The RFC-2782 A DNS RR for specifying the location of services (DNS SRV) specifies a mechanism for requesting the names and rudimentary descriptions for machines that provide network services. The DNS client requests the descriptions for all machines that are registered as offering a particular service name. In this case the service name requested will be “LDAP”. The DNS server may respond with multiple names for a single request.
Figure H.1-3 Find LDAP Server
DNS Server Provides list of LDAP servers
LDAP Client Requests list of LDAP servers
RFC-2181 Clarifications to the DNS Specification
RFC-2219 Use of DNS Aliases for Network Services
RFC-2782 A DNS RR for specifying the location of services (DNS SRV)
other RFC’s are included by reference from RFC-2181, RFC-2219, and RFC-2782.
Figure H.1-4 Select LDAP Server
The DNS client shall request a list of all the LDAP servers available. It will use the priority, capacity, and location information provided by DNS to select a server. (RFC-2782 recommends the proper use of these parameters.) It is possible that there is no LDAP server, or that the DNS server does not support the SRV RR request.
Notes: 1. Multiple LDAP servers providing access to a common replicated LDAP database is a commonly supported configuration. This permits LDAP servers to be located where appropriate for best performance and fault tolerance. The DNS server response information provides guidance for selecting the most appropriate server.
2. There may also be multiple LDAP servers providing different databases. In this situation the client may have to examine several servers to find the one that supports the DICOM configuration database. Similarly a single LDAP server may support multiple base DNs, and the client will need to check each of these DNs to determine which is the DICOM supporting tree.
The client may have a mechanism for manual default selection of the LDAP server to be used if the DNS server does not provide an LDAP server location.