Category: ipv6

IPv6 – Address Types & Formats ”; Previous Next Hexadecimal Number System Before introducing IPv6 Address format, we shall look into Hexadecimal Number System. Hexadecimal is a positional number system that uses radix (base) of 16. To represent the values in readable format, this system uses 0-9 symbols to represent values from zero to nine and A-F to represent values from ten to fifteen. Every digit in Hexadecimal can represent values from 0 to 15. [Image: Conversion Table]Address Structure An IPv6 address is made of 128 bits divided into eight 16-bits blocks. Each block is then converted into 4-digit Hexadecimal numbers separated by colon symbols. For example, given below is a 128 bit IPv6 address represented in binary format and divided into eight 16-bits blocks: 0010000000000001 0000000000000000 0011001000111000 1101111111100001 0000000001100011 0000000000000000 0000000000000000 1111111011111011 Each block is then converted into Hexadecimal and separated by ‘:’ symbol: 2001:0000:3238:DFE1:0063:0000:0000:FEFB Even after converting into Hexadecimal format, IPv6 address remains long. IPv6 provides some rules to shorten the address. The rules are as follows: Rule.1: Discard leading Zero(es): In Block 5, 0063, the leading two 0s can be omitted, such as (5th block): 2001:0000:3238:DFE1:63:0000:0000:FEFB Rule.2: If two of more blocks contain consecutive zeroes, omit them all and replace with double colon sign ::, such as (6th and 7th block): 2001:0000:3238:DFE1:63::FEFB Consecutive blocks of zeroes can be replaced only once by :: so if there are still blocks of zeroes in the address, they can be shrunk down to a single zero, such as (2nd block): 2001:0:3238:DFE1:63::FEFB Interface ID IPv6 has three different types of Unicast Address scheme. The second half of the address (last 64 bits) is always used for Interface ID. The MAC address of a system is composed of 48-bits and represented in Hexadecimal. MAC addresses are considered to be uniquely assigned worldwide. Interface ID takes advantage of this uniqueness of MAC addresses. A host can auto-configure its Interface ID by using IEEE’s Extended Unique Identifier (EUI-64) format. First, a host divides its own MAC address into two 24-bits halves. Then 16-bit Hex value 0xFFFE is sandwiched into those two halves of MAC address, resulting in EUI-64 Interface ID. [Image: EUI-64 Interface ID]Conversion of EUI-64 ID into IPv6 Interface Identifier To convert EUI-64 ID into IPv6 Interface Identifier, the most significant 7th bit of EUI-64 ID is complemented. For example: [Image: IPV6 Interface ID]Global Unicast Address This address type is equivalent to IPv4’s public address. Global Unicast addresses in IPv6 are globally identifiable and uniquely addressable. [Image: Global Unicast Address]Global Routing Prefix: The most significant 48-bits are designated as Global Routing Prefix which is assigned to specific autonomous system. The three most significant bits of Global Routing Prefix is always set to 001. Link-Local Address Auto-configured IPv6 address is known as Link-Local address. This address always starts with FE80. The first 16 bits of link-local address is always set to 1111 1110 1000 0000 (FE80). The next 48-bits are set to 0, thus: [Image: Link-Local Address]Link-local addresses are used for communication among IPv6 hosts on a link (broadcast segment) only. These addresses are not routable, so a Router never forwards these addresses outside the link. Unique-Local Address This type of IPv6 address is globally unique, but it should be used in local communication. The second half of this address contain Interface ID and the first half is divided among Prefix, Local Bit, Global ID and Subnet ID. [Image: Unique-Local Address]Prefix is always set to 1111 110. L bit, is set to 1 if the address is locally assigned. So far, the meaning of L bit to 0 is not defined. Therefore, Unique Local IPv6 address always starts with ‘FD’. Scope of IPv6 Unicast Addresses: [Image: IPv6 Unicast Address Scope]The scope of Link-local address is limited to the segment. Unique Local Address are locally global, but are not routed over the Internet, limiting their scope to an organization’s boundary. Global Unicast addresses are globally unique and recognizable. They shall make the essence of Internet v2 addressing. Print Page Previous Next Advertisements ”;

