Re: Dynamic server ports

[thomas@xxxxxxxxxxx]

Walden:

On Thu, 13 December 2001, "Walden H. Leverich" wrote:

> As I understand it CA Express has a dynamic port mapping scheme. There is
> one port (8477?) that is static and the job of that port is to hand out the
> ports for the other connections. So when telnet wants to connect it connects
> to 8477 and says "What's the telnet port?" The answer is (usually) 23 and
> then telnet connects to port 23.

I suspect you're referring to the server mapper (as-svrmap tcp) service that 
normally runs on port 449; port 8477 would normally have the as-netdrive 
service.

Essentially, you connect to port 449 and send in a name from the service table 
such as "telnet" or "ddm" (case-sensitive and ASCII) and it returns a 32-bit 
binary port number for that service. To see it in action, just set up a comm 
trace and watch any PC connect. I have no idea how the same is handled on other 
platforms; it'd sure make a nice standard.

> Is there a way to add new things into that process? I have pc processes that
> need to connect to the AS/400, can I use this port-mapping routine for my
> own use too? I'd rather be flexible rather than hard-code the ports.

You can add entries to the system service table by using the Add Service Table 
Entry (ADDSRVTBLE) command. Really pretty simple once you've done it a couple 
times and works well. I use it to register my own sockets applications for 
AS/400 networks -- just have to remember to use QDCXLATE or some other means to 
make sure I'm talking ASCII. You might also consider using the Add TCP/IP Port 
Restriction (ADDTCPPORT) command to keep your chosen ports from being used by 
OS/400 for other purposes, and, of course, choose port numbers that will play 
nice with others.

Tom Liotta

--
Tom Liotta
The PowerTech Group, Inc.
19426 68th Avenue South
Kent, WA 98032
Phone  253-872-7788
Fax  253-872-7904
http://www.400Security.com


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