Re: [PATCH] Update getaddrinfo to RFC 6724 (bug 29496)
Adhemerval Zanella Netto <[email protected]> Thu, 30 Jul 2026 15:44:35 -0300
| Newsgroups | gmane.comp.lib.glibc.alpha |
|---|---|
| Organization | Linaro |
| Message-ID | <[email protected]> |
On 28/07/26 10:47, Andreas Schwab wrote:
> RFC 6724 is the successor of RFC 3484 and updated the default policy table
> and the address selection rules. The policy table contains more entries
> to depreference deprecated prefixes. The longest prefix match rule has
> been updated to only compare the prefix part of the addresses, so that
> addresses on the same subnet are no longer reordered.
I still reading about the RFC 6724 and our current implementation, and
reading the patch history I think Florian should be ok with the possible
deviations from rule 9.
I think this change should have a NEWS entry besides the bug fixing describing
what its does not implement from RFC.
> ---
> nss/Makefile | 7 +-
> nss/getaddrinfo.c | 107 ++++++++++++++---------
> nss/{tst-rfc3484-2.c => tst-rfc6724-2.c} | 6 +-
> nss/{tst-rfc3484-3.c => tst-rfc6724-3.c} | 4 +-
> nss/{tst-rfc3484-2.c => tst-rfc6724-4.c} | 51 ++++++-----
> nss/{tst-rfc3484.c => tst-rfc6724.c} | 6 +-
> posix/gai.conf | 48 +++++-----
> 7 files changed, 125 insertions(+), 104 deletions(-)
> copy nss/{tst-rfc3484-2.c => tst-rfc6724-2.c} (95%)
> rename nss/{tst-rfc3484-3.c => tst-rfc6724-3.c} (96%)
> rename nss/{tst-rfc3484-2.c => tst-rfc6724-4.c} (74%)
> rename nss/{tst-rfc3484.c => tst-rfc6724.c} (95%)
>
> diff --git a/nss/Makefile b/nss/Makefile
> index b1f25f0d71..3f57694fd7 100644
> --- a/nss/Makefile
> +++ b/nss/Makefile
> @@ -306,9 +306,10 @@ tests-static = tst-field
>
> tests-internal := \
> tst-field \
> - tst-rfc3484 \
> - tst-rfc3484-2 \
> - tst-rfc3484-3 \
> + tst-rfc6724 \
> + tst-rfc6724-2 \
> + tst-rfc6724-3 \
> + tst-rfc6724-4 \
> # tests-internal
>
> tests := \
> diff --git a/nss/getaddrinfo.c b/nss/getaddrinfo.c
> index 4f6ac3358a..2451dccaed 100644
> --- a/nss/getaddrinfo.c
> +++ b/nss/getaddrinfo.c
> @@ -1326,7 +1326,7 @@ static const struct prefixentry *labels;
> /* Default labels. */
> static const struct prefixentry default_labels[] =
> {
> - /* See RFC 3484 for the details. */
> + /* See RFC 6724 for the details. */
> { { .__in6_u
> = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01 } }
> @@ -1343,26 +1343,22 @@ static const struct prefixentry default_labels[] =
> = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00 } }
> }, 96, 4 },
> - /* The next two entries differ from RFC 3484. We need to treat
> - IPv6 site-local addresses special because they are never NATed,
> - unlike site-locale IPv4 addresses. If this would not happen, on
> - machines which have only IPv4 and IPv6 site-local addresses, the
> - sorting would prefer the IPv6 site-local addresses, causing
> - unnecessary delays when trying to connect to a global IPv6 address
> - through a site-local IPv6 address. */
> + { { .__in6_u
