tailieunhanh - routing8

Tham khảo tài liệu 'routing8', công nghệ thông tin, chứng chỉ quốc tế phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | IPv6 Functionality 689 Renumbering Site renumbering will still occur even with the abundance of IP addresses. Address prefixes are strictly maintained and an address assigned to a site might need to be recalled occasionally. Or the site might want to change ISPs which would require a prefix change just as it does today with IPv4 if a company changes ISPs. IPv6 was not designed to eliminate this phenomenon but it is designed to make renumbering easier. An address is in one of two states preferred or deprecated. A host should always attempt to communicate using a preferred address. A deprecated address should be used only as the source address if using a preferred address will cause an existing connection to be disrupted. If two hosts have a TCP connection established using preferred addresses for example and one host s address changes to deprecated if the host switches to a new preferred address the connection will fail. Host renumbering is simplified by the use of preferred and deprecated addresses. The time that an address remains preferred is set and modified in Router Advertisements which are periodically sent on the link and are processed by every node on the link. New prefixes can be added to the Router Advertisements thus adding new addresses to the interfaces and old ones can be deprecated and removed. A similar mechanism can be used to renumber hosts using a configuration server. The server may multicast a request to all nodes asking them to reconfirm their assigned addresses. The hosts will query the configuration server and obtain addresses with modified lifetime values deprecating existing addresses or assigning new preferred addresses. The robustness of this renumbering mechanism depends on the Router Advertisements and stateful messages reaching all hosts on a link. Consider the following case study taken from RFC 2641. Case Study Renumbering a Network A prefix is advertised with a lifetime of two months. On August 1 it is determined that the prefix .