In
computer networking, upstream server refers to a
server that provides service to another server. In other words, upstream server is a server that is located higher in a
hierarchy
A hierarchy (from Greek: , from , 'president of sacred rites') is an arrangement of items (objects, names, values, categories, etc.) that are represented as being "above", "below", or "at the same level as" one another. Hierarchy is an important ...
of servers. The highest server in the hierarchy is sometimes called the origin server—the
application server
An application server is a server that hosts applications or software that delivers a business application through a communication protocol.
An application server framework is a service layer model. It includes software components available to a ...
on which a given
resource resides or is to be created.
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 or
hierarchical network topologies, as packets can be transferred both ways.
For example, in the
domain name system, a
name server in a company's
local area network often forwards requests to the
internet service provider's (ISP's) name servers, instead of resolving the domain name directly — 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 — 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 hierarchy.
References
Network management
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