Each device that participates in networking activities must have a unique IP address. Network services that use TCP/IP identify other network hosts by using IP addresses. The IP address provides the exact location of a host device on a network. If the internet protocol determines that a destination address is on the local network, it transmits the packet directly to the network host. If it is determined that the destination IP address is not on the local network, the internet protocol looks for a route to a remote host. An address on the local network is a local address and on not on the local network is a remote address. If a route is found, the packet is sent using that route. If no route is found, then the packet is sent to the default gateway for the source host. A gateway connects networks using different communication protocols.
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An IP address includes a network identifier and a host identifier. The network identifier is used to identify the network where the host is located. All systems that are on the same physical network must have the same network identifier. The host identifier identifies a workstation, server, router, or other host within a network. The address assigned to each host must be unique to the network identifier.
The 128-bit IPv6 address is divided into 16-bit boundaries. The 16-bit blocks are then converted to a 4-digit hexadecimal number, separated by colons. This representation is called colon-hexadecimal. This is in contrast to 32-bit IPv4 address represented in the dotted-decimal format, divided into 8-bit boundaries, and then converted to its decimal equivalent, and separated by periods.
IPv6 addresses do not need to be configured manually. Unlike in IPv4, DHCP is not used in IPv6 to configure IP addresses and subnet masks automatically. The link-local scope of an IPv6 address is always configured automatically. Addresses with other scopes, for example global, are configured by router advertisements.
Static and Dynamic Addresses
A static IP address is an address that does not change over time unless altered manually. It is used when an IP address or network location has to remain the same consistently. A good example of this would be a web server. If you go to www.google.co.uk you are really going to the IP address of 66.102.9.147. If this were to change it would not be possible to access Google.co.uk unless you knew the new IP address or until Google updated their DNS records.
A Dynamic IP address is an address that changes every time the device connects to a network and is assigned an IP address. It is mostly commonly used when a consistent IP address is not necessary. Dynamic IP’s are used in large networks where computers are frequently reconfigured, or where a limited number of IP address are available to share between many computers.
IPv6 Unicast Addresses
IPv6 Unicast
IPv6 Unicast addresses are generically structured as a two part address: a 64-bit Topology part, used by routers to forward a packet to its intended destination network, and a 64-bit Interface Identifier, that identifies a particular end point.
There are several types of unicast addresses in IPv6 unicast: global unicast, link-local unicast, and unique-local unicast. There are also some special-purpose subtypes of global unicast, for example IPv6 addresses with embedded IPv4 addresses or Loopback address. Additional address types or subtypes may be defined in the future.
Elements of a Unicast Address
Prefix – e.g. FC00::/7 is a prefix to identify Local IPv6 unicast addresses.
Global IDs are 40-bit global identifiers used to create a globally unique prefix
Subnet IDs are 16-bit identifiers used to identify a subnet within the site
Interface ID is a 64-bit Interface identifier that indicates the interface of a node
Global Unicast
Global Unicast Addresses of this type are designed to be aggregated or summarized to produce an efficient routing infrastructure. They are the IPv6 equivalent of public IPv4 addresses. Unlike the current IPv4-based Internet, which has the mixture of both flat and hierarchical routing, IPv6 has been designed from the ground up to support hierarchical addressing and routing. Global unicast addresses are globally routable and reachable on the IPv6 section of the Internet. The region of the Internet over which the global unicast address is unique is the entire IPv6 Internet.
IPv6 global unicast addresses are assigned from the prefix 2000::/3. Global unicast address assignments are made to Regional Internet Registries, and the address blocks that have been assigned are registered in the IANA IPv6 Global Unicast Address Assignment Registry. All other address prefixes are currently unallocated, and should not be seen in the source or destination address of an IPv6 packet in the context of global routing.
Link-Local Addresses
Link-local addresses are network addresses that are intended only for communications within one segment of a local network or a point-to-point connection. Link-locals allow addressing hosts without using a globally-routable address prefix. Routers will not forward a packet with link-local addresses.
