The TCP Service Number Option (SNO)

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Last updated 2014-09-05 (latest revision 2014-03-04)
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


This document specifies a TCP option for service numbers. The current SYN destination port is used both to indicate the desired service and as a connection demultiplexing field. This option separates those two functions, retaining the current destination port solely for demultiplexing and indicating the service separately in a service number option (SNO). By decoupling these two functions, SNO allows a larger number of concurrent connections for a single service, as might be useful between fixed addresses of proxies.


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