APPC/5250 Hot Backup Fails if Configured for "On Demand" (139898)

SYMPTOMS

A 5250 emulator that loses the AS/400 session due to a connection outage on a SNA Server gets the following error when you try to reestablish a session with the AS/400:

The connection to the AS/400 cannot be activated.

Primary Return Code = 0003
Secondary Return Code = 00000004

CAUSE

When SNA Server is configured to use a default Local APPC LU, the hot backup function for APPC/5250 does not give a Remote LU on a disabled connection a lower priority than a Remote LU on an Inactive connection which causes hot backup to fail. If only one of the connections is "Active" and it fails, the other "On Demand" connections still have a lower priority than the previously Active connection that has since failed. Since this failed connection still has the higher priority, none of the On Demand connections are activated. Therefore, hot backup fails and the 5250 emulator reports the error above.

RESOLUTION

Microsoft has updated the following files to correct this problem:

Source files affected:

\DCL\S1SRC\SLPRCHLU.C

Binaries affected:

<snaroot>\SYSTEM\SNASERVR.EXE
<snaroot>\SYSTEM\TRCSERVR.EXE

To work around this problem, SNA Servers that provide hot backup for APPC/5250 sessions can have their AS/400 connections configured for "On Server Startup" activation.

STATUS

Microsoft has confirmed this to be a problem in SNA Server for Windows NT. This problem was corrected in the latest SNA Server for Windows NT, 2.11 U.S. Service Pack. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

MORE INFORMATION

If there are two or more SNA Servers in a domain that are configured to provide Hot Backup for APPC/5250 sessions and those SNA Servers have connections to an AS/400 that have a status of On Demand when viewed in SNA Server Admin, the first 5250 emulator to request a session with the AS/400 forces one of these On Demand connections to become Active.

Subsequent 5250 sessions now use this Active connection to gain access to the AS/400. If this Active connection fails, 5250 users that attempt to reconnect to the AS/400 fail with the error described in the symptom section.

If more than one of the SNA Servers in the domain have an Active connection to the AS/400, 5250 users are able to reconnect to the AS/400 even if the connection on the SNA Server that they were originally communicating through fails.

For additional information on how to configure SNA Servers for hot backup and load balancing, please see the following article in the Microsoft Knowledge Base:

128244 SNA Server Load Balancing and Hot Backup