[zeromq-dev] zyre

[Pieter Hintjens]

I think the multicast filtering on access points counts as a bug in
the Android WiFi stack, simply. There's no inherent reason for it.
It's also difficult to work around except by using broadcast, which we
did.

It is possible to imagine Zyre working without bi-directional
discovery, so if A sees B, and connects to B, then B can connect back
to A even if it cannot see A's beacons. However we also use beacons
for heartbeating, as TCP is too inefficient. So we need this to work
both ways...

Since we introduced gossip discovery, however, it makes sense to
support multiple different discovery mechanisms. The calling app can
choose UDP broadcast if it wants that.

We could even tune this silently, e.g. use broadcast on WiFi, and
multicast on ethernet.

-Pieter

On Tue, Mar 24, 2015 at 11:17 AM, Arnaud Loonstra <arnaud at sphaero.org> wrote:
> I'm no Android guru but it might be logical. When the device becomes a
> hotspot it essentially becomes a router. It should then support the
> IGMP
> protocol. A broadcast it could simply forward anywhere. There's a
> question
> on SO:
> http://stackoverflow.com/questions/6550618/multicast-support-on-android-in-hotspot-tethering-mode
>
> No definite answer though.
>
> Even on a linux machine you have to do some configuration before it
> does
> multicast routing, i think.
>
> $ cat /proc/sys/net/ipv4/conf/all/mc_forwarding
> 0
>
> Arnaud
>
> On 2015-03-23 18:13, Pieter Hintjens wrote:
>> We used multicast first, and then switched to broadcast UDP because
>> the Android stack filters (or used to) incoming multicast when it is
>> running as an access point.
>>
>> On Mon, Mar 23, 2015 at 5:58 PM, Arnaud Loonstra <arnaud at sphaero.org>
>> wrote:
>>> "but I'm working on it in C nor Android"
>>>
>>> Add 'not' to that... I'm working on it in Python
>>>
>>> On 03/23/2015 04:05 PM, Arnaud Loonstra wrote:
>>>> Yes, but I'm working on it in C nor Android(currently):
>>>>
>>>> https://github.com/zeromq/pyre/blob/master/pyre/zbeacon.py#L208
>>>>
>
>
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