I had some vague idea that on z/OS, the Resolver can use some or all of:

1.     DNS

2.     Its own configuration data sets, via GLOBALIPNODES statements

3.     /etc/hosts

I just spent some time looking at IBM doc, and what I found seems to support 
this. What I couldn't seem to grok was whether you can control the *order* in 
which the three are used: that is, can you say "OK, we use the DNS server at 
this IP, but we want to look in /etc/hosts *first*"? There's lots of discussion 
of the "search order", but nothing that clearly indicated (to me, at least) 
that you could control the *order*. It does look to me like you could specify 
/etc/hosts on a GLOBALIPNODES statement, but that isn't quite what I mean.

What I'm really looking for is a way for a user-possibly a sysprog-to define or 
override a hostname-to-IP mapping to test something. We keep coming across 
customer systems that don't have a DNS entry for a server that uses SSL (TLS), 
and getting a DNS update requires an act of Congress, so we wind up waiting. 
Some of them know they can't update /etc/hosts, but if they can, it doesn't 
always seem to take effect.

I see lots of ways (for example, in this marathon post by Chris Mason: 
 that a name can get resolved. And I found COMMONSEARCH/NOCOMMONSEARCH, which 
at least explain differences between POSIX-land and batch jobs, but Chris's 
list of 13 paths mostly just raises more questions.

And I realize that the answer may be "it depends", based on which of the 13 are 
configured currently. Ideally, there would be a foolproof way for a user to 
mess themselves up when they wanted to. Is this a pipe dream? I can imagine 
that it might not make sense-it certainly doesn't most of the time!-but it sure 
would be a handy technique if 'twere available.

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