Visibility of SQL Server and Comm Server to Their Clients (65012)

SUMMARY

Question:

How does an OS/2 LAN Manager workstation know which OS/2 LAN Manager servers are running the SQL Server service? Also, how does an OS/2 LAN Manager workstation know which OS/2 LAN Manager servers are running Communications Server clients?

Response:

If SRVHIDDEN in the LANMAN.INI file is set to no, OS/2 LAN Manager servers announce their presence by periodically broadcasting a mailslot which is referred to as a "server announce packet." The rate of broadcasts can be controlled using the SRVANNOUNCE parameter. When SQL Server is running, an additional bit is set in this announce packet to indicate its presence.

All OS/2 LAN Manager workstations listen for server announce packets from their primary (DOMAIN=) and secondary (OTHDOMAINS=) domains and build their list of servers from the packets they receive. This is the list you see when you run a NET ADMIN or NET VIEW command.

The SQL Server SAF program maintains its own list of SQL servers by looking for the announce packets that have the SQL Server presence bit set. Please note, however, that SAF will only build a list of known SQL Servers from the primary and secondary domains (since those are the only announce packets picked up by the workstation). Despite this, it is still possible to connect to a SQL Server by specifying the name explicitly (as opposed to selecting it from the list box of known SQL Servers).

Communications Server (CS) version 1.00 does not use LAN Manager server announce packets to indicate the presence of a CS server, but instead sends its own special broadcast mailslot messages to clients. For CS 1.00, clients only listen for CS computers that reside on the primary workstation domain. In other words, they can only connect to CS server computers that reside on the same primary domain.