[arin-ppml] IPv6 Heretic thoughts

Dan White dwhite at olp.net
Fri Sep 5 15:51:15 EDT 2008

John Santos wrote:
> On Fri, 5 Sep 2008, Dan White wrote:
>> I think there's an implication in this line of reasoning that IPv6 is 
>> hard, and that dual stack is bad.
> I think there are 2 serious issues with this.  1) It doesn't immediately
> get you anything (with IPv4 runout) because each dual stacked host
> needs *TWO* addresses, an "easily obtainable" IPv6 address and a scarce
> IPv4 address.  

I don't grasp your point. Are you saying that it's a management problem 
of maintaining two addresses? Arguably, there is no end-user maintenance 
of IPv6 addresses (in a dual stack scenario).

> 2) Due to the way IPv6 defaults (apparently this is
> defined in the specifications), it tries an IPv6 connection 1st and
> then fails back to an IPv4 connection.

Not exactly. In the case where a user is visiting a website, the DNS 
resolver will do *one* search for IPv4 and IPv6 addresses for that site 
name. If there are no AAAA records for the site, no harm no foul. If an 
admin is advertising IPv6 services for a hostname that is not 
connectible that's a management issue, not a protocol deficiency.

> So it's not that dual-stacking is *bad*, but it just isn't too
> helpful until the infrastructure is up to snuff, and you can start
> introducing IPv6-only hosts.  But to support existing IPv4-only
> hosts, *all* publicly accessible servers will have to be dual-stacked
> for the forseeable future.

Dual stacking solves the problem of having IPv4 only hosts. It also 
conveniently solves the problem of having IPv6 only hosts. I do 
understand that there's a bit of a chicken and egg problem, but if you 
start dual stacking your hosts, you're at least prepared for what's coming.

- Dan

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