# Upstream server

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{{More citations needed|date=February 2022}}

In [computer networking](/source/computer_networking), '''upstream server''' refers to a [server](/source/server_(computing)) that provides service to another server. In other words, upstream server is a server that is located higher in a [hierarchy](/source/hierarchy) of servers. The highest server in the hierarchy is sometimes called the '''origin server'''—the [application server](/source/application_server) on which a given [resource](/source/System_resource) resides or is to be created.<ref>{{cite IETF|title= Hypertext Transfer Protocol -- HTTP/1.1|page=9|rfc=2616|author1= R. Fielding|author2= J. Gettys|author3=J. Mogul|doi=10.17487/RFC2616|url=https://datatracker.ietf.org/doc/html/rfc2616|access-date=11 December 2021|archive-url=https://web.archive.org/web/20211127173010/https://datatracker.ietf.org/doc/html/rfc2616|archive-date=27 November 2021|url-status=live|publisher=[Internet Engineering Task Force](/source/Internet_Engineering_Task_Force)|date= June 1999|location=[United States](/source/United_States)}}</ref> The inverse term, '''downstream server''', is rarely used.

The terms are exclusively used in contexts where requests and responses move in opposite ways. It is not used when discussing [hierarchical routing](/source/hierarchical_routing) or [hierarchical network topologies](/source/network_topology), as packets can be transferred both ways.

For example, in the [domain name system](/source/domain_name_system), a [name server](/source/name_server) in a company's [local area network](/source/local_area_network) often forwards requests to the [internet service provider](/source/internet_service_provider)'s (ISP's) name servers, instead of resolving the domain name directly &mdash; it can be said that the ISP's name servers are '''upstream''' to the local server. Conversely, the ISP's servers typically resolve domain names from the domain's authoritative '''origin servers''' &mdash; the authoritative servers are said to be '''upstream''' to the ISP's servers. Note that the hierarchy of resolvers is unrelated to the actual [domain name](/source/domain_name) hierarchy.

==References==
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Category:Network management

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Adapted from the Wikipedia article [Upstream server](https://en.wikipedia.org/wiki/Upstream_server) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Upstream_server?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.