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Re: lib/42405: libc: getaddrinfo() should perform T_A lookups before T_AAAA lookups, was: Resolver problems

On Fri, Dec 4, 2009 at 12:13 AM, Chuck Swiger <> wrote:
> [ ... Reply-to: set as Matt requested... ]
> On Dec 3, 2009, at 2:13 PM, Matthias Scheler wrote:
>> On Thu, Dec 03, 2009 at 11:05:11AM -0800, Chuck Swiger wrote:
>>> Trying to perform A lookups before you try AAAA lookups turns out to
>>> resolve almost all the problems users were experiencing,
>> It might cause new problems where IPv6 connectivity works better
>> than IPv4 e.g. because a NAT device on the network path is the bootleneck.
> Yes, it might. ÂI've yet to see a situation where that actually was the case, 
> however, but it's conceivable.
> A few years back, when I was working pretty actively on some 
> security/firewall products, I made the effort to write protocol-independant 
> code and avoid favoring IPv4 or IPv6. ÂI also hunted around and tried to find 
> an ISP which would route IPv6 traffic for me (this was in metro NYC area), 
> and was unable to find anyone willing to provide a T1/T3 which actually 
> routed IPv6; AT&T's MIS was considering an IPv6 pilot sometime a year or two 
> down the road...but aside from a 6in4 tunnel from Hurricane, there were quite 
> literally zero organizations willing to provide IPv6 connectivity.
> From
> "We can measure the percentage of networks running IPv6 by comparing the set 
> of ASes in the IPv6 routing table to those in the combined set of IPv4 and 
> IPv6.
> IPv4 and IPv6 RIBs Last Parsed: Thu Dec 3 00:12:04 PST 2009
> IPv4 ASes: 33215
> IPv6 ASes: 1815
> ASes using only IPv4: 31454
> ASes using only IPv6: 54
> ASes using IPv4 and IPv6: 1761
> ASes using IPv4 or IPv6: 33269
> Percentage of ASes (IPv4 or IPv6) running IPv6: 5.5%"
>>> ... and so this became the default behavior on FreeBSD
>> Can we please make this configurable instead of switch from one
>> arbitrary default value to another one?
> It's entirely reasonable to make this configurable, although for the original 
> circumstance Ingolf describes, where "v6 support has already been removed 
> from my kernel -- no interface has a v6 address", it's hardly arbitrary for 
> an IPv4-only system to try A lookups before hoping that an AAAA lookup will 
> return something (and that an IPv4-to-IPv6 tunnel will be available, also).
> For that matter, with 0.16% of routable networks IPv6-only, 5.29% 
> dual-protocol capable, and 94.54% of IPv4-only, I don't feel it is arbitrary 
> to choose to perform A before AAAA by default. ÂAnyway, by all means, please 
> submit a better solution and update 
> accordingly. Â
> :-)

I don't think that we should default to anything 4 over 6. ipv4 is a
dead horse and
it will soon silently disappear like floppy drives and VHS. :)

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