IPv6 Address allocation best practises for sites.

William Herrin bill at herrin.us
Mon Sep 24 23:37:31 UTC 2012

On Mon, Sep 24, 2012 at 6:52 PM, John Mitchell <mitch at illuminati.org> wrote:
> Question about what other service/network providers are doing in relation to
> allocation of addresses for websites.
> With IPv6 starting to trickle its way in, what is considered the industry
> best practise now for IP(v6) addresses bonded to websites. In the past the
> standard practise was to have a single IPv4 address shared between multiple
> sites using a name based virtual host directive in Apache/IIS, unless of
> course the site was SSL in which case it normally needed a IP of its own
> (unless you had a client who was happy to only support SSL on IE7+ browsers
> with SNI).
> Does the best practise switch to now using one IPv6 per site, or still the
> same one IPv6 for multi-sites?

Hi John,

Given web browser issues with javascript and DNS changes (see DNS
pinning) I'm not sure why you wouldn't want to pick a configuration
strategy where the IP could follow the site name from server to

I'm not in the multi-site web server business any more. The stuff I
build these days needs a load balancer. If I was I suspect I'd start
at routing a /64 to each web server. Then I'd take a long hard look at
whether it was a better plan to put all the multiply-addressed servers
on a single /64 and let neighbor discovery find the right one for each
site, or to implement /64''s per server and put /128 overrides in the
adjacent router for sites that move from the original server (because
the customer upgraded of course).

Then I'd consider whether to route a /112 to each server instead of a
/64 and assign a single /64 for the set of web servers.  I don't know
of any specific problem with routing 2^64 addresses to a single host
but I also can't imagine hosting more than 65,000 sites on a single

So, not a BCP but perhaps some food for thought when choosing your approach.

Bill Herrin

William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004

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