[zeromq-dev] IPv6 multicast RADIO/DISH

Lionel Flandrin lionel at svkt.org
Thu Apr 26 10:55:14 CEST 2018

On Thu, Apr 26, 2018 at 09:23:13AM +0100, Luca Boccassi wrote:
> On Thu, 2018-04-26 at 10:00 +0200, Lionel Flandrin wrote:
> > Hello everyone,
> > 
> > I'm trying to build a multicast protocol on top of an IPv6-only
> > network. I found that the draft RADIO/DISH sockets seem to do exactly
> > what I want, however the zmq_udp man page doesn't explicitely mention
> > supporting IPv6 multicast and I couldn't get pyzmq to bind an IPv6
> > multicast DISH with any URL format I've tried.
> > 
> > Is IPv6 multicast simply currently unsupported for UDP sockets? If
> > that's the case is it because of a technical difficulty or simply
> > because nobody bothered to implement it?
> > 
> > Thank you for your help (and your great library),
> UDP right now supports only ipv4 - it's a work in progress:
> https://github.com/zeromq/libzmq/issues/2891

Ah, I see, thank you for confirming that. Do you think adding IPv6
support would be a huge amount of work for somebody not familiar with
ZMQ's codebase? Is it just about adding a few branches changing
AF_INET to AF_INET6 or am I being ridiculously naive?

My current backup solution if I can't get ZMQ to do what I want is to
write my own IPv6 multicast code using BSD sockets directly, if
hacking ZMQ's code to add support is not too daunting I could consider
doing that instead.

> PUB/SUB with PGM or NORM should do what you are looking for.

I considered EPGM briefly but the zmq_pgm man page seems to say that
only IPv4 is supported, so I didn't even attempt it:

  A multicast address is specified by an IPv4 multicast address in its
  numeric representation.

Maybe I shoudln't have been so quick to dismiss it, I'm going to give
it a try. That being said I don't actually need the guarantees of
PGM/NORM, in particular I don't care if a frame gets mangled or
dropped and I don't need SNDMORE.

Thank you,
Lionel Flandrin
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