To change an OS/400 IP address, TCP/IP must be turned off, which means the majority of work must be done on a green screen, rather than through a TCP/IP-connected iSeries Operations Navigator. Taking down TCP/IP will result in a system outage, so you'll have to perform your address changes within a suitable maintenance window (usually on weekends or a holiday). You can disable TCP/IP and the Client Access host servers by executing the End Host Server (ENDHOSTSVR) and End TCP/IP (ENDTCP) commands, as follows:

ENDHOSTSVR SERVER(*ALL)
ENDTCP

Make sure that all users are off the system before taking down TCP/IP, and that all production subsystems that rely on TCP/IP connectivity are also down. If you want to put your iSeries or AS/400 into a restricted state as you change addresses, you can perform an End Subsystem (ENDSBS) command with the *ALL option, as follows:

ENDSBS *ALL

Remember that an IP address change may also involve a physical act, such as moving the machine or running a new network cable that attaches your box to a different router or hub. Coordinate with your LAN/WAN people to make sure that all physical moves are in place before you make your TCP/IP changes.

Most of the work in changing your OS/400 IP addresses happens in the Configure TCP/IP menu (accessed by typing CFGTCP from the command line). It's been my experience that it's best to change the following items, in the following order, to replace an existing IP interface (note that option numbers are listed for OS/400 V4R5 and V5R1 machines; older OS/400 versions may use different option numbers for the same functions):

1. Delete any OS/400 host table entries that point to the IP address to be changed (CFGTCP, option 10, Work with TCP/IP host table entries). Record any entries you deleted for later restoration with the new addresses.
2. Delete any TCP/IP routing entries that will be replaced (CFGTCP, option 2, Work with TCP/IP Routes), documenting the options contained on each entry you delete. For many AS/400s, there is only one routing entry that is designated for the default routing destination (*DFTROUTE). In some circumstances, you may find that you cannot delete your old TCP/IP interfaces without first removing the *DFTROUTE entry, even if the routing address isn't changing. So be aware that you may have to delete the *DFTROUTE entry, and be sure to document that entry before you remove it.
3. Delete any TCP/IP interfaces that will be replaced, using option 1 off the CFGTCP menu, Work with TCP/IP interfaces, and placing a 4=Remove in front of the addresses you want to delete. In particular, note the OS/400 line description the deleted IP addresses were attached to.
4. Add each of the new IP addresses to the system as new interfaces attached to your communications line, complete with the proper subnet mask and line description. New IP addresses are added through option 1 off the CFGTCP menu.
5. Add back any routing entries you deleted in Step 2. Use option 2 on the CFGTCP menu to create duplicates of the deleted entries, with one exception: The restored entries should have the new hop routing address (which you defined in your homework phase), if that address is changing.
6. Add back the deleted host table entries from Step 1 by using CFGTCP, option 10, but use the new IP addresses that replaced your old addresses.
7. If your AS/400 needs to use a new DNS server list because it moved to a different network segment, change the system's DNS IP address list by using CFGTCP, option 12, Change TCP/IP domain information.
8. If your AS/400 has any relational database entries that reference the old TCP/IP addresses, change them by using the WRKRDBDIRE command to update any entry that must use the new IP address.
9. Bring your AS/400 out of restricted and make sure that the new addresses work.

This is the easy part. However, because your machine doesn't live in a biodome, you'll also need to inventory your network before you make the change, to find any other computers that access your iSeries or AS/400 through the old IP address. To that end, you also have to cover the following items:

• Work with your LAN/WAN administrator to coordinate DNS entry changes, so that both your internal and external networks point to the new IP addresses for your AS/400 host name. The timing is tricky here, because these changes need to happen at approximately the same time as your AS/400 IP address change, and DNS changes may take several hours--or even a day or more--to ripple through your network and the Internet. This is another good reason why you might want to change your IP addresses during a low-activity maintenance window (such as Sunday morning or a holiday).
• Check your other OS/400 boxes (if present) to see if they are pointing to an expiring IP address, either through the OS/400 host table (CFGTCP, option 10) or through their relational database entries (WRKRDBDIRE). Change these entries as needed.
• Identify any machines (AS/400 or otherwise) that may be printing to OS/400 output queues using LPR/LPD printing. For OS/400 printer queues, display the output queue description (accessed by typing in the Work with Output Queue command, WRKOUTQ, and taking option 8=Description for your target queue) to see if the queue is pointing toward one of your deleted IP addresses. If the queue is pointing to an obsolete IP address, stop the OS/400 remote writer by issuing an End Writer (ENDWTR) command for that printer, and then change the IP address on the printer output queue by using the Change Output Queue (CHGOUTQ) command. After changing, restart the writer by using the Start Remote Writer (STRRMTWTR) command.
• Identify any network desktop machines that may be using the old IP address in a host table or hard-coded into a program for use with IBM's Client Access or another client-based program. In a perfect world, all desktop machines would be accessing your AS/400 through DNS entries--which would allow you to make the change for many machines in just one location--but you might be surprised at how many desktops are using a private host table that needs to be changed. Identify and change any other programs on any other servers that are hard-coded with your obsolete IP address. Change as necessary.

The hard part about an OS/400 IP address change is identifying all the areas that reference the old address and changing those items accordingly. However, if you use this list as a starting point and do your homework in advance, it can make the job easier.

Sponsored By TRAMENCO

Introducing a New Source for Training and Mentoring. Follow this link to a vital new source for how-to technical information: www.tramenco.com. Unlike companies that offer training as an afterthought, The Training and Mentoring Company (Tramenco) is dedicated to just one thing: Advancing your career by giving you the skills you need to solve real-world business problems. You get the best information from the world's leading experts--Howard Arner, Kelly Conklin, Don Denoncourt, Susan Gantner, Skip Marchesani, Glen Marchesani, Shannon O'Donnell, Craig Pelke, and Richard Shaler. Choose from a menu of training options to fit your needs: onsite seminars, public seminars, mentoring, consulting, books, CBTs, and Web-based training. And make plans to attend the 2002 iSeries Connection Conference, the multi-day, multi-track conference that was the only sold-out iSeries training event this year, co-sponsored by the Education Connection and Tramenco. For more information about Tramenco's career enhancing opportunities, call (800) 421-8031 or go to www.tramenco.com.