Setting up a backup proxy server for SPA50x

Unanswered Question
Aug 27th, 2010


I would like to set a backup proxy server (SIP) on my SPA508G. I've looked at the documentation, and it does mentions the phone support backup proxy server with the DNS SRV method, but that's not what I want.

In fact, I've not completely understood the behavior of the phone if a backup proxy server is configured and the primary proxy server becomes unavailable. For exemple, if I make a call in this situation, will the phone automatically try to send its SIP INIVITE to the backup proxy server ?

In the Ext1 tab, in the 'Proxy' field, I've tried the value '' but it didn't worked (well, the phone didn't tried to fallback on after I've made unreachable).

Any ideas ?


I have this problem too.
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blablablab Wed, 09/01/2010 - 08:40

Thanks, my first understanding on how this was implemented on the Cisco SMB was wrong, that explain why I had trouble setting it up.

There's a small problem though. So let's say I have a main and secondary proxy. If I cut the connection between the phone and the main proxy, and then call an extension with my phone, it sometimes takes too much time for the phone to try the secondary proxy and the turn this into a 'no response'. This doesn't seem to happen frequently, and only after the phone has rebooted. Are you aware of any similar issue ?

I've done the tests on a SPA504G with firmware version 7.4.4.

cdh Mon, 02/21/2011 - 15:41


I have tried to setup the manual SRV on the SPA504 according to your document and it will not register if I use the SRV= format no matter what I try to do with it.  It will only register if I use a single IP address or DNS name.  I cannot access DNS to make the changes, so I need the manual SRV format.  I am using 7.4.3a on the SPA504G.  What am I missing?


Alberto Montilla Tue, 02/22/2011 - 05:37

Dear Chris;

Please upgrade to a later firmware, to ensure this is not a bug/defect on an early firmware version. After doing that, if problem persists, please send your phone html configuration (full page .mht) to check config is ok.


cdh Sun, 02/27/2011 - 19:56

The very first thing I did, before posting, was to upgrade the firmware.  The did not help.

I am posting the mht file as you requested.  This is becoming urgent, as the system had to go live without any redundancy,

so I need to resolve this without using DNS SRV records.

Thanks for your help,


Alberto Montilla Tue, 03/01/2011 - 10:01

Dear Chris;

I may need to check with the expert as I have conflicting info, but before that I think it is easier that you perform the test. Please stay tuned.


Patrick Born Thu, 03/03/2011 - 11:16

Hi Chris,

Alberto asked me to assist with this. I will get to this early next week and will provide you with an update then.




One reference document to locate SPA phone resources

Patrick Born Tue, 03/08/2011 - 16:49

Hi Chris,

I ran through your config in my lab and it all works as expected. I wrote this document and included some trace information that may offer you some clues:

Run a Wireshark trace to see what the phone is sending out. Notice on page 3 of the link that I provided, packet 24 the phone registers to the primary proxy and sends INVITES to [email protected]_proxies in my example.

Once the primary proxy has failed, the phone does not attempt to register to the secondary proxy, it sends an INVITE to the secondary proxy, shown in packet 118, at which time the target phone starts ringing.




Patrick Born Tue, 03/08/2011 - 16:37

Hi Yvan,

When the primary proxy fails the phone will automatically switch over to the secondary proxy and the call will be routed. The user making the call will experience a short delay, in the order of seconds during the time that the phone takes to realize that the primary proxy is not responding.

This document may help:




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