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Craig Pelkie Bits & Bytes Programming, Inc. craig@web400.com

Working with the AS/400 Service Table Edition SERVICETABLE_20020221

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Bits & Bytes Programming, Inc. Valley Center, CA 92082 craig@web400.com

Copyright © 2002, Craig Pelkie. All Rights Reserved

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Working with the AS/400 Service Table

Copyright © 2002, Craig Pelkie, ALL RIGHTS RESERVED

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Working with the AS/400 Service Table When you use a TCP/IP function on the AS/400 system, your request is processed using a combination of the IP address and a port number. For example, the default port for TELNET is 23. The list of port assignments is kept in what is called the service table. On the AS/400 system, you can view the service table by using the Work with Service Table Entries (WRKSRVTBLE) command. The command displays or prints a list of services, port assignments and protocols associated with a port (see Figure 1).

SRVTABLE01

Figure 1: The Work with Service Table Entries command displays the list of services, ports and protocols.

Services that are specific to the AS/400 system use the prefix “as-“ as part of the service name. For example, you can see in Figure 1 the services for the HTTP Server administration program and several of the services for Client Access Host Servers. Each service can be assigned up to four aliases (see Figure 2).

Working with the AS/400 Service Table

Copyright © 2002, Craig Pelkie, ALL RIGHTS RESERVED

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SRVTABLE02

Figure 2: Each service can be assigned up to four aliases.

How the Service Table is Used When Client Access needs to use a Client Access Host Server, it sends a request to the server mapper on port 449 to locate the required host server. The server mapper looks in the service table for the name of the required host server. It then returns the port number for the host server to the requester.

Port Assignments Port numbers are assigned within the range 0—65535. The first 1024 ports (0—1023) are called assigned ports. By convention, those ports are used for specific functions. The usage of ports within that range is documented and by convention, no other function may use a port within the range. Software providers who need to use a port within that range must apply to the Internet Assigned Numbers Authority (IANA) to get a port assignment.

The range of ports from 1024—65535 is generally open for software providers to use. Within that range there are many registered ports, which are ports that software providers have advised IANA that they are using. There is no requirement that other software providers avoid using a registered port for another function.

Because the ports in the upper range may be freely used, you need to be aware of what ports are used when you install TCP/IP applications and servers on your AS/400 system. For example, the Client Access Host Servers use the range of ports 8470—8479. Although it is unlikely that another application on your AS/400 system will use those ports, there is nothing that prevents the ports from being used.

Working with the AS/400 Service Table

Copyright © 2002, Craig Pelkie, ALL RIGHTS RESERVED

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Remapping a Port Assignment If you install a conflicting application, you can remap port assignments on the AS/400 system using the WRKSRVTBLE command. The steps to remap a port assignment are:

1. Use option 5 to display the current port assignment (Figure 2). You should print the service table entry, since you will need to enter all of the information about the service in a new port assignment.

2. Use option 4 to remove the current port assignment.

3. Use option 1 to add the new port assignment. Enter all of the values that were used for the originally assigned port (particularly the aliases).

Additional Information You can view the authoritative list of assigned and registered ports in the Request For Comments (RFC) document RFC1700. You can locate the document at the following URL:

http://www.ietf.org/rfc/rfc1700.txt

The list of assigned and registered ports starts on page 15 of the RFC1700 document.

Working with the AS/400 Service Table

Copyright © 2002, Craig Pelkie, ALL RIGHTS RESERVED

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