Upstream server
Encyclopedia
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 the hierarchy
of servers. The highest server in the hierarchy is sometimes called the origin server. 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.
Server (computing)
In the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
that provides service to another server. In other words, upstream server is a server that is located higher in the hierarchy
Hierarchy
A hierarchy is an arrangement of items in which the items are represented as being "above," "below," or "at the same level as" one another...
of servers. The highest server in the hierarchy is sometimes called the origin server. 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
Hierarchical routing
Hierarchical routing is method of routing in networks that is based on hierarchical addressing.-Background:Most Transmission Control Protocol/Internet Protocol routing is based on a two-level hierarchical routing in which an IP address is divided into a network portion and a host portion...
or hierarchical network topologies, as packets can be transferred both ways.
For example, in the domain name system
Domain name system
The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
, a name server
Name server
In computing, a name server is a program or computer server that implements a name-service protocol. It maps a human-recognizable identifier to a system-internal, often numeric, identification or addressing component....
in a company's local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
often forwards requests to the internet service provider
Internet service provider
An Internet service provider is a company that provides access to the Internet. Access ISPs directly connect customers to the Internet using copper wires, wireless or fiber-optic connections. Hosting ISPs lease server space for smaller businesses and host other people servers...
'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
Domain name
A domain name is an identification string that defines a realm of administrative autonomy, authority, or control in the Internet. Domain names are formed by the rules and procedures of the Domain Name System ....
hierarchy.