HP-UX IP Address and Client Management Administrator's Guide HP-UX 11i v2, HP-UX 11i v3

Dynamic Service Tracking
When service instances like printers or fax machines are added to a network, they are quickly
visible to clients. When they are removed from the network, they are no longer visible to the
clients. You can describe a service by configuring values for the attributes that are possible for
that service. Clients can detect the entry and exit of services faster.
For example, you can describe a printer as a PostScript® printer, a printer that has blue paper
available, or a printer on the same floor as the user’s office. You can track a service by specifying
the values of the attributes if services are replaced or removed from the network; user agents
discover alternate or replicated servers and continue to operate.
Ease of Administration
You do not need to configure clients to find new services or to remove services when they are
no longer available.
Ease of Development
SLP’s well-defined APIs and protocol semantics allow service developers to rapidly provide
network services.
SLP Components
The SLP framework comprises the following agents and processes:
User Agent
The User Agent (UA) issues a service request on behalf of the client application, specifying the
characteristics of the service that the client requires. The user agent can directly issue a multicast
request to Service Agents.
Service Agent
The Service Agent (SA) works on behalf of one or more services to advertise the service on the
network. Service agents advertise their service through service agent advertisements. In the
absence of Directory Agents (DAs), the SA responds to multicast requests sent by the User Agents.
If a DA is available, the SA registers and, optionally, withdraws services with DAs that support
its scopes. All the network services are grouped together by using scopes that indicate a particular
location, administrative grouping, and proximity in a network topology or any other category.
For more information about scopes, see “Assigning Scopes” (page 58).
The HP-UX implementation of SLP includes a Service Agent Server, with which the services
register their service information. Therefore, instead of having multiple individual Service Agents
running on a host, there is only one Service Agent Server advertising multiple services.
Directory Agent
The Directory Agent (DA) is an optional SLP agent that maintains a cache of service
advertisements sent by the SA. The DA provides this information to the clients that are trying
to discover the services. A DA sends periodic unsolicited advertisements through which SAs
and UAs discover the DA within shared scopes.
UDP and Multicast Ports
SLP uses UDP and multicast ports in the following scenarios:
SLP Overview 53