> + = { .__u6_addr8 = { 0x20, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> + }, 32, 5 },
> { { .__in6_u
> = { .__u6_addr8 = { 0xfe, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> - }, 10, 5 },
> + }, 10, 11 },
> { { .__in6_u
> - = { .__u6_addr8 = { 0xfc, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + = { .__u6_addr8 = { 0x3f, 0xfe, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> - }, 7, 6 },
> - /* Additional rule for Teredo tunnels. */
> + }, 16, 12 },
> { { .__in6_u
> - = { .__u6_addr8 = { 0x20, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + = { .__u6_addr8 = { 0xfc, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> - }, 32, 7 },
> + }, 7, 13 },
> { { .__in6_u
> = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> @@ -1376,23 +1372,39 @@ static const struct prefixentry *precedence;
> /* The default precedences. */
> static const struct prefixentry default_precedence[] =
> {
> - /* See RFC 3484 for the details. */
> + /* See RFC 6724 for the details. */
> { { .__in6_u
> = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01 } }
> }, 128, 50 },
> + { { .__in6_u
> + = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00 } }
> + }, 96, 35 },
> { { .__in6_u
> = { .__u6_addr8 = { 0x20, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> }, 16, 30 },
> { { .__in6_u
> - = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> - 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> - }, 96, 20 },
> + = { .__u6_addr8 = { 0x20, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> + }, 32, 5 },
> + { { .__in6_u
> + = { .__u6_addr8 = { 0xfc, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> + }, 7, 3 },
> { { .__in6_u
> = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> - 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x00, 0x00 } }
> - }, 96, 10 },
> + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> + }, 96, 1 },
> + { { .__in6_u
> + = { .__u6_addr8 = { 0xfe, 0xc0, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> + }, 10, 1 },
> + { { .__in6_u
> + = { .__u6_addr8 = { 0x3f, 0xfe, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> + 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> + }, 16, 1 },
> { { .__in6_u
> = { .__u6_addr8 = { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } }
> @@ -1469,7 +1481,7 @@ get_precedence (const struct sockaddr_in6 *in6)
> }
>
> static int
> -rfc3484_sort (const void *p1, const void *p2, void *arg)
> +rfc6724_sort (const void *p1, const void *p2, void *arg)
> {
> const size_t idx1 = *(const size_t *) p1;
> const size_t idx2 = *(const size_t *) p2;
> @@ -1632,6 +1644,8 @@ rfc3484_sort (const void *p1, const void *p2, void *arg)
> int bit1 = 0;
> int bit2 = 0;
>
> + /* Compute the common prefix length between source and destination
> + address. */
> if (a1->dest_addr->ai_family == PF_INET)
> {
> assert (a1->source_addr.sin6_family == PF_INET);
> @@ -1650,7 +1664,7 @@ rfc3484_sort (const void *p1, const void *p2, void *arg)
> in_addr_t netmask1 = 0xffffffffu << (32 - a1->prefixlen);
>
