CX500 – Network error

As all blogs should, I’ll start this one with a personal experience…

Just recently (sound familiar yet?)..

I had configured the CX500 as per usual as a common area phone. It signed in beautifully once I added the telephone number (without the + of course) and the accompanying PIN.

When I rebooted the phone it showed the boot cycle and then got stuck on a screen saying that there was no network detected. It then presented me with the configure device options as if it had forgotten the telephone number and PIN. Once I re-entered these it logged in as before.

Right so if I have a power outage my device isn’t going to automatically login with the cached credentials…not good.

For giggles I first updated the firmware on the CX500, same behaviour. Checking the device I noticed that the DHCP request was going unanswered and the CX500 wasn’t getting an IP..DHCP problem?? NO!

After much packet capturing and head scratching the culprit was discovered. The switch of course, a Spanning Tree Setting was delaying the DHCP request from reaching the DHCP Server. That should cause the error we are getting you may say…

The CX500 sends only 4 DHCP requests (in rather quick succession), normally 1 will suffice and get a response. In my case the delay injected by the switch prevented a timely answer. The CX500 then goes into “I give UP” mode, and then sits there waiting on the “credentials” page. Once the Credentials are re-entered further DHCP requests are sent.

Changing the switch port solved the issue.



About Paul B

My name is Paul Bloem and I am employed at Lexel Systems in New Zealand as a Principal Consultant for Unified Communications. I have been working on enterprise voice solutions for over 20 years. My first 10 years were spent working for a Telco in South Africa (Telcom SA). This is where all the groundwork happened as I was exposed to just about every aspect of telecommunication you could imagine. I develop an interest in PBX technologies and eventually became the go-to guy. Next, I had a 10 year run at Siemens South Africa, most of my time there was as a Technical Trainer. During this time VoIP hit the world stage, I had the privilege of introducing VoIP both as H.323 and later SIP across the Siemens HiPath 4000 solution stack. In 2008 I immigrated to New Zealand with my newly attained MCSE, I was ready to go where no PBX Techie had gone before. I was employed to explore OCS 2007 and that was pretty much the beginning of the end for me. I have been working on OCS and Lync ever since. My current role focuses exclusively on Lync and associated technologies.. That includes pre-sales, consulting, architecture and design, training and support. I even get to play in the development space from time to time - focus on play ;-) I was nominated as a Microsoft VTSP for Lync early in 2013 and also awarded Microsoft's MVP award for Lync in 2014.
This entry was posted in CX500, CX500 - Network error, Devices, DHCP, Polycom. Bookmark the permalink.

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