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This blogs explains the communication between Dispatcher of an ABAP application server instance to the Message server of the central ASCS instance. Many customers want to use additional hostnames on Windows to separate SAP TCP/IP communication from other traffic. This blog shows  how to configure this.

The following picture shows the communication of an ABAP instance to the Message server, if no additional IP addresses are bound to Windows:


Let's assume, the hostname "alpha" and its IP address should not be used. We create another hostname in DNS "beta", bound the related IP address and configure Windows according to SAP note 1564275 - Install SAP Systems Using Virtual Host Names on Windows.

The ABAP application server instance is installed using the additional hostname "beta". In the instance profile you find "SAPLOCALHOST = beta" and if you open SAP MMC, the hostname display for this instance is "beta".

But which IP address is used to communicate with the message server?


The answer can be seen in dev_ms (Message server trace file) of the ASCS instance work folder:

[Thr 6056] LOGIN: beta_SID_00 [10.10.0.13] (DIA UPD BTC SPO UP2 ICM )

The dispatcher still uses the IP address of hostname alpha for communication with the message server.

Reason:

SAP applications use the FIRST IP-address for outbound communication which will be returned by the operating system.

Solution:

Add this profile parameter with the IP address or hostname you wish to use for outbound communication, to the ABAP instance profile:

is/local_addr=beta

Restart ABAP instance and check dev_ms afterwards, it the correct IP address is used:

[Thr 6056] LOGIN: beta_SID_00 [10.10.0.99] (DIA UPD BTC SPO UP2 ICM )