Branch servers that use DLS use dynamic port for SnaBase connection (276446)


The information in this article applies to:

  • Microsoft Host Integration Server 2000
  • Microsoft SNA Server 3.0 SP1
  • Microsoft SNA Server 3.0 SP2
  • Microsoft SNA Server 3.0 SP3
  • Microsoft SNA Server 3.0 SP4
  • Microsoft SNA Server 4.0
  • Microsoft SNA Server 4.0 SP1
  • Microsoft SNA Server 4.0 SP2
  • Microsoft SNA Server 4.0 SP3
This article was previously published under Q276446

SUMMARY

Branch-based SNA Servers that use a Remote Link Service may not be able to communicate with a central SNA Server if Internet firewalls or screening routers between the SNA Server systems are filtering outgoing Transfer Control Protocol/Internet Protocol (TCP/IP) ports in addition to incoming TCP/IP ports.

Branch-based SNA Servers open a connection to a central SNA Server's SnaBase service in order to initialize the distributed host connection. The TCP/IP source port that is used by the branch server for this SnaBase connection is dynamic. If there is a firewall or screening router between the branch and central SNA Server that is filtering on outgoing ports, the firewall will not forward the responses from the central SNA Server to the branch SNA Server because the "dynamic" source port will not be known to the firewall.

NOTE: In most cases that involve firewalls (or screening routers), only the incoming TCP/IP ports are filtered, so this would not be an issue. The filtering of outgoing TCP/IP ports is not as common as filtering incoming ports.

For additional information about the latest service pack for SNA Server 4.0, click the following article number to view the article in the Microsoft Knowledge Base:

215838 How to obtain the latest SNA Server version 4.0 service pack

MORE INFORMATION

The following Knowledge Base articles describe how to configure SNA Servers to use specific (static) TCP/IP ports and ranges of ports when using Distributed Link Services (DLS) in environments that use firewalls and/or screening routers: For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

164590 Branch servers using DLS cannot communicate through firewalls

After you apply the update, the branch-based SNA Servers that use the methods described by the referenced articles will also use static TCP/IP ports (or a range of static ports) to open connections to a central SNA Server's SnaBase service.

NOTE: A range of ports should be used for the reasons described in the referenced articles.
Modification Type:MinorLast Reviewed:8/20/2004
Keywords:kbinfo kbQFE KB276446 kbAudDeveloper
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