does Varnish (between nginx frontend and apache backend) need separate instances/listeners for IPv4/6 dual-stack use?

Kristian Lyngstol kristian at
Fri May 20 07:26:46 CEST 2011

On Wed, May 18, 2011 at 08:13:05AM -0700, d1+varnish at wrote:
> Hi
> On Wed, 18 May 2011 12:08 +0200, "Kristian Lyngstol"
> <kristian at> wrote:
> > Varnish will listen to both IPv4 and IPv6 if available. It will also
> > talk to backends using both ipv4 and ipv6. It currently prefers ipv4 for
> > backend communication if the supplied hostname resolves to both ipv4 and
> > ipv6, which is configurable via the prefer_ipv6 param.
> > 
> > Varnish more or less Just Works with IPv6.
> I understand that Varnish CAN listen at ipv4/ipv6.  I'm still unclear as
> to what SHOULD be done in this stack.
> Are you suggesting that this is sufficient?


>  varnish listening ONLY on IPv4 (launched as ... -a <IPv4>:port1 -T
>  <IPv4>:port2 ...)


What you set up is up to you.

I don't know why you'd ever want Varnish to only speak IPv4, but I don't
know your architecture.

What Varnish should and shouldn't do in this regards is up to you, not
Varnish, since Varnish is happy either way.

- Kristian

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