Connecting Across a Firewall

Set the CommLinks connection parameters in your application's connection string to connect across a firewall.

There are restrictions on connections when the client application is on one side of a firewall and the server is on the other. Firewall software filters network packets according to network port. Also, it is common to disallow UDP packets from crossing the firewall.

When connecting across a firewall, you must use a set of communication parameters in the CommLinks connection parameter of your application's connection string.

Set the UseUDP parameter to off to prevent UDP packets from being used to locate the server. You can use the short form UDP.
Set the ClientPort parameter to a range of allowed values for the client application to use. You can then configure your firewall to allow these packets across. You can use the short form CPort.
Set the HOST parameter to the host name on which the database server is running. You can use the short form IP.
If your database server is not using the default port of 2638, you must specify the port it is using, in the ServerPort parameter. You can use the short form Port.

In this example, the connection string fragment:

Restricts the client application to ports 5050 through 5060
Disables UDP packets
Connects to a server named myiq running on the machine at address myhost using the server port 2020:

CommLinks=tcpip(UseUDP=OFF;ClientPort=5050-5060;Host=myhost;Port=2020;Eng=myiq)

Additional Information

Administration: Database > Connection and Communication Parameters.