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> Did a bunch of apps specifically abuse multicast networking? My first thought was: how does multicast IP traffic interact on cell networks? IPv6 makes heavy

> Did a bunch of apps specifically abuse multicast networking? My first thought was: how does multicast IP traffic interact on cell networks? IPv6 makes heavy use of multicast (e.g., NDP), and a lot of mobile network are now IPv6-only (clients do no get IPv4 addresses), and so if apps can start sending tracking to "everyone" on the network (or a particular base station), could that cause problems.

neilalexander 5y ago
Cellular networks don’t quite work like this. Your mobile data connection is actually a point-to-point tunnel to a gateway somewhere in the provider packet core, so you don’t really just “leak” multicast packets to other devices on the same cell. Even in many enterprise Wi-Fi networks, it’s quite common to see either client isolation or multicast filtering in place (in part because multicast traffic is often sent at a very low data rate and that can have unintended side effects).
acomjean 5y ago
That’s a interesting point (IPv6) My limited knowledge of multicast from working with network software a while ago was that it’s local network only, and udp and you needed to “subscribe” to get the broadcast messages. There was also a keep alive component which is a little different from normal UDP. I wrote a tool to help debug the system by subscribing and then dumping the messages. Perhaps this the problem Apple has with it? My understanding was a lot of routers didn’t support multicast, I know we had some issues with our network configuration. What happens on IPv6 is a interesting question. https://en.m.wikipedia.org/wiki/Multicast https://en.m.wikipedia.org/wiki/Multicast
aaaaaaaaaaab 5y ago
>so if apps can start sending tracking to "everyone" on the network (or a particular base station), could that cause problems. Then simply drop multicast packets? That's also what your ISP does with them.

neilalexander 5y ago

Cellular networks don’t quite work like this. Your mobile data connection is actually a point-to-point tunnel to a gateway somewhere in the provider packet core, so you don’t really just “leak” multicast packets to other devices on the same cell. Even in many enterprise Wi-Fi networks, it’s quite common to see either client isolation or multicast filtering in place (in part because multicast traffic is often sent at a very low data rate and that can have unintended side effects).

acomjean 5y ago

That’s a interesting point (IPv6) My limited knowledge of multicast from working with network software a while ago was that it’s local network only, and udp and you needed to “subscribe” to get the broadcast messages. There was also a keep alive component which is a little different from normal UDP. I wrote a tool to help debug the system by subscribing and then dumping the messages. Perhaps this the problem Apple has with it? My understanding was a lot of routers didn’t support multicast, I know we had some issues with our network configuration. What happens on IPv6 is a interesting question. https://en.m.wikipedia.org/wiki/Multicast https://en.m.wikipedia.org/wiki/Multicast

aaaaaaaaaaab 5y ago

>so if apps can start sending tracking to "everyone" on the network (or a particular base station), could that cause problems. Then simply drop multicast packets? That's also what your ISP does with them.