Link-local addresses are often used for network address configuration when there is no external source of network addressing information is available. This addressing is accomplished by the host operating system using a process called stateless address auto configuration. This is possible in both IPv4 and in IPv6.
IPv6 hosts automatically assign their interfaces a unique address based on the IEEE 802 MAC address.
Unique Local Addresses
Unique Local Addresses are similar to the private address space in IPv4. This address space is intended to have the same scope as global address but that equates to an enterprise environment. Unique local addresses are assigned from the prefix FD00::/8, using a self-assigned Global ID, where the Local bit is set to 1. The Global ID is not certain to be unique, and there is no form of address registration. Packets with these addresses in the source or destination fields are not intended to be routed in the public Internet, but are intended to be routed in a site. The address prefix FC00::/8 , with the local bit set to 0, is currently undefined.
A former standard proposed the use of “site-local” addresses in the fec0::/10 range, but due to concerns about scalability and the poor definition of what constitutes a site, its use has been deprecated since September 2004
Unicast Considerations
Global Unicast Address Considerations
No significant considerations are necessary if the organization has an address space assignment and a single prefix is deployed.
A multi-homed site may deploy addresses from two or more Service Provider assigned IPv6 address ranges. Here, the network Administrator must have awareness on where and how these ranges are used on the multi-homed infrastructure environment.
The nature of the usage of multiple prefixes may depend on the reason for multi-homing (e.g. resilience failover, load balancing, policy-based routing, or multi-homing during an IPv6 renumbering event)
IPv6 introduces improved support for multi-addressed hosts through the IPv6 default address selection methods.
A multi-homed host may thus have two addresses, one per prefix (provider), and select source and destination addresses.
However multi-homing also has some operative and administrative burdens besides choosing multiple addresses per interface
Local Link Addresses Considerations
Link-Local addresses are designed to be used for addressing on a single link
Generally for the purposes of automatic address configuration, neighbor discovery, or when no routers are present.
Routers should not forward any packets with Link-Local source or destination addresses to other links.
unique only on one physical link
never routed even within particular organization
not globally unique
not unique even within particular organization
used for special features of IPv6 like auto configuration
Unique Local Addresses Considerations
Advantages
Provides Local IPv6 prefixes that can be used independently of any provider-based IPv6 unicast address allocations. This is useful for sites that are not always connected to the Internet or sites that wish to have a distinct prefix that can be used to localize traffic inside of the site.
Applications can treat these addresses in the same manner as any other type of global IPv6 unicast addresses.
Sites can be merged without renumbering of the Local IPv6 addresses.
Sites can change their provider-based IPv6 unicast address without disrupting any communication within the Local IPv6 addresses.
Has a well known prefix that allows for easy filtering at site boundary.
Can be used for in-site Virtual Private Networks.
If accidently leaked outside of a site via routing or DNS, there is no conflict with other addresses.
Disadvantages
It is not possible to route Local IPv6 prefixes on the global Internet. Consequentially, it is necessary to have the default behaviour of site border routers to filter these addresses.
There is an extremely low probability of non-unique locally assigned addresses. This risk can be ignored for all practical purposes, but it still leads to a theoretical risk of clashing addresses.
Recommendations
The Unique Local Address format is recommended for several reasons:
Allows networks to be combined or privately interconnected without creating any address conflicts or requiring renumbering of interfaces using these prefixes
If accidentally leaked outside of a network via routing or DNS, there is no conflict with any other addresses
ISP independent and can be used for communications inside of a network without having any permanent or intermittent Internet connectivity
Well known prefix to allow for easy filtering at network boundaries
In practice, applications may treat these addresses like global scoped addresses
is designed for Addressing isolated networks
Persistent local-context addresses (independent of provider-based addresses)
VPN (Virtual Private Network) – styled interconnection of local network contexts
Private addresses in terms of routing scope
Global addresses in terms of uniqueness
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