> if ((in1_src_addr & netmask1) == (in1_dst_addr & netmask1))
> - bit1 = stdc_leading_zeros (in1_dst_addr ^ in1_src_addr);
> + bit1 = a1->prefixlen;
>
> struct sockaddr_in *in2_dst
> = (struct sockaddr_in *) a2->dest_addr->ai_addr;
> @@ -1661,7 +1675,7 @@ rfc3484_sort (const void *p1, const void *p2, void *arg)
> in_addr_t netmask2 = 0xffffffffu << (32 - a2->prefixlen);
>
> if ((in2_src_addr & netmask2) == (in2_dst_addr & netmask2))
> - bit2 = stdc_leading_zeros (in2_dst_addr ^ in2_src_addr);
> + bit2 = a2->prefixlen;
> }
> else if (a1->dest_addr->ai_family == PF_INET6)
> {
> @@ -1680,20 +1694,33 @@ rfc3484_sort (const void *p1, const void *p2, void *arg)
>
> int i;
> for (i = 0; i < 4; ++i)
> - if (in1_dst->sin6_addr.s6_addr32[i]
> - != in1_src->sin6_addr.s6_addr32[i]
> - || (in2_dst->sin6_addr.s6_addr32[i]
> - != in2_src->sin6_addr.s6_addr32[i]))
> - break;
> -
> - if (i < 4)
> {
> - uint32_t set_bits1 = (in1_dst->sin6_addr.s6_addr32[i]
> - ^ in1_src->sin6_addr.s6_addr32[i]);
> - uint32_t set_bits2 = (in2_dst->sin6_addr.s6_addr32[i]
> - ^ in2_src->sin6_addr.s6_addr32[i]);
> - bit1 = stdc_leading_zeros (ntohl (set_bits1));
> - bit2 = stdc_leading_zeros (ntohl (set_bits2));
> + uint32_t mask1, mask2;
> + if (i * 32 >= a1->prefixlen)
> + mask1 = 0xffffffffu;
> + else if ((i + 1) * 32 > a1->prefixlen)
> + mask1 = 0xffffffffu >> (a1->prefixlen & 31);
> + else
> + mask1 = 0;
> + if (i * 32 >= a2->prefixlen)
> + mask2 = 0xffffffffu;
> + else if ((i + 1) * 32 > a2->prefixlen)
> + mask2 = 0xffffffffu >> (a2->prefixlen & 31);
> + else
> + mask2 = 0;
> + if (((in1_dst->sin6_addr.s6_addr32[i]
> + ^ in1_src->sin6_addr.s6_addr32[i]) & htonl (~mask1)) != 0
> + || ((in2_dst->sin6_addr.s6_addr32[i]
> + ^ in2_src->sin6_addr.s6_addr32[i]) & htonl (~mask2)) != 0)
> + {
> + bit1 = stdc_leading_zeros (ntohl (in1_dst->sin6_addr.s6_addr32[i]
> + ^ in1_src->sin6_addr.s6_addr32[i])
> + | mask1);
> + bit2 = stdc_leading_zeros (ntohl (in2_dst->sin6_addr.s6_addr32[i]
> + ^ in2_src->sin6_addr.s6_addr32[i])
> + | mask2);
> + break;
> + }
> }
> }
>
> @@ -1722,7 +1749,7 @@ in6aicmp (const void *p1, const void *p2)
> }
>
>
> -/* Name of the config file for RFC 3484 sorting (for now). */
> +/* Name of the config file for RFC 6724 sorting (for now). */
> #define GAICONF_FNAME "/etc/gai.conf"
>
>
> @@ -2407,7 +2434,7 @@ getaddrinfo (const char *name, const char *service,
> __libc_once_define (static, once);
> __typeof (once) old_once = once;
> __libc_once (once, gaiconf_init);
> - /* Sort results according to RFC 3484. */
> + /* Sort results according to RFC 6724. */
> struct sort_result *results;
> size_t *order;
> struct addrinfo *q;
> @@ -2579,11 +2606,11 @@ getaddrinfo (const char *name, const char *service,
> __libc_lock_lock (lock);
> if (__libc_once_get (old_once) && gaiconf_reload_flag)
> gaiconf_reload ();
> - __qsort_r (order, nresults, sizeof (order[0]), rfc3484_sort, &src);
> + __qsort_r (order, nresults, sizeof (order[0]), rfc6724_sort, &src);
> __libc_lock_unlock (lock);
> }
> else
