[zeromq-dev] IPv6 multicast RADIO/DISH

Lionel Flandrin lionel at svkt.org
Fri Apr 27 15:00:15 CEST 2018


On Fri, Apr 27, 2018 at 01:36:13PM +0100, Luca Boccassi wrote:
> On Fri, 2018-04-27 at 14:29 +0200, Lionel Flandrin wrote:
> > 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?
> 
> You can switch, I imagine it was done that way as it was quicker.
> Remember to add tests.

Got it, thanks.

I've already refactored the existing tests to add IPv6:

https://github.com/simias/libzmq/commit/16834fd4d2dee3460e3c46f44241e73f2a3633f8

I'm thinking about adding multicast tests as well but I wonder if
there are some caveats if I try to send and receive multicast traffic
in the test suite? Am I allowed to subscribe to a random multicast
address or is it forbidden to genererate external traffic in the
tests?

-- 
Lionel Flandrin
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