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A method for establishing symmetric end-to-end connections between IPv6 devices through an IPv4 home router Disclosure Number: IPCOM000012223D
Publication Date: 2003-Apr-18

Publishing Venue

The Prior Art Database



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A method for establishing symmetric end-to-end connections between IPv6 devices through an IPv4 home router


This invention describes a method that enables IPv6 nodes residing either on Internet or a private (home) IP network to set-up symmetric end-to-end connections with another IPv6 node located behind an IPv4 NAT router in another home. The symmetry of the end-to-end connections, i.e. both outgoing as well as incoming connections are possible, is one of the most important requirements for proper functioning of peer-to-peer applications like A/V conferencing, IP telephony and multi-users gaming. The conventional IPv4 NAT routers preclude this symmetry and therefore are a serious obstacle for peer-to-peer applications. To preserve the symmetry of an end-to-end connection between IPv6 nodes that passes through an IPv4 NAT router and in particular to make the incoming connection possible a special method should be applied. This method is worked out in this disclosure. It adds an enhanced feature to the existing IPv4-only routers, namely enabling them to forward the incoming IPv6 packets encapsulated into IPv4 ones to the correct IPv6 node located behind the IPv4-only router. This is done by adding an extra rule in the router's NAT table making the forwarding of the incoming packet possible.

Abbreviations ALG Application Level Gateways API Application Programming Interface A/V Audio/Video
FP Format Prefix
FTP File Transfer Protocol
HTTP Hyper Text Transfer Protocol IANA Internet Assigned Numbers Authority Interface ID Interface Identifier
IPv4, IPv6 Internet Protocol version 4 or 6
ISP Internet Server Provider

LAN Local Area Network NA(P)T Network Address (Port) Translation NLA ID Next-Level Aggregation Identifier RFC Request for Comments
RG Residential Gateway
SLA ID Site-Level Aggregation Identifier TLA ID Top-Level Aggregation Identifier TCP Transmission Control Protocol UDP User Datagram Protocol
WAN Wide Area Network


The terminology used in this disclosure has gained acceptance in the last years and has been used in many RFCs and documents following the original documents.

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General node1 A device that implements either IPv4 or IPv6 or both in its network protocol stack. router A node that forwards IP packets not explicitly addressed to itself.
host Any node that is not a router.
link A communication facility or medium over which nodes can communicate at the link layer,

i.e., the layer below IP. Examples are Ethernets (simple or bridged); PPP links; or ATM networks;
neighbors Nodes attached to the same link.
interface A node's attachment to a link.
address An IP-layer identifier for an interface or a set of interfaces.
packet An IP header plus payload.

Type of nodes IPv4-only node A host or a router that implements only IPv4 and does not understand IPv6. IPv6-only node A host or a router that implements only IPv6 and does not understand IPv4. IPv6/IPv4 node A host or a router that implements bot...