OSF DCE Administration Guide--Core Components

OSF DCE Administration Guide—Core Components
places the server identification information along with the current endpoint in the
host’s endpoint map.
2. The dictionary server then advertises its availability to clients by placing
(exporting) its host name (usually it’s the host address) and the transport it uses to
a server entry in CDS.
3. When the dictionary client makes a call to a remote procedure provided by the
server, the DCE software on the client queries the CDS server to find the
dictionary server’s host name and the transport.
4. The client system’s host software then queries the endpoint map on host curly to
find the dictionary server’s endpoint (port 1015).
5. Equipped with all the necessary binding information, the host services on host
larry transmit the remote procedure call directly to port 1015 on host curly.
Although we’ve omitted some details in this high-level example, the figure still shows
the major binding activities performed by clients and servers. That is, servers place their
binding information in CDS and in the host endpoint map where clients look for it.
There are other ways for clients to find servers and there are variations on the mechanism
we’ve described. But these alternatives are generally controlled by the applications
themselves rather than through conventional DCE administration facilities like dcecp.
This section discussed one basic client/server binding mechanism. The following
sections examine the roles played by the endpoint map and by CDS. We’ll also discuss
specific administration tasks for managing binding information in endpoint maps and in
CDS.
10.3 Using the Endpoint Map for Easy Application
Development and Administration
Remote clients can find a server by using the server host’s endpoint map to determine the
server’s communication endpoint. But how do remote clients know where to find the
endpoint map itself? They know because the endpoint map is always accessible at a
well-known endpoint (that is, it is always the same endpoint) on each host so clients can
easily find it.
When hosts support multiple transports, the endpoint map listens on one port for each
transport. In the IP address family (both TCP and UDP), the endpoint map process
listens on port 135. In the Domain Domain Sockets (DDS) address family, it listens on
port 12. In the DECnet NSP address family, it listens on port 69. A complete list of the
protocol sequences and well-known endpoints used by the endpoint mapper service can
be found in the header file /opt/dcelocal/share/include/dce/ep.idl.
Note that not all hosts support all transports. DCE software tries to ensure that at least
one transport is shared between a client and a server.
While well-known endpoints provide convenient access to some critical servers, for most
servers they are impractical. That’s because some address families have a limited
number of endpoints and well-known endpoints can be assigned only by a central
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