Inter-server
In computing, inter-server is a technical term used in network protocol design to refer to the extension of the client-server model by having parts of a protocol which are only exchanged between the servers. In some fields server-to-server (S2S) is used as an alternative, and the term inter-domain can in some cases be used interchangeably.
Protocols that have inter-server functions as well as the regular client-server protocols include: DNS, which uses an inter-server protocol for zone transfers; FXP, allowing file transfer directly between FTP servers; IRC, an Internet chat system with an inter-server protocol allowing clients to be distributed across many servers; SIP, a signalling protocol commonly used for Voice over IP; and SILC, a secure Internet conferencing protocol.