TCP option "request IPv6 connection"

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Last updated 2018-08-15 (latest revision 2018-02-11)
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


This document describes an idea for a header "option" for the Transmission Control Protocol (TCP). The extension is used by dual-stack nodes to force the use of the IPv6 protocol instead of the IPv4 protocol when exchanging data over TCP. Especially if one of the two nodes is a NAT64 or NAT46 router it makes sense not to use IPv4 but IPv6 if both nodes are dual-stack nodes. This document also suggests to declare the usage of such a method mandatory for all nodes that use IPv4 addresses that will be assigned by RIRs in the future. Doing so will make it impossible to (mis-) use IPv4 addresses assigned by RIRs to ISPs for IPv4-only nodes that do not support IPv6.


Martin Rosenau (

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