In highly available systems, there can be many instances of a service (for instance an SMB3 file service [MS-SMB2]) running on a server or group of servers. These service instances are accessed by clients through network DNS names and associated IP addresses.
The Service Witness Protocol enables a client application (for instance, an SMB3 client) to receive prompt and explicit notifications about the failure or recovery of a network name and associated services, rather than relying on slower detection mechanisms such as time-outs and keep-alives.
The Service Witness Protocol is an independent protocol which is used alongside other protocols, as illustrated by the following figure.
Figure 1: Witness clients communicating with Witness servers