ICE, multiple interfaces, RTP timeouts

[Mike Remski]

Looking for a few ideas of where to start looking.
Node.js application, not running in a browser, using node-webrtc to
provide the webrtc bits.
Call setup completes, but getting an RTP Timeout error after getting to
call confirmed state.
The host running the application has normal ethernet connection and
also a VPN up at the same time. VPN is also going out the normal
ethernet connection.

Packet captures on the host running the application show that ICE
gathering completes, there are legitimate ICE candidates on the
ethernet interface, not for the VPN. I'm not expecting any candidates
for the VPN connection.

The RTP Timeout is happening because of the VPN interface not having
any ICE mappings. I'm not sure if the ICE gathering should have
stopped because it has good candidates and simply discarded the VPN
interface or if there is something else needed.

What I'm looking for:
Is there a configuration option that would affect what interfaces to
actually use for RTCPeerConnections?
Is there a way/configuration/event that I can force the use of the
discovered candidates?

Thanks for any hints.