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

• SLP uses multicast ports for discovering Directory Agents and for issuing requests to Service
Agents by default.
• SLP listens on port 427.
• SLP uses UDP for service request messages by the User Agents. However, in the following
cases, a TCP connection is required:
— The User Agent issues requests larger than the path MTU (largest packet size when
communicating with a remote machine).
— The Service Agent sends replies larger than the path MTU, and User Agents are not
configured to accept the replies with the OVERFLOW flag set (this flag enables the UA
to only make use of the truncated reply or to reformulate the request to limit the reply).
— Directory Agents must be able to respond to UDP and TCP requests.
SLP Architecture
The SLP architecture, at its most basic level, includes the following players in a typical service
location problem:
• A client or user that is searching for a service to satisfy particular requirements or that
requires information on the characteristics of a particular service.
• A server or service provider that is advertising a service having particular characteristics.
At the simplest level, an architecture for service location must provide a way for the UA to obtain
a set of services having particular characteristics from SAs advertising those services. The
information provided by SAs describing services is called a service advertisement.
A service advertisement is a URL and a collection of attribute-list pairs that describe a service.
All service advertisements have a valid lifetime. Upon expiry of this lifetime, the service
advertisements become invalid, unless they are reregistered.
Service advertisements characterize an instance of a service through a collection of attributes
that describe the service. One of those attributes is the type of service being offered, known as
the service type. The service type attribute describes a class of services that share the same
attributes. It also includes information about what protocol clients must use when contacting
the service.
The service advertisement also contains another important piece of information: the service
access point, which helps the UA to access the service. Normally, the service access point
encapsulates the machine’s host name or IP address and perhaps a port number.
Figure 1-6 illustrates SLP architecture for a network.
54 Overview