IPv6 – Subnetting ”; Previous Next In IPv4, addresses were created in classes. Classful IPv4 addresses clearly define the bits used for network prefixes and the bits used for hosts on that network. To subnet in IPv4, we play with the default classful netmask which allows us to borrow host bits to be used as subnet bits. This results in multiple subnets but less hosts per subnet. That is, when we borrow host bits to create a subnet, it costs us in lesser bit to be used for host addresses. IPv6 addresses use 128 bits to represent an address which includes bits to be used for subnetting. The second half of the address (least significant 64 bits) is always used for hosts only. Therefore, there is no compromise if we subnet the network. [Image: IPv6 Subnetting]16 bits of subnet is equivalent to IPv4’s Class B Network. Using these subnet bits, an organization can have another 65 thousands of subnets which is by far, more than enough. Thus routing prefix is /64 and host portion is 64 bits. We can further subnet the network beyond 16 bits of Subnet ID, by borrowing host bits; but it is recommended that 64 bits should always be used for hosts addresses because auto-configuration requires 64 bits. IPv6 subnetting works on the same concept as Variable Length Subnet Masking in IPv4. /48 prefix can be allocated to an organization providing it the benefit of having up to /64 subnet prefixes, which is 65535 sub-networks, each having 264 hosts. A /64 prefix can be assigned to a point-to-point connection where there are only two hosts (or IPv6 enabled devices) on a link. Print Page Previous Next Advertisements ”;

IPv6 – Addressing Modes ”; Previous Next In computer networking, addressing mode refers to the mechanism of hosting an address on the network. IPv6 offers several types of modes by which a single host can be addressed. More than one host can be addressed at once or the host at the closest distance can be addressed. Unicast In unicast mode of addressing, an IPv6 interface (host) is uniquely identified in a network segment. The IPv6 packet contains both source and destination IP addresses. A host interface is equipped with an IP address which is unique in that network segment.When a network switch or a router receives a unicast IP packet, destined to a single host, it sends out one of its outgoing interface which connects to that particular host. Multicast The IPv6 multicast mode is same as that of IPv4. The packet destined to multiple hosts is sent on a special multicast address. All the hosts interested in that multicast information, need to join that multicast group first. All the interfaces that joined the group receive the multicast packet and process it, while other hosts not interested in multicast packets ignore the multicast information. Anycast IPv6 has introduced a new type of addressing, which is called Anycast addressing. In this addressing mode, multiple interfaces (hosts) are assigned same Anycast IP address. When a host wishes to communicate with a host equipped with an Anycast IP address, it sends a Unicast message. With the help of complex routing mechanism, that Unicast message is delivered to the host closest to the Sender in terms of Routing cost. Let’s take an example of TutorialPoints.com Web Servers, located in all continents. Assume that all the Web Servers are assigned a single IPv6 Anycast IP Address. Now when a user from Europe wants to reach TutorialsPoint.com the DNS points to the server that is physically located in Europe itself. If a user from India tries to reach Tutorialspoint.com, the DNS will then point to the Web Server physically located in Asia. Nearest or Closest terms are used in terms of Routing Cost. In the above picture, when a client computer tries to reach a server, the request is forwarded to the server with the lowest Routing Cost. Print Page Previous Next Advertisements ”;

IPv6 – Special Addresses ”; Previous Next Version 6 has slightly complex structure of IP address than that of IPv4. IPv6 has reserved a few addresses and address notations for special purposes. See the table below: As shown in the table, the address 0:0:0:0:0:0:0:0/128 does not specify anything and is said to be an unspecified address. After simplifying, all the 0s are compacted to ::/128. In IPv4, the address 0.0.0.0 with netmask 0.0.0.0 represents the default route. The same concept is also applied to IPv6, address 0:0:0:0:0:0:0:0 with netmask all 0s represents the default route. After applying IPv6 rule, this address is compressed to ::/0. Loopback addresses in IPv4 are represented by 127.0.0.1 to 127.255.255.255 series. But in IPv6, only 0:0:0:0:0:0:0:1/128 represents the Loopback address. After loopback address, it can be represented as ::1/128. Reserved Multicast Address for Routing Protocols The above table shows the reserved multicast addresses used by interior routing protocol. The addresses are reserved following the same rules of IPv4. Reserved Multicast Address for Routers/Node These addresses help routers and hosts to speak to available routers and hosts on a segment without being configured with an IPv6 address. Hosts use EUI-64 based auto-configuration to self-configure an IPv6 address and then speak to available hosts/routers on the segment by means of these addresses. Print Page Previous Next Advertisements ”;