> - __qsort_r (order, nresults, sizeof (order[0]), rfc3484_sort, &src);
> + __qsort_r (order, nresults, sizeof (order[0]), rfc6724_sort, &src);
>
> /* Queue the results up as they come out of sorting. */
> q = p = results[order[0]].dest_addr;
> diff --git a/nss/tst-rfc3484-2.c b/nss/tst-rfc6724-2.c
> similarity index 95%
> copy from nss/tst-rfc3484-2.c
> copy to nss/tst-rfc6724-2.c
> index 7f89e1527c..62b06cb8f1 100644
> --- a/nss/tst-rfc3484-2.c
> +++ b/nss/tst-rfc6724-2.c
> @@ -60,7 +60,7 @@ _res_hconf_init (void)
> #include "getaddrinfo.c"
>
> /* This is the beginning of the real test code. The above defines
> - (among other things) the function rfc3484_sort. */
> + (among other things) the function rfc6724_sort. */
>
>
> #if __BYTE_ORDER == __BIG_ENDIAN
> @@ -142,7 +142,7 @@ do_test (void)
>
>
> struct sort_result_combo combo = { .results = results, .nresults = 2 };
> - qsort_r (order, 2, sizeof (order[0]), rfc3484_sort, &combo);
> + qsort_r (order, 2, sizeof (order[0]), rfc6724_sort, &combo);
>
> int result = 0;
> if (results[order[0]].dest_addr->ai_family == AF_INET6)
> @@ -172,7 +172,7 @@ do_test (void)
> order[0] = 0;
>
>
> - qsort_r (order, 2, sizeof (order[0]), rfc3484_sort, &combo);
> + qsort_r (order, 2, sizeof (order[0]), rfc6724_sort, &combo);
>
> if (results[order[0]].dest_addr->ai_family == AF_INET6)
> {
> diff --git a/nss/tst-rfc3484-3.c b/nss/tst-rfc6724-3.c
> similarity index 96%
> rename from nss/tst-rfc3484-3.c
> rename to nss/tst-rfc6724-3.c
> index 23aebfd54a..fce34961fe 100644
> --- a/nss/tst-rfc3484-3.c
> +++ b/nss/tst-rfc6724-3.c
> @@ -60,7 +60,7 @@ _res_hconf_init (void)
> #include "getaddrinfo.c"
>
> /* This is the beginning of the real test code. The above defines
> - (among other things) the function rfc3484_sort. */
> + (among other things) the function rfc6724_sort. */
>
>
> #if __BYTE_ORDER == __BIG_ENDIAN
> @@ -139,7 +139,7 @@ do_test (void)
> }
>
> struct sort_result_combo combo = { .results = results, .nresults = naddrs };
> - qsort_r (order, naddrs, sizeof (order[0]), rfc3484_sort, &combo);
> + qsort_r (order, naddrs, sizeof (order[0]), rfc6724_sort, &combo);
>
> int result = 0;
> for (int i = 0; i < naddrs; ++i)
> diff --git a/nss/tst-rfc3484-2.c b/nss/tst-rfc6724-4.c
> similarity index 74%
> rename from nss/tst-rfc3484-2.c
> rename to nss/tst-rfc6724-4.c
> index 7f89e1527c..6f4f9974f1 100644
> --- a/nss/tst-rfc3484-2.c
> +++ b/nss/tst-rfc6724-4.c
> @@ -59,8 +59,10 @@ _res_hconf_init (void)
> #undef USE_NSCD
> #include "getaddrinfo.c"
>
> +nss_action_list __nss_hosts_database attribute_hidden;
> +
> /* This is the beginning of the real test code. The above defines
> - (among other things) the function rfc3484_sort. */
> + (among other things) the function rfc6724_sort. */
>
>
> #if __BYTE_ORDER == __BIG_ENDIAN
> @@ -86,33 +88,30 @@ do_test (void)
> precedence = default_precedence;
> scopes = default_scopes;
>
> - struct sockaddr_in so1;
> - so1.sin_family = AF_INET;
> - so1.sin_addr.s_addr = h (0xc0a85f19);
