| 单词 | IPv6 (Internet Protocol version 6) |
| 释义 | IPv6 (Internet Protocol version 6) • Next Header: 8 bits identifying the header immediately following the IPv6 header. Examples include TCP, UDP, Fragment, and Authentication. • Hop Limit: 8 bits that specify the number of hops through which the packet can travel. Each router along the path decrements the field value by one until the value reaches zero, at which point the packet is discarded.This field is similar to the IPv4 TTL (Time To Live) field, with the exception that the seconds parameter has been eliminated and only the hops parameter is supported. • Source Address: 128 bits (hexadecimal) containing the IP address of the source host. • Destination Address: 128 bits (hexadecimal) containing the IP address of the destination host. IPv6 supports multiple extension headers. RFC 1883 recommends that they be placed in the following order: • Hop-by-Hop Options: Optional information that must be examined by every node along a path taken by a packet.This header carries information such as the type of extension header immediately following, and specific instructions as to what should be done if the processing node does not recognize the Option Type, and whether or not the option data may change en route.This header also identifies the length of the Hop-by-Hop header, and contains padding options. • Destinations Options: Optional information that must be examined by the destination host.This header carries information such as the type of header immediately following, the length of the Destination header, and padding options. • Routing: This IPv6 source node uses this header to list one or more intermediate modes to be visited along the path the packet takes to its destination. • Fragment: The IPv6 source node uses this header to send a packet larger than the path MTU will accommodate. All fragmentation occurs at the source node. • Authentication: As defined in RFC 2402, this header contains a mechanism for ensuring the connectionless integrity and data origin authentication of IP datagrams, as well as an anti-replay option. This header might also include a non-repudiation mechanism, which provides the origination node with confirmation of packet receipt. Included in this header may be the authentication algorithm and keys, the encryption algorithm and keys, and other security-related parameters. • Encapsulating Security Payload: As defined in RFC 2406, this header provides confidentiality through encryption, and limited confidentiality of the traffic flow. It also may provide connectionless integrity and data origin authentication of IP datagrams, as well as an anti-replay option. IPsec (IP security) is a standards-based security suite that operates transparently and may eliminate the need for proprietary firewall mechanisms in some applications. IPsec also provides for encapsulation of the secured IPv6 packets inside IPv4 datagrams, in consideration of both the increasing need for security and the long-term transition process to IPv6. IPv6 addressing is considerably enhanced, in comparison to IPv4. Not only is the address space increased to 128 bits, but IPv6 also supports multiple address types, including anycast, multicast, and unicast. IPv6 offers highly flexible address assignment through two approaches. Stateful autoconfiguration dynamically assigns unique addresses to devices as they require them, drawing from a pool of such addresses. Stateless autoconfiguration employs two IP addresses, and is particularly advantageous in mobile applications. One address is assigned permanently to the mobile device, and another address is used to route data to the network to which the mobile device is connected at the time. See also algorithm, anycast, Application Layer, authentication, datagram, encryption, firewall, flow, hop, IETF, IPng, IPsec, IPv4, IPv6 address, jumbo payload, key, MTU, multicast, node, non-repudiation, payload, protocol, QoS, real-time, stateful autoconfiguration, stateless autoconfiguration, TCP, TTL, UDP, and unicast. 74570c09.qxd 9/11/07 12:22 PM Page 257 |
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