75 lines
3.4 KiB
Diff
75 lines
3.4 KiB
Diff
Pending acceptance upstream when this gets RFC'd:
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http://sourceware.org/bugzilla/show_bug.cgi?id=11438
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--- posix/gai.conf~ 2010-04-20 13:05:50.197813000 +0200
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+++ posix/gai.conf 2010-04-20 13:08:46.472675000 +0200
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@@ -66,3 +66,68 @@
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#scopev4 ::ffff:172.16.0.0/108 5
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#scopev4 ::ffff:192.168.0.0/112 5
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#scopev4 ::ffff:0.0.0.0/96 14
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+
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+
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+# Back in 2003, the sorting algorithm used by getaddrinfo() was defined in RFC
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+# 3484. However, this document did not take into account (or foresee) the
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+# ubiquity of IPv4 NAT on today's internet. This in turn causes some real
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+# operational problems that's hindering the deployment of IPv6 for content
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+# providers.
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+#
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+# The problem scenario is the following:
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+#
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+# An end user is located in a network numbered with private (RFC 1918) IPv4
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+# addresses and transitional 6to4 (RFC 3056) IPv6 addresses. The network is
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+# connected to the internet by a CPE/SOHO device implementing NAT for IPv4 and
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+# anycasted 6to4 (RFC 3068) for IPv6.
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+#
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+# When the user attempts to connect to a server whose hostname has both IPv4
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+# and IPv6 addresses published in DNS, an IPv6 connection using the
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+# transitional 6to4 service will be preferred. This happens because the scope
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+# comparsion fails for IPv4, the RFC 1918 addresses are assumed to have
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+# site-local scope, which is smaller than the global scope of the server's IPv4
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+# address. For IPv6, both the server's and the client's (6to4) address have
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+# global scope.
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+#
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+# Unfortunately, the operational reality is that a transitional technique such
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+# as 6to4 is much less reliable than IPv4. The relay routers might be located
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+# far away from the optimal IPv4 path, and thus cause a significant latency
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+# increase, or they might not even work optimally (they're usually operated by
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+# voulenteering third parties on a best-effort basis), and finally some ISPs
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+# simply filter away all proto-41 traffic. Transitional techniques are useful
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+# to give end users with IPv4-only service a real shot at accessing IPv6-only
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+# content, but it should never be preferred over IPv4 service when accessing
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+# dual-stacked content.
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+#
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+# RFC 3484 even acknowledges this, by saying to "<22>avoid the use of transitional
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+# addresses when native addresses are available"<22>.
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+#
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+# An IETF draft document which describes the problem in a much more detailed
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+# manner than I have is available here:
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+#
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+# http://tools.ietf.org/html/draft-denis-v6ops-nat-addrsel-00
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+#
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+# There's also an IETF draft that aims to revise RFC 3484 in order to fix this
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+# problem (amongst others):
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+#
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+# http://tools.ietf.org/html/draft-arifumi-6man-rfc3484-revise-02
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+#
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+# Quoting from this document:
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+#
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+# > 2.7. To change private IPv4 address scope
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+# >
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+# > As detailed in Remi's draft [I-D.denis-v6ops-nat-addrsel], when a
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+# > host is in NATed site, and has a private IPv4 address and
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+# > transitional addresses like 6to4 and Teredo, the host chooses
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+# > transitional IPv6 address to access most of the dual-stack servers.
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+# >
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+# > This is because private IPv4 address is defined to be site-local
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+# > scope, and as in RFC 3484, the scope matching rules (Rule 2) set
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+# > lower priority for private IPv4 address.
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+# >
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+# > By changing the address scope of private IPv4 address to global, this
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+# > problem can be solved.
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+
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+scopev4 ::ffff:10.0.0.0/104 14
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+scopev4 ::ffff:172.16.0.0/108 14
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+scopev4 ::ffff:192.168.0.0/112 14
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