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HP Recommended

Hi folks,

 

I've just spent the last two days chasing a problem with an HDX deployment.  Now that I've found the solution, I'd love if someone better informed could explain it to me so I can avoid this ever happening again.

 

The endpoint in question is an HDX 7000 intended primarily for point-to-point H.323 use.  The system is installed on a small LAN managed by a Cisco SRP521W with a 10Mbps symmetrical PPPoE connection to the Internet.

 

Upon installation the HDX was assigned a fixed IP address and hosted in the SRP's software DMZ.  Calls were successfully made to a variety of sites without issue and the deployment was considered a success.

 

This week my client contacted me complaining they were unable to connect to a VMR assigned to them by a large educational institution.  I double-checked all of the network settings within the HDX and the SRP.  I made multiple successful test calls point-to-point from my desktop client, to both of Gary Miyakawa's VTC Callback endpoints, and an RMX 2000 MCU at a university running firmware v7.8.0.  Everything checked out.

However calls made to the problematic VMR would consistently establish all but the Video Rx stream, which would always remain at 0k Video Rate Used and 0fps Frame Rate.  Classic firewall stuff, right?  This was consistent for any/all VMRs on that MCU, which as it turns out is an RMX 4000 running firmware v7.6.1.

 

The solution ended up being changing the NAT Configuration setting on the HDX from Off to the system's public IP address.  That was all.

 

What I want to understand is why?  I understand the issues that NAT can cause with H.323, but I don't understand why this problem only reared its head with that particular RMX 4000 and not with the RMX 2000, HDX 8000 and RealPresence Desktop systems I was already able to call without issue.

Interestingly, I found during my probing that if I disabled the NetMeeting Application Layer Gateway on the SRP I was no longer able to place calls to the HDX from the outside - which I really wouldn't have thought should be an issue given the HDX is hosted in a DMZ.

I'd love to hear the community's thoughts on this one. Cheers.

2 REPLIES 2
HP Recommended

Have you searched the Board for 'NAT' - there are many responses that describe how the HDX uses NAT. Also described is the HDX check box 'NAT is H323 Compatible'.

HP Recommended

Hi Kendo,

 

Yes, I have searched the Board extensively as part of my fault-finding and devoured all the literature I could find.

 

From what I have read in your previous responses to other users, I understand that by enabling NAT Configuration -without- NAT is H.323 Compatible checked, I am forcing the HDX to report its WAN IP address in layer 7 of the packets.

 

Great! That was obviously the solution.  What I need to understand now is why?

 

I gather that network address translation still needs to take place between the WAN and LAN, irrespective of the fact that the HDX is hosted in a DMZ and no port filtering is being performed?

 

Okay.  Well how, then, could the performance be so idiosyncratic?  If that setting was the problem all along, shouldn't it have crippled all H.323 calls?  I could understand if all point-to-point calls worked perfectly but the system fell over only when making calls to bridges (plural), but the fact I could dial one RMX flawlessly and have persistent trouble with another does my head in.

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