Based on recent empirical findings, and based on various posts on the web, it seems that an application running on an iPhone with personal hotspot enabled cannot send broadcasts and/or multicasts out onto the personal hotspot's network. Can anyone shed light on the cause of this problem?
I have an IOS application, built with cross-platform C++ code, that broadcasts and multicasts its presence onto the network it is running on. The application works flawlessly when the iPhone is connected to a Wi-Fi network. In this case, other devices on the network receive the broadcasts/multicasts, and everything functions correctly. This can be verified easily by connecting a computer running WireShark to the network -- the broadcast/multicast packets can be seen in the packet trace.
Needless to say, the application works well on an iPhone connected to a local Wi-Fi.
When I run the application on an iPhone that has its personal hotspot enabled, no broadcasts/multicasts are released onto the hotspot network. This can be verified using WireShark, which shows no such packets in its trace.
Is there any constraint regarding using a personal hotspot as a network router capable of handling broadcasts and multicasts?
When I requested a web page on my "WireSharking" device using a browser, the personal hotspot responds correctly to all packets, returning the web contents.
I have come across other Stack Overflow pasts that report the same, or similar, problems:
- TCP connection not working properly when using iPhone as hotspot
- Fail to send ssdp broadcast by personal hotspot
A good tutorial for writing such a broadcasting/multicasting application on iPhone is Michael Tyson's "The Making of Talkie: Multi-interface broadcasting and multicast". Suffice it to say that my application conforms with all requirements (e.g., setting socket options SO_BROADCAST, SO_DONTROUTE, and IP_MULTICAST_IF where appropriate).
A reply to reference (1) above writes "Could it be because the personal hotspot introduces Network Address Translation?". I filtered the WireShark traces to show only packets connected to the hotspot IP, and there is no evidence of the personal hotspot sending anything to a NAT address.
Can anyone explain why an iPhone running a personal hotspot does not broadcast/multicast packets, and how to solve the problem?
Many thanks in advance.
P.S. I originally posted this query on Stack Overflow, and learned about this more Apple-oriented forum.