IPv6 Unicast Local Use Addresses: Link-Local and Site-Local Addresses in Software

Generating Code 3 of 9 in Software IPv6 Unicast Local Use Addresses: Link-Local and Site-Local Addresses

For local use, IPv6 provides both link-local and site-local addresses Link-local addressing is used for interfaces (hosts) that are physically connected to a network This is usually a small local network A link-local address uses only three fields, the format prefix FE8 (10 bits), an empty field (54 bits), and the interface identifier (host address, 64 bits) In effect, the network section is empty IPv6 site-local addresses have three fields: the format prefix (10 bits), the subnet identifier (54 bits), and the interface identifier (64 bits) Except for any local subnetting, there is no network address

Multicast addresses have a format prefix of FF (8 bits) with flag and scope fields to indicate whether the multicast group is permanent or temporary and whether it is local or global in scope A group identifier (112 bits) references the multicast group For the scope, 2 is linklocal, 5 is site-local, and E is global In addition to their interface identifiers, hosts will also have a group ID that can be used as a broadcast address You use this address to broadcast to the hosts The following example will broadcast only to those hosts on the local network (5) with the group ID 101:

FF05:0:0:0:0:0:0:101

To broadcast to all the hosts in a link-local scope, you would use the broadcast address:

FF02:0:0:0:0:0:0:1

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FF05:0:0:0:0:0:0:2

In the transition from IPv4 to IPv6, many networks will find the need to support both Some will be connected to networks that use the contrary protocol, and others will have to connect through other network connections that use that protocol There are several official IETF methods for providing IPv6 and IPv4 cooperation, which fall into three main categories:

Dual-stack Allows IPv4 and IPv6 to coexist on the same networks Translation Enables IPv6 devices to communicate with IPv4 devices Tunneling Allows transmission from one IPv6 network to another through IPv4 networks, as well as allowing IPv6 hosts to operate on or through IPv4 networks In the dual-stack methods, both IPv6 and IPv4 addresses are supported on the network Applications and DNS servers can use either to transmit data Translation uses NAT tables (see 20) to translate IPv6 addresses to corresponding IPv4 addresses and vice versa as needed IPv4 applications can then freely interact with IPv6 applications IPv6-to-IPv6 transmissions are passed directly through, enabling full IPv6 functionality Tunneling is used when one IPv6 network needs to transmit to another through an IPv4 network that cannot handle IPv6 addresses With tunneling, the IPv6 packet is encapsulated within an IPv4 packet, where the IPv4 network then uses the outer IPv4 addressing to pass on the packet Several methods are used for tunneling, as shown here, as well as direct manual manipulation: 6-over-4 Used within a network to use IPv4 multicasting to implement a virtual LAN to support IPv6 hosts, without an IPv6 router (RFC 2529) 6-to-4 Used to allow IPv6 networks to connect to and through a larger IPv4 network (the Internet), using the IPv4 network address as an IPv6 network prefix (RFC 3056) Tunnel brokers Web-based services that create tunnels (RFC 3053)

A set of configuration files in the /etc directory, shown in Table 34-6, is used to set up and manage your TCP/IP network These configuration files specify such network information as host and domain names, IP addresses, and interface options The IP addresses and domain names of other Internet hosts you want to access are entered in these files If you configured your network during installation, you can already find that information in these files

Without the unique IP address the TCP/IP network uses to identify computers, a particular computer cannot be located Because IP addresses are difficult to use or remember, domain names are used instead For each IP address, a domain name exists When you use a domain

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