At present as broadcast technology definition is not clear, but terminal host through a router is based on packet drawer by decision. As the concept of broadcast technology is not confined to the network layer, it also can realize in other layers (e.g., application layer), the network layer and application layer as sowing techniques are advantages and disadvantages. According to RFC2526 (Anycast so Reserved IPv6 Subnet, March 1993), ren unicast address is "IPv6 retained by the address, assigned to one or more may belong to different physical node of the network interface. Its attribute for sending whomsoever unicast address data of each according to routing protocol distance method, by routing to have the address of the recent interface." Another characteristic is, ren unicast address with conventional unicast address similar. To send data packet unicast address the node does not need to know it is unicast address.
Anycasting was first put forward in the RFC1546 and defined, its original semantic is, in IP network through a Anycast address identifier a group of the provision of the specified services host, and service access party did not care about providing service to what's the exact a host (such as DNS or mirror service), visit this address message can be IP network routing to this group of target of any host computer, it offer is a stateless, best service.
In RFCl546 (Host Anycasting Service, in November 1993), this paper discusses the purpose of any sowing, But then have not developed IPv6 addressing. Reason is the client need two or more servers the services provided. Client does not mind which server providing services, it is important to make the client search services more easily. For example, the customer can type the request, and is connected to recent server, without from information server list choice. Any sowing also provide fault-tolerant, for if a server malfunction, server group of other server can provide services.
RFC2373 (IP Addressing Architecture, six pages July 1998) provides a relatively new instructions and motivation: term unicast address of an expected application is marking belong to a provide Internet service router set. This address can be used as IPv6 routing of the title of the intermediate address, make data packet through an aggregate or polymerization sequence relay. Other possible USES is mark belongs to a subnet router group or provide access to a routing range entry router group.
RFC2373 standard for any sowing is defined as a unicast address was assigned to more than one interface, the interface of the message was sent by routing protocol network routing to measure of "recently" target interface. With Unicast and Multicast similar, Anycast also IP network a communication mode. Unicast allow source node to a single goal node to send data submitted Multicast allow source node, to a group of goal node, and send data submitted to Anycast allows source node to a group of goal node of a node to send data reported, and the node by routing system choice, for source node transparent; Meanwhile, routing system choice "recently" node is the source node, thus providing services in certain procedures for source node provides a better service is alleviated the network load.
At present, the arbitrary point transmission address only used to target address, and only assigned to router. Arbitrary point transmission address from single point transmit address space distribution among the, using a single point of a transmission address format. Ren unicast address structure is shown in figure 1 shows.
Subnet - router arbitrary point transmission address must pass a predefined, this address prefix from subnet produce. For constructing a subnet - router arbitrary point transmission address, subnet prefix must be fixed, the rest of the digits buy for all "0". A subnet within all the router interface were assigned the subnet subnet - router arbitrary point transmission address. Subnet - router arbitrary point transmission address for a group of routers a and remote subnet communications.
Responsible for any, there are unicast address the longest address prefix P, it was limited a topological area, all belong to this as unicast address interface are in this area. In P are conditioned this area, belong to the ren unicast address set of each member must find the classics system as a separate entrance and advertising, In this regions outside, this let unicast address on this might be gathered to prefix P for the advertising.
Any unicast address a topological area, belong to this as unicast address all members are located in them. In this area, each member must be a routing system of an independent study released, but in areas outside, these members as a single coherent as unicast address exist.
RFC1546 discusses some potential problems. For example, IP is without borders and has no record of earlier data submitted to where was passed. If the client to send any unicast address two data reported, a may send to a server, while another may be sent to another server. If you want to ensure that the selected as sowing server, all future data packet are transmitted to the server, need to have a mechanism. Any sowing data submitted to and may be sent to serve the ren unicast address for all the host. In view of these problems, the RFC provides a correct any sowing IP definition, namely "to serve as unicast address of at least one host, it is best to provide a mainframe as sowing data report without borders best effect relay services.
RFC think solution is, in the first data submitted to exchange in understanding the client address and used in the all later dialogue, requests the application procedure keep fit. Relevant as sowing addressing and its system structure, in the application of use, safety consideration and other details of the RFC2526 provides more about how to achieve any sowing IPv6 together the latest proposals.
Ren broadcast communication mode characteristic, making it the IP network is certain to program application prospect. First, the distribution of service share the same IP address, at the same time in the IP layer transparent service orientation, this makes the various network service especially application-layer service has stronger transparency, such as DNS, it can IPv6 network in sharing a known as the IP address, users don't need special configuration also didn't care what a visit DNS server, Secondly, routing system chose "recently" service, shorten service response time, and reduce the network load, Finally, the same service on the network redundancy distribution, routing system can provide mechanism choice load relatively light bandwidth is relatively high paths for forwarding message, as they give users brought two advantages:
1) weakened the DOS attack to the user impacts. When any sowing in group a member or a few members is attacked, responsible for packet forwarding router can according to each group of response time to decide which members should be forwarded to the message, so the attacked members with no response, so messages will not be forwarded to there, at the same time, because any sowing provide service access transparency, group is also relatively difficult by DOS attack.
2) weaken the network congestion give users impacts. Ditto the truth, when some of the group as sowing in congested segment, its response time is longer, messages can be forwarded to respond better members there.
Although any sowing in the above aspects has certain advantages, but at present as broadcast application is not as expected. The application layer to the use of any sowing basically has server automatically select, service automatic positioning, server automatically select can use in need of some application-layer services provide multiple mirror servers, such as FTP service, online gaming service, etc. Service automatic positioning can use on the host does not need special configuration and the use of a well-known service of circumstance, typical such as DNS. The network layer realize any sowing are mainly on the basis of any sowing routing table of any messages for transparent forwarding, provide to the upper service, so the application layer will not need special as broadcast program modules. Any sowing routing table records a let all the members of the broadcast group Unicast address, when a router received a pointer to let Unicast address message, the first search any sowing routing table find corresponding any message broadcast group, then put forward to this group of a member. In view of the application layer of worldwide as sowing requirement so contributed to the network layer global research on the mechanism of any sowing.
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