Luckily, the same architecture document says:
AIR VIDEO UPNP MAPPING NOT POSSIBLE PC
Obviously, by default our PC behind the Router 2 can't get multicast advertisements from Router 1 and the Router 1 can't get multicast search messages from PC, so we have a problem here and the question now is whether there is a possibility for communication without multicast. There are two main mechanisms for discovery - advertising (when the device periodically multicasts some information about it) and search (when the control point sends multicast search message and the device answers to that with unicast response). But to get to the description step we need to have a URL of Router 1, so let's take a closer look at how this URL is acquired the normal way. So, what all of that means for double NAT is that in description and control steps of UPnP interaction we have zero problems communicating from PC to Router 1 as all of that is just standard TCP with unicast IP addresses. SSDP uses UDP for its transport with port number 1900 (by default) and well-known multicast address.ĭescription starts with URL provided by the device at discovery phase, the control point (that is PC in our case) needs to issue an HTTP GET request on this URL and that means it uses TCP as a transport protocol with devices IP address (unicast).Ĭontrol starts with URL provided by the device in its description, and it uses SOAP on top of HTTP on top of TCP which in turn also means unicast IP for us. So the main things to be concerned about are discovery, description and control.ĭiscovery works via SSDP message exchange. Eventing and presentation are also almost useless in our case. There are several distinct steps of UPnP communication as per UPnP Device Architecture version 2.0:Īddressing is of little interest for us, let's assume proper DHCP everywhere and be done with it. So let's try to approach this issue from a pure theoretical point of view with two plain UPnP routers/NAT devices.
There is an IGD-PCP IWF specification that tries to solve similar problem, although it assumes PCP support on your "Router 1", not UPnP.
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