Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!CITHEX.CALTECH.EDU!carl
From: carl@CITHEX.CALTECH.EDU (Carl J Lydick)
Newsgroups: comp.os.vms
Subject: Re: Testing for a node
Message-ID: <880421103649.1827@CitHex.Caltech.Edu>
Date: 21 Apr 88 17:47:30 GMT
References: <264@csvax.liv.ac.uk>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 22


 > Testing for a node the noddy way:
 > 
 >   Attempt to assign a channel to NODE::NL:
 > 
 >   As NL: is a shareable mailbox template device, the only way the assignment
 >   will fail is if NODE doesn't exist or is offline in some way.

Well, you're getting closer, but still no cigar.  If the  node  is  reachable,
but  remote file access has been disabled, this method will incorrectly report
that the node is not reachable, unless you check the error messages correctly.
I  guess  that's  the  bottom line:  to find out if the node is reachable, try
performing ANY DECnet operation that doesn't have unwanted side  effects  (for
example,  you probably don't want to create an umpteen-megabyte file).  If the
operation succeeds, the remote node is reachable.  If it  fails,  examine  the
status  and/or  error messsages.  If they don't say the node is not reachable,
then the node IS reachable, but you tried doing something it didn't allow.

By the way, NL:  is NOT a template device.  The  only  way,  for  example,  to
create  NLA1:   is  with SYSGEN or something functionlly equivalent.  Also, if
you try to create a null device that's out of range (NLA8:, as  I  recall,  is
the  first  such),  you'll crash your system (that's why I don't check to make
sure that NLA8:  is the first illegal null device).