[zeromq-dev] IPv6 multicast RADIO/DISH

Lionel Flandrin lionel at svkt.org
Fri Apr 27 14:29:36 CEST 2018


On Thu, Apr 26, 2018 at 10:58:33AM +0100, Luca Boccassi wrote:
> On Thu, 2018-04-26 at 10:55 +0200, Lionel Flandrin wrote:
> > 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.
> 
> I'm not too familiar with that module - but it shouldn't be too much
> work. Address support is the first thing, and then the right socket
> options for V6 multicast in the engine I suppose:
> 
> https://github.com/zeromq/libzmq/blob/master/src/udp_address.cpp
> https://github.com/zeromq/libzmq/blob/master/src/udp_engine.cpp
> 
> Remember to add unit tests as the very first thing.

I've started doing that and I'm noticing that currently the UDP
addressing code uses inet_addr to parse the IPv4 address instead of
getaddrinfo like the TCP and PGM code. Is there a reason to avoid the
additional functionality of getaddrinfo here or can I safely switch to
it in the UDP code? Do we want to avoid resolving hostnames here for
some reason?

> > > 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,
> 
> IIRC both libraries should support IPv6 just fine. The manpage is just
> older - if you find it works and want to update it with some v6
> examples, feel free to send a PR.

-- 
Lionel Flandrin
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