Can ping but not connect to real time system

[cirrusio]

Hello all,

I have a funny little issue that has arisen recently.  I have a PXI chassis running a RTOS that I am able to reach using LV and MAX when I am sitting on the LAN.  I have the chassis in a DMZ, so it is directly exposed via the network external IP.  Recently, I had to reformat the drive and now for some reason I can not access the system via MAX or LV externally (I could before).  I can ping the instrument, but it does not seem to respond via MAX or LV.  There are no errors on the target and the target is not currently running a start up VI.  Does anyone have any thoughts?

Thanks, m

[Sam_Sharp]

When you say reformat the drive...did you reinstall the RTOS and/or reinstall the LabVIEW Software Set for the device? To me, reformatting the drive results in wiping everything off the drive. You'd need to reinstall the RTOS and then reinstall the LV software set.

There are some instructions here - they might be different depending on the chassis / MAX versions you have installed...

http://digital.ni.com/public.nsf/allkb/6B1343F61905203386257051006573CA?OpenDocument

http://digital.ni.com/public.nsf/allkb/A47CB1C917D1D1EC8625781B00722F99

Have you tried booting the chassis into safe mode - does it show up in MAX then?

[cirrusio]

Sigh... OK, so this apparently was not clear from the original message....I can access the system using LV and MAX from the LAN (have no problem running my code on the target while on the LAN), but am unable to connect using these two environments when not on the LAN (i.e. outside of my office).  I should also state that the IP has NOT changed (same IP on the LAN that I was accessing the system with before), so this is very unlikely to be an issue involving a conflict with another device with the same IP.

[Bob_Schor]

Matt,

     I'm having trouble understanding what you can and cannot do.  As I understand it, "from your office" (whatever that means), you can "see" the device in MAX, you can run "code on the target while on the LAN" (not sure what this means, but I assume it means that you open LabVIEW on your PC, open the Project, and hit the Remote Run button).

     I know you said that the Target is in a DMZ.  Does that mean that what does not work is trying to run the program from an outside IP, through the DMZ?  That does sound a little tricky ...

Bob Schor

[cirrusio]

Hello Bob,

LAN === local area network - you are generally on some kind of local area network when operating in most environments.  This is simply where traffic is routed through a single IP (provided usually by an ISP).

DMZ - this has multiple definitions but in this case, I have allowed direct access to an IP (the one of the PXI system) through my ISP IP.  This means that if you ping the IP provided by the ISP you will get a response from that chassis.  The reason that I put the chassis on a DMZ rather than just opening up some ports is that I was never able to do this successfully despite the outline of the ports used provided by NI.

In the past, I had no problem doing this with the same chassis using the same IP.  And, right now, if I provided you with the IP, you could also get the system to respond to a ping.  Unfortunately, the system will not respond to a connection request from MAX or LV when I am not on the same subnet.

m

[Sam_Sharp]

Ah ok - I thought your problem was that after formatting you couldn't access the chassis via MAX/LV.

One thing I can think of is that MAX uses UDP for some of the functionality in communicating with targets (e.g. I think it uses UDP for discovery, but TCP/IP for commands) - UDP packets don't always travel well through different subnets - particularly if they are broadcast packets (which are used for discovery). I think that's why there's an option to add a target by IP address.

The other thing I can think of is that your PXI chassis is configured to have a LAN address (typically 192.168 or 10.X), but because of the DMZ it's actually accessible via a WAN address - it might be refusing the connection (IP settings mis-match?) and/or something is happening with the handshaking between the chassis and MAX/LV.

The final thing could be that your PC/IT firewall might be blocking incoming connections - most firewalls allow outgoing connections (e.g. to a web server) but block incoming connections (e.g. if you were the web server). Of course, as your chassis is in the DMZ, there aren't any firewalls on the chassis side, but maybe it's trying to make an incoming connection.

[cirrusio]

It is on a DMZ, so there is no firewall.  And, let me be clear - I had no problem accessing this chassis prior to the reformat.

What do you think the IP settings mismatch might be?

[cirrusio]

 So, using nmap I just did a scan of ports 1-20k.  Only one that seems to be responding is 4567.  I think this might be a router port so it seems that there are no ports associated with this chassis open.  I will have to take a look at my network settings later and see what the issue might be...

[cirrusio · Accepted solution]

nm - I don't know what was going on, but all seems well now...I had the wrong IP today.

For those who are interested, this is what an nmap report on the IP will look like if you do a scan from 1-10k on a PXI chassis located on a DMZ (I am not forwarding any other ports, but some ports such as 80 are responding on machines located on the network):

Thanks for all of your attention.  m

[cirrusio]

And accepting my own post which actually has no solutino seems a bit gratuitous, but I just wanted to make sure that this didn't appear as an open issue.  Sorry. m