000::/21 0010 0100 0000 0000 - APNIC 2600:0000::/22 2604:0000::/22 2608:0000::/22 260C:0000::/22 0010 0110 0000 0000 0010 0110 0000 0100 0010 0110 0000 1000 0010 0110 0000 1100 -ARIN 2A00:0000::/21 2A01:0000::/23 0010 1010 0000 0000 0010 1010 0000 0001 -RIPE NCC 3FFF::/16 0011 1111 1111 1110 6 Bone IPv6 Addressing

IPv6 Unicast Address Scopes Three types of scopes: Link-local scope Identifies all hosts within a single layer 2 domain. Called as link-local addresses Unique-local scope Identifies all devices reachable within an administrative site or domain typically contains multiple distinct links. Called as unique-local addresses (ULAs) Global scope Identifies all devices reachable across the Internet. Called as global unicast addresses (GUAs) IPv6 Addressing

Local-Use Unicast Addresses There are two types of local-use unicast addresses: Link-local addresses used between on-link neighbors and for Neighbor Discovery Processes. Site-local addresses used between nodes communicating with other nodes in the same site. IPv6 Addressing

Link-local Unicast Address IPv6 link-local addresses are equivalent to IPv4 link-local addresses defined in RFC 3927 that use the 169.254.0.0/16 prefix. IPv4 link-local addresses are known as Automatic Private IP Addressing (APIPA) addresses for computers running current Microsoft Windows operating systems. The scope of a link-local address is the local link. A link-local address is required for Neighbor Discovery (NDP) processes and is always automatically configured, even in the absence of all other unicast addresses. IPv6 Addressing

Link-local Unicast Address Used only between nodes connected on the same local link. When an IPv6 stack is enabled on a node, one link-local address is automatically assigned to each interface of the node at boot time. IPv6 link-local prefix FE80::/10 is used and the interface identifier in Extended Unique Identifier 64 (EUI-64) format is appended as the address’s low-order 64-bit. Bits 11 through 64 are set to 0 (54-bit). Link-local addresses are only for local-link scope and must never be routed between subnets within a site. IPv6 Addressing

Link-local unicast address Because the low-order 64-bit of the link-local address is the interface identifier itself, the length of the link-local prefix is based on a 64-bit length (/64). In IPv6, a node having an aggregatable global unicast address on a local link uses the link-local address of its default IPv6 router rather than the router’s aggregatable global unicast address. If network renumbering must occur, meaning that the unicast aggregatable global prefix is changed to a new one, the default router can always be reached using the link-local address. Link-local addresses of nodes and routers do not change during network renumbering. IPv6 Addressing

Site-Local Address Site-local addresses are equivalent to the IPv4 private address space (10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16). Private intranets that do not have a direct, routed connection to the IPv6 Internet can use site-local addresses without conflicting with global unicast addresses. Site-local addresses are not reachable from other sites, and routers must not forward site-local traffic outside the site. Site-local addresses can be used in addition to global unicast addresses. The scope of a site-local address is the site. A site is an organization network or portion of an organization's network that has a defined geographical location (such as an office, an office complex, or a campus). IPv6 Addressing

Site-Local Address Unlike link-local addresses, site-local addresses are not automatically configured and must be assigned either through stateless or stateful address configuration processes. May be assigned to any nodes and routers within a site. These addresses have the scope of an entire site, or organization. They allow addressing within an organization without need for using a public prefix. Routers will forward datagrams using site-local addresses within the site, but not outside it to the public Internet. Site-local addresses are differentiated from link-local addresses by having a tenth bit of “1” following the nine starting address bits common to all private IPv6 addresses. They begin with “1111 1110 11”. In hexadecimal, they begin with “FE” and then “C” to “F” for the third hex digit So, these addresses start with “FEC”, “FED”, “FEE” or “FEF”. IPv6 Addressing

Site-Local Address - Example For example, a site with ten subnets may assign site-local prefixes such as the following: Subnet 1—FEC0:0:0:0001::/64 Subnet 2—FEC0:0:0:0002::/64 Subnet 3—FEC0:0:0:0003::/64 Subnet 4—FEC0:0:0:0004::/64 Subnet 5—FEC0:0:0:0005::/64 Subnet 6—FEC0:0:0:0006::/64 Subnet 7—FEC0:0:0:0007::/64 Subnet 8—FEC0:0:0:0008::/64 Subnet 9—FEC0:0:0:0009::/64 Subnet 10—FEC0:0:0:000A::/64 IPv6 Addressing

