SLP is an advertisement protocol in that it allows services to advertise themselves in response to a broadcast or multicast request for a particular service.
There are three different SLP roles called agents.
|SLP Role (Agent)||Notes|
|Service Agent (SA)||Service wishing to advertise its presence and what it offers. SMI-S servers are required to implement the Service Agent role.|
|User Agent (UA)||Client that wishes to find a service. The storage service implements the role of User Agent.|
|Discovery Agent (DA)||Optional role that allows scaling and use of SLP across subnets. One or more Discovery Agents may be used in your implementation. A Service Agent using OpenSLP can be easily configured to function as both an SA and a DA so you don’t need to install any additional copies of OpenSLP for this role if you already have providers that use OpenSLP (although you could).|
SLP uses UDP multicast and/or broadcasts for requesting advertisements from SAs. This works well when the storage service (the UA looking for services) and the SMI-S providers (SAs advertising services) are all located on the same subnet. Although most network switches and routers can be configured to pass these requests across subnets (particularly multicast), this is not typical in larger organizations.
If your storage service machine is not located on the same subnet as all of your SMI-S providers, the best approach is to select one of the SMI-S provider systems and configure it as a Discovery Agent (DA) in addition to its Service Agent (SA) role.