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In the early Internet, address prefixes were not allocated to create a summarizable, hierarchical routing infrastructure. Instead, individual address prefixes were assigned and each address prefix became a new route in the routing tables of the Internet backbone routers. Today’s Internet is a mixture of flat and hierarchical routing, but there are still more than 85,000 routes in the routing tables of Internet backbone routers.
IPv4 must be configured, either manually or through the Dynamic Host Configuration Protocol (DHCP). DHCP allows IPv4 configuration administration to scale to large networks, but you must also configure and manage a DHCP infrastructure.
Mobility is a new requirement for Internet-connected devices, in which a node can change its address as it changes its physical attachment to the Internet and still maintain existing connections. Although there is a specification for IPv4 mobility, due to a lack of infrastructure, communications with an IPv4 mobile node are inefficient.
IPv6 hosts can automatically configure their own IPv6 addresses and other configuration parameters, even in the absence of an address configuration infrastructure such as DHCP.
Unlike IPv4, IPv6 support for IPsec protocol headers is required. Applications can always rely on industry standard security services for data sent and received. However, the requirement to process IPsec headers does not make IPv6 inherently more secure. IPv6 packets are not required to be protected with Authentication Header (AH) or Encapsulating Security Payload (ESP). For more information about IPsec, AH, and ESP, see Chapter 18, “Internet Protocol Security (IPsec).”
IPv6 has an equivalent to the IPv4 TOS field that has a single interpretation for nonstandard delivery. Additionally, a Flow Label field in the IPv6 header indicates the packet flow, making the determination of forwarding for nondefault delivery services more efficient at intermediate routers.
Rather than attempting to add mobility to an established protocol with an established infrastructure (as with IPv4), IPv6 can support mobility more efficiently.
With such a large address space, expressing an individual IPv6 address became problematic.The designers of IPv6 settled on colon-hexadecimal notation, which divides the 128-bit address into eight 16-bit blocks separated by colons. Each 16-bit block is expressed in hexadecimal format (rather than decimal format for IPv4). The result is the IPv6 address.
IPv6 defines three types of addresses: unicast, multicast, and anycast. Unicast and multicast addresses work in the same way as they do for IPv4. An anycast address, however, is a strange mixture of unicast and multicast. Whereas a unicast address is used for one-to-one delivery and a multicast address is used for one-to-many delivery, an anycast address is used for one-to one- of-many delivery.
Global addresses are the equivalent of IPv4 public addresses. Global addresses are globally reachable on the IPv6 Internet. Unlike public IPv4 address prefixes, which are a combination of flat and summarizable address spaces, IPv6 global addresses are easier to aggregate and summarize at address space boundaries. This results in fewer routes in the various routing domains of the Internet.
Link-local addresses, which are used on the same link, are equivalent to Automatic Private IP Addressing (APIPA) IPv4 addresses used by current Microsoft desktop and server operating systems. Link-local addresses are automatically configured and can be used to provide automatic addressing for nodes connected to the same network segment when there is no router present. Link-local addresses always begin with “FE80”.
Unique local addresses are defined to be used within the sites of an organization but not on the IPv6 Internet. Unique local addresses are roughly equivalent to private IPv4 addresses except that part of a unique local address prefix is randomly generated to prevent address duplication between sites of an organization and between organizations. Unique local
addresses begin with “FD” or “FC”.
To resolve domain names to IPv6 addresses, RFC 1886 defines the use of the AAAA (or quad-A) Domain Name System (DNS) resource record to resolve a DNS name to an IPv6 address. The AAAA record is analogous to the address (A) record that exists for resolving a DNS name to an IPv4 address. To obtain an AAAA record in a DNS query response, a querying host must specify either AAAA records or all records in its DNS query.
(fully expressed as
the name in the reverse domain namespace Is 1.D.7.4.F.5.E.F.F.F.0.0.A.A.2.0.D.C.188.8.131.52.0.0.8.B.D.0.1.0.0.2.IP6.ARPA.
The IPv6 header is described in RFC 2460. It has a new, streamlined design that removes unneeded fields and moves seldom-used fields to extension headers. Even with addresses that are four times larger than IPv4 addresses, the size of the IPv6 header is only twice as large as the IPv4 header, with a 40-byte fixed size. Although larger, the IPv6 header contains fewer fields and is more efficiently processed by routers. Like IPv4, IPv6 is connectionless and provides a best-effort delivery to the destination.
MLD, defined in RFC 2710, is the IPv6 equivalent to Internet Group Management Protocol (IGMP) version 2 for IPv4. MLD defines ICMPv6 messages that are used by hosts to register group membership, by hosts to leave a group, and by routers to query the subnet for group