The information in this article applies to:
- Microsoft SNA Server for Windows NT, versions 2.1, 2.11, and 2.11 SP1
SYMPTOMS
When you open the SNA Server Admin from a backup SNA Server, you might
receive the following error message:
The Primary SNA Server for the domain is not active.
NOTE: The troubleshooting steps described in this article do not apply to
SNA Server 3.0.
An SNA Server 3.0 backup or member configuration server locates the primary
SNA Server by contacting it's name (or IP address) directly, based on the
primary server name entered during SNA Server Setup when the backup or
member server was installed. The primary server name is saved under the
following registry key:
HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Services/SnaBase/
PrimaryServer: REG_SZ:
where either the server name or IP address can be entered. If IP address,
enter in standard notation (for example: 123.45.67.89).
CAUSE
A backup SNA Server tries to open the Com.cfg file on the primary SNA
Server. The backup learns about the location of the primary SNA Server when
it receives a broadcast mailslot from the primary. The packet looks like
the following:
Src MAC Dst MAC Prot Description Src
Other Addr Dst Other Addr
00AA006B4BE2 *BROADCAST SMB C transact, File = \MAILSLOT\SNADMOD
157.57.15.231 157.57.15.255 IP
However, when there is an IP router in between the backup and primary SNA
Server, the SNA Server domain must be configured to send directed mailslots
instead of broadcasts.
WORKAROUND
The following outlines how to configure the SNA Server domain to send
directed mailslots instead of broadcasts:
- In SNA Server Admin, click Server Broadcasts on the Options menu.
NOTE: When changes are made to this dialog box, it effects all SNA
Servers in the respective domain.
- Select the Microsoft Networking and Route Server Broadcasts Over IP
Routers check boxes.
- Close the dialog box.
- Save the configuration.
NOTE: You must stop and start the SNABASE service for these changes
to take effect.
MORE INFORMATION
After you make the above changes, the following is a sample packet sent
from the primary to the backup SNA Server.
Notes:
- The destination address is not broadcast, but instead, a specific MAC
address is used.
- The MAC address will be the router's MAC address if the destination
server is on a different segment, but the destination IP address will
be the backup SNA server's IP address.
Src MAC Dst MAC Prot Description Src
Other Addr Dst Other Addr
00AA006B4BE2 08002B314A12 SMB C transact, File = \MAILSLOT\SNADMOD
157.57.15.231 157.57.13.12 IP
When configured this way, the SNA Server relies on the netlogon service of
Microsoft Windows NT to retrieve a list of all domain controllers
participating in the domain. The SNA Server will send a directed mailslot
to each domain controller even if is not running SNA Server.
There are two common methods that the Windows NT netlogon service uses to
retrieve a list of all the servers in the Windows NT domain:
- Queries WINS
WINS must have a registration for each computer acting as a domain
controller. The WINS server's database should have an entry for the
domain_name followed by [1Ch]. If you double-click this entry you should
see a list of all the domain controllers registered with this WINS
server. If the SNA Server is not in this list, the Windows NT computer
has not properly registered with the WINS server as a domain controller.
If your Windows NT domain has 25 or more domain controllers, and you use
WINS for name resolution, the SNA server announcements may not be sent
to all of the SNA Servers. WINS only keeps a list of 25 domain
controllers in the [1Ch] group name. As new backup domain controllers
register, they replace a backup domain controller entry in the list. In
this case you would need to add LMHOSTS files on the SNA servers or use
SNA subdomains.
- Uses local name cache via LMHOSTS with the #PRE #DOM switches.
LMHOSTS file must have an entry for every domain controller with the
extensions #PRE #DOM:domain. An example of this file can be found in
<winntroot>\System32\Drivers\Etc\Lmhosts.sam.
To reload the LMHOSTS file, use the following command:
nbtstat -r
To verify these entries have been properly cached use the following
command:
nbtstat -c
The following are other things to check:
- The SNA Servers must be installed on a domain controller, either a
backup or primary, in the same Windows NT domain. It is not sufficient
to install on a Windows NT Server Non-domain controller.
- From the primary SNA Server, using PING, confirm that the IP address of
each SNA Server is reachable.
NOTE: Using PING to resolve the server's name is not relevant, the
packet does not use the server's netbios name.
- Ensure that the netlogon service on all SNA Servers in the domain is
started.
- If the SNA Server communication is still failing after you check all of
the above, network traces of the traffic from the SNA Server should be
done to capture the server announcements. These will appear as SMBs,
with the following description:
C transact, File = \MAILSLOT\SNADMOD.
The traces can be used to verify the announcements are being generated
and sent to the correct IP addresses. Traces can also be captured on the
other side of the router to verify the messages are arriving on that
segment.
- Try reloading the Netbios name cache on the Windows NT computer where
the Primary SNA Server is running:
nbtstat -R
This will cause the name cache to be purged and reloaded.
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