Special IPv6 Addresses The following are special IPv6 addresses: Unspecified address unspecified address (0:0:0:0:0:0:0:0 or ::) is only used to indicate the absence of an address. equivalent to the IPv4 unspecified address of 0.0.0.0. used as a source address for packets attempting to verify the uniqueness of a tentative address. never assigned to an interface or used as a destination address. Loopback address The loopback address (0:0:0:0:0:0:0:1 or ::1) is used to identify a loopback interface, enabling a node to send packets to itself. It is equivalent to the IPv4 loopback address of 127.0.0.1. Packets addressed to the loopback address must never be sent on a link or forwarded by an IPv6 router. IPv6 Addressing

Multicast Addresses

Multicast Address: Overview In IPv6, multicast traffic operates in the same way that it does in IPv4. Arbitrarily located IPv6 nodes can listen for multicast traffic on an arbitrary IPv6 multicast address. IPv6 nodes can listen to multiple multicast addresses at the same time. Nodes can join or leave a multicast group at any time. IPv6 multicast addresses have the first eight bits set to 1111 1111. An IPv6 address is easy to classify as multicast because it always begins with “FF”. Multicast addresses cannot be used as source addresses or as intermediate destinations in a Routing extension header. Beyond the first eight bits, multicast addresses include additional structure to identify their flags, scope, and multicast group. IPv6 Addressing

Multicast Address Main goal of multicasting is having an efficient network to save bandwidth on links by optimizing the number of packets exchanged between nodes In IPv4: 224.0.0.0/3, where the high-order 3-bit of the IPv4 address is set to 111 In IPv6: IPv6 Addressing

Multicast Address IPv6 makes heavy use of multicast addresses in the mechanisms of the protocol such as The replacement of Address Resolution Protocol (ARP) in IPv4 Prefix advertisement Duplicate Address Detection (DAD) Prefix renumbering. Format of the multicast address defines several scopes and types of addresses using the 4-bit fields Flag and Scope. These fields are located after the FF::/8 prefix. The low-order 112-bit of the multicast address is the multicast group ID. IPv6 Addressing

Format of the Multicast Address fields High-order 3-bit of the Flag field is reserved and must be initialized using 0 values. Remaining bit indicates the type of multicast address. IPv6 Addressing

Format of the Multicast Address: Flags field Indicates flags set on the multicast address. The size = 4 bits. The first low-order bit = Transient (T) flag. T = 0  T flag indicates that the multicast address is a permanently assigned (well-known) multicast address allocated by IANA. T = 1  T flag indicates that the multicast address is a transient (non-permanently-assigned) multicast address. The second low-order bit = Prefix (P) flag indicates whether the multicast address is based on a unicast address prefix. RFC 3306 describes the P flag. The third low-order bit = Rendezvous Point Address (R) flag indicates whether the multicast address contains an embedded rendezvous point address. RFC 3956 describes the R flag. IPv6 Addressing

Format of the Multicast Address: Scope Field Indicates the scope of the IPv6 internetwork for which the multicast traffic is intended. The size = 4 bits. In addition to information provided by multicast routing protocols, routers use the multicast scope to determine whether multicast traffic can be forwarded. The most prevalent values for the Scope field are: 1 (interface-local scope) 2 (link-local scope) 5 (site-local scope) For example: Traffic with the multicast address of FF02::2 has a link-local scope. An IPv6 router never forwards this traffic beyond the local link. IPv6 Addressing

Format of the Multicast Address: Scope Field Example of Multicast Addresses with Different Scopes IPv6 Addressing

Format of the Multicast Address: Group ID Field Identifies the multicast group and is unique within the scope. The size = 112 bits. Permanently assigned group IDs are independent of the scope. Transient group IDs are only relevant to a specific scope. Multicast addresses from FF01:: through FF0F:: are reserved, well-known addresses. IPv6 Addressing

Multicast Assigned Address RFC 2373 defines and reserves several IPv6 addresses within the multicast scope for the operation of the IPv6 protocol. These reserved addresses are called multicast assigned addresses. IPv6 Addressing

