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About Knowledge References
Deciding Between Referrals and Chaining
Both methods of linking your directory partitions have advantages and
disadvantages. The method, or combination of methods, you choose depends
upon the specific needs of your directory.
The major difference between the two knowledge references is the location of the
intelligence that knows how to locate the distributed information. In a chained
system, the intelligence is implemented in the servers. In a system that uses
referrals, the intelligence is implemented in the client application.
While chaining reduces client complexity, it does so at the cost of increased server
complexity. Chained servers must work with remote servers and send the results
to directory clients.
With referrals, the client must handle locating the referral and collating search
results. However, referrals offer more flexibility for the writers of client
applications and allow developers to provide better feedback to users about the
progress of a distributed directory operation.
The following sections describe some of the more specific differences between
referrals and chaining in greater detail.
Usage Differences
Some client applications do not support referrals. Chaining allows client
applications to communicate with a single server and still access the data stored
on many servers. Sometimes referrals do not work when a company's network
uses proxies. For example, a client application has permissions to speak to only
one server inside a firewall. If they are referred to a different server, they will not
be able to contact it successfully.
Also, with referrals a client must authenticate, meaning that the servers to which
clients are being referred need to contain the client credentials. With chaining,
client authentication takes place only once. Clients do not need to authenticate
again on the servers to which their requests are chained.
Evaluating Access Controls
Chaining evaluates access controls differently from referrals. With referrals, an
entry for the client must exist on all of the target servers. With chaining, the client
entry does not need to be on all of the target servers.
For example, a client sends a search request to server A. The following diagram
illustrates the operation using referrals:
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Netscape Directory Server Deployment Guide • October 2004
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