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

[Chuck Swiger <cswiger%mac.com@localhost>]

[ ... Reply-to: tech-net%netbsd.org@localhost 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.  I'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.  I 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 http://bgp.he.net/ipv6-progress-report.cgi

"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.  Anyway, by all means, please submit a better 
solution and update 
http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=42405 accordingly.  :-)

Regards,
-- 
-Chuck