Solicited-Node Multicast Address For each unicast and anycast address configured on an interface of a node or router, a corresponding solicited-node multicast address is automatically enabled. The solicited-node multicast address is scoped to the local link. Replacement of ARP in IPv4 ARP is not used in IPv6, the solicited-node multicast address is used by nodes and routers to learn the link-layer addresses of neighbor nodes and routers on the same local link. As with ARP in IPv4, knowledge of link-layer addresses of neighbor nodes is mandatory to make link-layer frames to deliver IPv6 packets. Duplicate Address Detection (DAD) DAD is part of NDP. It allows a node to verify whether an IPv6 address is already in use on its local link before using that address to configure its own IPv6 address with stateless autoconfiguration. The solicited-node multicast address is used to probe the local link in search of a specific unicast or anycast address already configured on another node. IPv6 Addressing

Solicited-Node Multicast Address Representations Consists of the prefix FF02::1:FF00:0000/104 + low-order 24-bit of the unicast or anycast address. Low-order 24-bit of the unicast or anycast address is appended to the prefix FF02::1:FF. IPv6 Addressing

Solicited-Node Multicast Address Representations Examples of Solicited-Node Multicast Addresses Made from Unicast Addresses For example, Node A is assigned the link-local address of FE80::2AA:FF:FE28:9C5A and is also listening on the corresponding solicited-node multicast address of FF02::1:FF28:9C5A (the underline highlights the correspondence of the last six hexadecimal digits). Node B on the local link must resolve Node A’s link-local address FE80::2AA:FF:FE28:9C5A to its corresponding link-layer address. Node B sends a Neighbor Solicitation message to the solicited node multicast address of FF02::1:FF28:9C5A. Because Node A is listening on this multicast address, it processes the Neighbor Solicitation message and sends a unicast Neighbor Advertisement message in reply. The result of using the solicited-node multicast address is that address resolutions, a common occurrence on a link, are not required to use a mechanism that disturbs all network nodes. By using the solicited-node address, very few nodes are disturbed during address resolution. In practice, due to the relationship between the Ethernet MAC address, the IPv6 interface ID, and the solicited-node address, the solicited-node address acts as a pseudo-unicast address for very efficient address resolution. IPv6 Addressing

Anycast Address

Anycast Address Anycast addresses can be considered a conceptual cross between unicast and multicast addressing. Unicast  send to this one address Multicast  send to every member of this group Anycast  send to any one member of this group In choosing which member to send to, for efficiency reasons normally send to the closest one - closest in routing terms. So, anycast mean “send to the closest member of this group”. The network itself plays the key role in anycast by routing the packet to the nearest destination by measuring network distance. Anycast addresses use aggregatable global unicast addresses. They can also use site-local or link-local addresses. Note that it is impossible to distinguish an anycast address from a unicast address. The idea behind anycast is to enable functionality that was previously difficult to implement in TCP/IP. Anycast was specifically intended to provide flexibility in situations where we need a service that is provided by a number of different servers or routers but don't really care which one provides it. In routing, anycast allows datagrams to be sent to whichever router in a group of equivalent routers is closest, to allow load sharing amongst routers and dynamic flexibility if certain routers go out of service. Datagrams sent to the anycast address will automatically be delivered to the device that is easiest to reach. In IPv4, organizations that receive a portable IPv4 space from a regional Internet registry such ARIN, RIPE NCC, or APNIC may announce their IPv4 prefix to the global Internet using Border Gateway Protocol (BGP). Routing announcements are done by BGP from several sites on the Internet using the same Autonomous System Number (ASN). Servers using an anycast prefix within these sites can share the same IP address. Packets sent to this anycast prefix by nodes on the global Internet are routed by the BGP routers to the best path in terms of AS-Path. Therefore, the packet is delivered to the nearest destination using the anycast mechanism. IPv6 Addressing

Reserved Anycast Address Also called the subnet-router anycast address. All IPv6 routers are required to support subnet-router anycast addresses for each of their subnet interfaces. Mobile IPv6 is an example of a protocol designed to use anycasting. When a mobile node is away from its home network and wants to discover its home agent IPv6 address, it can use anycasting. The mobile node can send an ICMPv6 “Home Agent Address Discovery Request” message to the Mobile IPv6 home agent anycast address of its home subnet prefix. Then, the mobile node waits until one home agent returns an ICMPv6 “Home Agent Address Discovery Reply” message containing a list of home agents. IPv6 Addressing

So, How many IPv6 addresses can a host have?

