Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Fri, 08 Dec 2000 19:05:49 -0600

Mathew Rippa wrote:
> 
> Has anybody experienced problems with the LanGpib driver from Benjamin Franksen
> (any version) returning the wrong ioc address? I have consulted Peter Mueller
> (from Bessy) on this. It looks like a bug in the call to
> "get_myaddress(&iocAddr)".
> 
> The driver returns only 128.171.0.0 when our actual address is 128.171.90.150
> .. As a result it incorrectly thinks our gateway is 128.171.0.59,  which is
> actually 128.171.90.59 .  Verbose details below...

In section 2.4 of the lanGpib documentation, ie at
http://www-csr.bessy.de/control/SoftDist/gpib/doc/lanGpib-8.html#HEADING8-0
there is a paragraph labeled WARNING indicating that the driver does not
use the IOC's _subnet_ mask but its _netmask_ to determine the box's IP
address.  128.x.x.x is a Class B address, so your netmask is 255.255.0.0,
although your local subnet mask may be 255.255.255.0 (which is irrelevent
for this driver).  The link part of your GPIB hardware addresses need to
have 90*256=23040 added to them.  This caught us at APS the first time
too.

There is a quick reference for IP address classes at
http://foldoc.doc.ic.ac.uk/foldoc/foldoc.cgi?Internet+address

Ben - I suggest you revise the wording of that paragraph, and maybe add an
example as well to make it more obvious.  Something like:

WARNING: The IP address of the gateway is determined by combining the
value in the link field with the network part of the IOC's address, not
the subnet part.  If the gateway's IP address is A.B.C.D and A is between
128 and 191, then you have a class B network, so your link address must be
C*256+D.  If A is between 192 and 223 then you have a class C network, and
the link address is just D.  If A is less than 128 and B is non-zero, you
can't use this driver.

- Andrew
-- 
Every great idea appears crazy to start with.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System