Is the VTAMAPPL Service statement required for FTP and what is the effect of changing or removing it?

Document ID : KB000048659
Last Modified Date : 14/02/2018
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The VTAMAPPL SERVICE statement must remain unchanged in order for FTP and FTP2 to function.

This comment in the APPCFGxx parameter member is included with the install:

* VTAMAPPL needs to be on port(23) for client ftp/ftp2 to work properly

This has been of concern to some customers required to remove port 23 as a Telnet port.

When you look at SERVICE statements, the only ones that denote a Telnet
listener are those with


 SERVICE NAME(xxxxx) MODULE(STELNET) ....     
 SERVICE NAME(xxxxx) MODULE(T01S3270) .... 
 SERVICE NAME(xxxxx) MODULE(T04STSSL) .... 

Any other MODULE is not creating a Telnet listener.

As you can see, the VTAMAPPL statement is not using a Telnet module:

SERVICE NAME(VTAMAPPL) MODULE(VTAMAPPL) PORT(23) NOCPASSWORD

The VTAMAPPL statement is required as FTP creates an internal Telnet session on port 23, so the port must be available to the stack itself or FTPs will fail.

Issuing the command NETSTAT CONN REMPORT(0) will show all listening ports.
If you are only using port 23 for the VTAMAPPL and not Telnet, you will not see a listener on that port.

So please do not remove or change this statement.
No one can gain access to the stack through the VTAMAPPL statement but it is correct that FTP requires its presence.