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 addresses - even with a single interface. An IPv6 host is assigned the following unicast addresses: A link-local address for each interface Unicast addresses for each interface (which could be a site-local address and one or multiple global unicast addresses) The loopback address (::1) for the loopback interface IPv6 Addressing

IPv6 Addresses for a Host Typical IPv6 hosts are logically multihomed because they have at least two addresses with which they can receive packets a link-local address for local link traffic a routable site-local or global address. Additionally, each host is listening for traffic on the following multicast addresses: The interface-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 on each interface The multicast addresses of joined groups on each interface IPv6 Addressing

And, How many IPv6 addresses can a host have?

IPv6 Addresses for a Router An IPv6 router is assigned the following unicast addresses: A link-local address for each interface Unicast addresses for each interface (which could be a site-local address and one or multiple global unicast addresses) A Subnet-Router anycast address Additional anycast addresses (optional) The loopback address (::1) for the loopback interface IPv6 Addressing

IPv6 Addresses for a Router Additionally, each router is listening for traffic on the following multicast addresses: The interface-local scope all-nodes multicast address (FF01::1) The interface-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 on each interface The multicast addresses of joined groups on each interface IPv6 Addressing

IPv6 Interface Identifiers The last 64 bits of an IPv6 address are the interface identifier that is unique to the 64-bit prefix of the IPv6 address. The following are the ways in which an IPv6 interface identifier is determined: A 64-bit interface identifier that is derived from the Extended Unique Identifier (EUI)-64 address. The 64-bit EUI-64 address is defined by the Institute of Electrical and Electronic Engineers (IEEE). EUI-64 addresses are either assigned to a network adapter or derived from IEEE 802 addresses. This is the default behavior for IPv6 in Windows XP and Windows Server 2003. As defined in RFC 3041, it might have a temporarily assigned, randomly generated interface identifier to provide a level of anonymity when acting as a client. IPv6 Addressing

IPv6 Interface Identifiers As defined in RFC 2472, an interface identifier can be based on link-layer addresses or serial numbers, or randomly generated when configuring a Point-to-Point Protocol (PPP) interface and an EUI-64 address is not available. It is assigned during manual address configuration. It is a permanent interface identifier that is randomly generated to mitigate address scans of unicast IPv6 addresses on a subnet. This is the default behavior for IPv6 in Windows Vista and Windows Server “Longhorn.” You can disable this behavior with the netsh interface ipv6 set global randomizeidentifiers=disabled command. IPv6 Addressing

EUI-64 address-based interface identifiers

IPv6 Modified EUI-64 Format Stateless autoconfiguration is a mechanism that allows nodes on a network to configure their IPv6 addresses themselves without any intermediary device, such as a DHCP server. The link-local address and stateless autoconfiguration are functions of IPv6 that automatically expand the Ethernet MAC address based on a 48-bit format into a 64-bit format (EUI-64). The conversion from 48-bit to 64-bit is a two-step operation. IPv6 Addressing

The IPv6 Modified EUI-64 Format It is essential that all devices on the same network use the same mapping technique The most common type of layer 2 addresses are IEEE 802 MAC addresses. Layer 2 addresses= 48 bits, arranged into two blocks of 24. Upper 24 bits = organizationally unique identifier (OUI), with different values assigned to individual organizations Lower 24 bits = device identifier EUI-64 Format It is similar to the 48-bit MAC format, except that while the OUI remains at 24 bits, the device identifier becomes 40 bits instead of 24. This provides gives each manufacturer 65,536 times as many device addresses within its OUI. n IPv4, IP addresses have no relationship to the addresses used for underlying data link layer network technologies. A host that connects to a TCP/IP network using an Ethernet network interface card (NIC) has an Ethernet MAC address and an IP address, but the two numbers are distinct and unrelated in any way. IP addresses are assigned manually by administrators without any regard for the underlying physical address. With the overhaul of addressing in IPv6, an opportunity presented itself to create a better way of mapping IP unicast addresses and physical network addresses. Implementing this superior mapping technique was one of the reasons why IPv6 addresses were made so large. With 128 total bits, as we saw in the previous topic, even with a full 45 bits reserved for network prefix and 16 bits for site subnet, we are still left with 64 bits to use for the interface identifier, which is analogous to the host ID under IPv4. Having so many bits at our disposal gives us great flexibility. Instead of using arbitrary “made-up” identifiers for hosts, we can base the interface ID on the underlying data link layer hardware address, as long as that address is no greater than 64 bits in length. Since virtually all devices use layer two addresses of 64 bits or fewer, there is no problem in using those addresses for the interface identifier in IP addresses. This provides an immediate benefit: it makes networks easier to administer, since we don't have to record two arbitrary numbers for each host. The IP address can be derived from the MAC address and the network identifier. It also means we can in the future tell the IP address from the MAC address and vice-versa. IPv6 Addressing

