Transitioning from IPv4 to IPv6 in Java

Creator QR-Code in Java Transitioning from IPv4 to IPv6
572 Transitioning from IPv4 to IPv6
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Now that we have seen the technical details of IPv6, let us consider a very practical matter: how will the public Internet, which is based on IPv4, be transitioned to IPv6 The problem is that while new IPv6capable systems can be made "backwards compatible", ie, can send, route, and receive IPv4 packets, already deployed IPv4-capable systems are not capable of handling IPv6 packets Several options are possible One option would be to declare a "flag day" - a given time and date when all Internet machines would be turned off, be upgraded from IPv4 to IPv6 The last major technology transition (from using NCP to using TCP for reliable transport service) occurred almost 20 years ago Even back then [RFC 801], when the Internet was tiny and still being administered by a small number of "wizards," it was realized the such a flag day was not possible A flag day involving hundreds of millions of machines and millions of network administrators and users is even more unthinkable today [RFC 1993] describes two approaches (which can be used either alone or together) for gradually integrating IPv6 hosts and routers into an IPv4 world (with the long term goal, of course, of having all IPv4 nodes eventually transition to IPv6) Probably the most straightforward way to introduce IPv6-capable nodes is a dual stack approach, where IPv6 nodes also have a complete IPv4 implementation as well Such a node, referred to as IPv6/IPv4 node in [RFC 1993], the ability to send and receive both IPv4 and IPv6 packets When interoperating with an IPv4 node, an IPv6/IPv4 node can use IPv4 packets; when interoperating with an IPv6 node, it can speak IPv6 IPv6/IPv4 nodes must have both IPv6 and IPv4 addresses They must furthermore be able to determine whether another node is IPv6-capable or IPv4-only This problem can be solved using the DNS (see 2), which can return an IPv6 address if the node name being resolved is IPv6 capable, or otherwise return an IPv4 address Of course, if the node issuing the DNS request in only
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IPv6
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IPv4 capable, the DNS returns only an IPv4 address
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Figure 47-3: A dual stack approach
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In the dual stack approach, if either the sender of the receiver is only IPv4-capable, IPv4 packets must be used As a result, it is possible that two IPv6-capable nodes can end, in essence, sending IPv4 packets to each other This is illustrated in Figure 47-3 Suppose node A is IPv6 capable and wants to send an IP packet to node E, which is also IPv6-capable Nodes A and B can exchange an IPv6 packet However, node B must create an IPv4 packet to send to C Certainly, the data field of the IPv6 packet can be copied into the data field of the IPv4 packet and appropriate address mapping can be done However, in performing the conversion from IPv6 to IPv4, there will be IPv6-specific fields in the IPv6 packet (eg, the flow identifier field) that have no counterpart in IPv4 The information is these fields will be lost Thus, even though E and F can exchange IPv6 packets, the arriving IPv4 packets at E from D do not contain all of the fields that were in te original IPv6 packet sent from A An alternative to the dual stack approach, also discussed in [RFC 1993], is known as tunneling Tunneling can solve the problem noted above, allowing, for example, E to receive the IPv6 packet originated by A The basic idea behind tunneling is the following Suppose two IPv6 nodes (eg, B and E in Figure 47-3) want to interoperate using IPv6 packets, but are connected to each other by intervening IPv4 routers We refer to the intervening set of IPv4 routers between two IPv6 routers as a tunnel, as illustrated in Figure 47-4 With tunneling, the IPv6 node on the sending side of the tunnel (e g, B) takes the entire IPv6 packet, and puts it in the data (payload) field of an IPv4 packet This IPv4
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