SPA3102 - Doesn't forward calls to IP on LAN without WAN connection

[leo.spalteholz]

I apologize for misuse of terms, we're new to the VOIP world.

We have the following setup:

Outside line to SPA3102 Line jack.

Handset on SPA3102 phone jack.

Linux computer running Asterisk on Ethernet port, static IP.

The system is a custom frontend to a home monitoring system that allows people to call in to get information about the system.

Everything works fine if the SPA3102 is connected to the WAN.  The call is passed to Asterisk and is handled correctly.  

As soon as the WAN connection is unplugged (a requirement for our system), everything stops working.   Calling in to the line results in no answer (endless ringing for the caller, but the handset never rings). The call appears not to be ever passed to Asterisk.

We're a bit in the dark about where to start looking.  Is there anything on the SPA3102 side that would depend on an internet connection for this use-case?   We are just passing incoming calls to a static IP on the LAN.   Of course it could be on the Asterisk side, but logs indicate that Asterisk never receives the call when the SPA doesn't have internet, so we are leaning towards a problem on the router side.

Thanks for any clues.

[leo.spalteholz]

More information:

Everything works if there is any ethernet connection on the WAN port, it does not have to actually be an Internet connection.

For example, if I set the WAN IP to static (192.168.1.1) and then plug in a computer the whole system works again even though the SPA doesn't have access to the internet.   It seems that as long as that Internet LED on the front of the router is lit up, the system works fine.

[leo.spalteholz]

Found a workaround:   If you put the Asterisk box on the WAN port and set the IPs appropriately, it works.   

Not ideal, as this will make debugging more of a hassle in the field, but at least it works.  

Still would love to know why the SPA seems to completely break if it doesn't have an ethernet connection in the WAN port.