Converting 48-Bit MAC Addresses to IPv6 Modified EUI-64 Identifiers Take the 24-bit OUI portion, the left-most 24 bits of the Ethernet address, and put them into the left-most 24 bits of the interface ID. Take the 24-bit local portion (the right-most 24 bits of the Ethernet address) and put it into the right-most 24 bits of the interface ID. In the remaining 16 bits in the middle of the interface ID we put the value “11111111 11111110” (“FFFE” in hexadecimal). The address is now in EUI-64 form. Change the “universal/local” bit (bit 7 from the left) from a zero to a one. This gives us the modified EUI-64 interface ID. We change the seventh bit from zero to one, which changes the first octet from “39” to “3B”. The identifier thus becomes “3B-A7-94-FF-FE-07-CB-D0”, or in IPv6 colon hexadecimal notation, 3BA7:94FF:FE07:CBD0. The first 64 bits of the device's address are supplied using the global unicast address format. The only drawback of this technique is that if the physical hardware changes, so does the IPv6 address. IPv6 Addressing

IPv6 Address with an Embedded IPv4 Address IPv4-compatible IPv6 address is a special unicast IPv6 address used by transition mechanisms on hosts and routers to automatically create IPv4 tunnels to deliver IPv6 packets over IPv4 networks. Address is made up of six high-order fields of 16-bit hexadecimal values, represented by X characters, followed by four low-order fields of 8-bit decimal values (IPv4 address), represented by d characters (for a total of 32 bits). IPv6 Addressing

IPv6 Address with an Embedded IPv4 Address Two kinds of IPv6 addresses have an embedded IPv4 address: IPv4-compatible IPv6 address Used to establish an automatic tunnel to carry IPv6 packets over IPv4 networks. related to a transition mechanism of the IPv6 protocol. IPv4-mapped IPv6 address Used only on the local scope of nodes having both IPv4 and IPv6 stacks. Nodes use IPv4-mapped IPv6 addresses internally only. These addresses are never known outside the node itself and should not go on the wire as IPv6 addresses. IPv6 Addressing

IPv6 Address with an Embedded IPv4 Address IPv4-compatible IPv6 address IPv4-mapped IPv6 address IPv6 Addressing

IPv6 Address Representation for URL colon (:) character is already defined to specify an optional port number for example: www.example.net:8080/index.html https://www.example.com:8443/abc.html In IPv6, the URL parser of Internet browsers must be able to differentiate between the colon of a port number and the colon in an IPv6 address. To identify the IPv6 address while still keeping the colon character for URL format (port number): the IPv6 address must be enclosed in brackets after the brackets, the port number may be added, followed by the directory and filename. [3ffe:b80:c18:1::50]:8080/index.html https://[2001:410:0:1:250:fcee:e450:33ab]:8443/abc.html IPv6 addresses inside brackets should normally be used for diagnostic purposes only or when the naming service (DNS) is unavailable. Because IPv6 addresses are longer than IPv4 addresses, users tend to use the DNS and the fully qualified domain name (FQDN) format instead of the IPv6 address in hexadecimal representation. IPv6 Addressing

IPv6 and Subnetting The only acceptable form to represent a network mask in IPv6 is CIDR notation. Although IPv6 addresses are in hexadecimal format, the network mask value is still a decimal value. IPv6 Addressing