OSF DCE Administration Guide--Core Components

OSF DCE Administration Guide—Core Components
exist in the clerk’s cache, the clerk must know of at least one CDS server to contact in
search of the name.
The clerk can learn about CDS servers and their locations in any of three ways:
• Through the solicitation and advertisement protocol
• During a regular lookup
• By response to the cdscache create command
13.2.1 The Solicitation and Advertisement Protocol
Clerks and servers on the same LAN communicate by using the solicitation and
advertisement protocol. A server broadcasts messages at regular intervals to advertise its
existence to clerks on its LAN. The advertisement message contains data about the cell
that the server belongs to, the server’s network address, and the clearinghouse it
manages. Clerks learn about servers by listening for these advertisements on the LAN.
A clerk also sends out solicitation messages that request advertisements at startup.
13.2.2 Lookups
During a lookup, if a clearinghouse does not contain a name that the clerk is searching
for, the server managing that clearinghouse gives the clerk as much data as it can about
where else to search for the name. If a clearinghouse contains replicas that are part of the
full name being looked up, but not the replica containing the target simple name, it
returns data from a relevant child pointer in the replica it does have. The data helps the
clerk find the next child directory in the path toward the target simple name. The child
pointer’s CDS_Replicas attribute contains this data, in the form of clearinghouse names
and binding information.
13.2.3 The cdscache create Command
A DCE administrator can run the dcecp cdscache create command to create knowledge
in the clerk’s cache about a server. This command is useful when the server and clerk
are separated by a wide area network (WAN), and the clerk therefore cannot learn about
the server from advertisements on a LAN.
Figure 13-5 is an example of how the clerk works downward from the root of the cell
namespace to locate an object entry. The object entry, /.:/Sales/Spell, describes a spell-
checking server at a company’s London sales headquarters.
Figure 13-5. How the Clerk Finds a Name
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