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Re: Geographic map of IPv6 availability

  • From: Mark Andrews
  • Date: Mon Oct 15 17:40:30 2007

In article <[email protected]> you write:
>On 10/15/07, Mark Andrews <[email protected]> wrote:
>> In article <[email protected]> you write:
>> >
>> >
>> >On 15/10/2007, at 8:24 PM, Martin Hannigan wrote:
>> >
>> >> [moresnip]
>> >>
>> >> The way I read the portion of the thread related to resolver behavoir
>> >> was that the resolver behavior was being discussed. Not the client.
>> >> The resolver should have an attribute to select the preference between
>> >> A vs. AAAA. Otherwise, it's setting network policy through code.
>> >>
>> >> My question was if there is an option to adjust this, where is it? I
>> >> don't see it. I'm not a BIND uber-expert. If there is no option, there
>> >> quite possibly ought to be one.
>> >
>> >I guess the question could also be asked as to whether BIND honours
>> >the host's configuration of the address selection policy - which
>> >seems more likely than implementing it itself.
>> >
>> >For those who missed it - OS level address selection policy won't
>> >apply to BIND without specific code, as BIND is a recursive resolver
>> >so won't be calling getaddrinfo(3).
>> >
>> >--
>> >Nathan Ward
>> named actually measures the response times to individual addresses
>> and uses those to determine which servers to query.  Named also
>> uses what addresses it has before attempting to determine if there
>> are alternate addresses.
>> Address selection policies are kind of meaningless in this environment.
>How so? I think it's valuable to be able to decide for myself if I
>want preference for AAAA or A. If I understand what I am reading, and
>am properly recalling past threads here, this would seem important
>since it affects the user experience.
>As far as how it sets network policy goes, any time something sets a
>preferred mode over other options and is not modifiable, it's akin to
>setting policy. History has shown that most of us agree with this.
>If I'm not interpreting this correctly, I'm all ears (eyes).
>[ Note, I'm not making any assumption that anyone has set out to set
>internet policy through software. ]

	getaddrinfo() is based on the assumption that there is *not*
	a cache response times etc.  named builds such a cache.  To
	do that however it needs to actually query the addresses.
	It also has to have all the addresses to make that

	Named works with partial information rather than going out
	and fetching complete information then making the query.
	Doing that would slow down the resolution process.

	Most applictions also make exactly one connection and making
	sure that is optimal is useful.  Named makes millions of
	connections.  It's a completely different class of application.

	Named is also pretty much agnostic about whether IPv4 or
	IPv6 transport is used.  At the moment it still tends to
	be IPv4 as there is very little AAAA glue even when there
	are AAAA records for the nameserver.