[zeromq-dev] [PATCH] IPv4/IPv6 wiring for 3.0

Steven McCoy steven.mccoy at miru.hk
Mon Aug 8 09:09:14 CEST 2011

On 8 August 2011 14:46, Martin Sustrik <sustrik at 250bpm.com> wrote:

> On 08/08/2011 06:33 AM, Steven McCoy wrote:
>  Conclusion:
>>    * Within 0mq use IPv6 sockets by default unless the platform has
>>      only IPv4 support.
>>    * Drop down to IPv4 sockets if the option ZMQ_IPV4ONLY is set.
>>    * Force dual-stack behaviour in order to enumerate IPv4 interfaces
>>      for binding.
> I like that. AFAICS it would work as follows:
> 1. IPv4 server & IPv4 client - use IPv4
> 2. IPv4 server & IPv6 client - when calling getaddrinfo, client will get
> IPv4-in-IPv6 address, the communication will happen in IPv4
> 3. IPv6 server & IPv4 client - when client connects to the server, server
> will get IPv4-in-IPv6 address, the communication will happen in IPv4
> 4. IPv6 server & IPv6 clinet - use IPv6
> The only problem I see is IPv6 server and IPv6 client over Internet. If
> there's a lack of IPv6 support on the path (ISPs and so on), the won't be
> able to speak each to another. The only way to make it work would be to set
> ZMQ_IP4ONLY option on at least one side.
> Given the current state of IPv4-to-IPv6 transition, wouldn't it be wise to
> switch ZMQ_IP4ONLY on by default?
That's what beta testing is for :-)

Most system admins use IP addresses because DNS is a single point of failure
within an organisation so the option would have no impact for them.

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