> - /* Clear the rest of the structure to avoid warnings. */
> - memset (so1.sin_zero, '\0', sizeof (so1.sin_zero));
> + struct sockaddr_in6 so1;
> + so1.sin6_family = AF_INET6;
> + so1.sin6_addr.s6_addr32[0] = h (0xfec01234);
> + so1.sin6_addr.s6_addr32[1] = 1;
> + so1.sin6_addr.s6_addr32[2] = 1;
> + so1.sin6_addr.s6_addr32[3] = 1;
>
> - struct sockaddr_in sa1;
> - sa1.sin_family = AF_INET;
> - sa1.sin_addr.s_addr = h (0xe0a85f19);
> + struct sockaddr_in6 sa1;
> + sa1.sin6_family = AF_INET6;
> + sa1.sin6_addr.s6_addr32[0] = h (0x07d10001);
> + sa1.sin6_addr.s6_addr32[1] = 1;
> + sa1.sin6_addr.s6_addr32[2] = 1;
> + sa1.sin6_addr.s6_addr32[3] = 1;
>
> struct addrinfo ai1;
> - ai1.ai_family = AF_INET;
> + ai1.ai_family = AF_INET6;
> ai1.ai_addr = (struct sockaddr *) &sa1;
>
> - struct sockaddr_in6 so2;
> - so2.sin6_family = AF_INET6;
> - so2.sin6_addr.s6_addr32[0] = h (0xfec01234);
> - so2.sin6_addr.s6_addr32[1] = 1;
> - so2.sin6_addr.s6_addr32[2] = 1;
> - so2.sin6_addr.s6_addr32[3] = 1;
> -
> struct sockaddr_in6 sa2;
> sa2.sin6_family = AF_INET6;
> sa2.sin6_addr.s6_addr32[0] = h (0x07d10001);
> sa2.sin6_addr.s6_addr32[1] = 1;
> sa2.sin6_addr.s6_addr32[2] = 1;
> - sa2.sin6_addr.s6_addr32[3] = 1;
> + sa2.sin6_addr.s6_addr32[3] = 2;
>
> struct addrinfo ai2;
> ai2.ai_family = AF_INET6;
> @@ -133,19 +132,19 @@ do_test (void)
>
> results[1].dest_addr = &ai2;
> results[1].got_source_addr = true;
> - results[1].source_addr_len = sizeof (so2);
> + results[1].source_addr_len = sizeof (so1);
> results[1].source_addr_flags = 0;
> results[1].prefixlen = 16;
> results[1].index = 0;
> - memcpy (&results[1].source_addr, &so2, sizeof (so2));
> + memcpy (&results[1].source_addr, &so1, sizeof (so1));
> order[1] = 1;
>
>
> struct sort_result_combo combo = { .results = results, .nresults = 2 };
> - qsort_r (order, 2, sizeof (order[0]), rfc3484_sort, &combo);
> + qsort_r (order, 2, sizeof (order[0]), rfc6724_sort, &combo);
>
> int result = 0;
> - if (results[order[0]].dest_addr->ai_family == AF_INET6)
> + if (order[0] != 0)
> {
> puts ("wrong order in first test");
> result |= 1;
> @@ -164,17 +163,17 @@ do_test (void)
>
> results[0].dest_addr = &ai2;
> results[0].got_source_addr = true;
> - results[0].source_addr_len = sizeof (so2);
> + results[0].source_addr_len = sizeof (so1);
> results[0].source_addr_flags = 0;
> results[0].prefixlen = 16;
> results[0].index = 0;
> - memcpy (&results[0].source_addr, &so2, sizeof (so2));
> + memcpy (&results[0].source_addr, &so1, sizeof (so1));
> order[0] = 0;
>
>
> - qsort_r (order, 2, sizeof (order[0]), rfc3484_sort, &combo);
> + qsort_r (order, 2, sizeof (order[0]), rfc6724_sort, &combo);
>
> - if (results[order[0]].dest_addr->ai_family == AF_INET6)
> + if (order[0] != 0)
> {
> puts ("wrong order in second test");
> result |= 1;
> diff --git a/nss/tst-rfc3484.c b/nss/tst-rfc6724.c
> similarity index 95%
> rename from nss/tst-rfc3484.c
> rename to nss/tst-rfc6724.c
> index f882f95f84..57bdc099b4 100644
> --- a/nss/tst-rfc3484.c
> +++ b/nss/tst-rfc6724.c
> @@ -60,7 +60,7 @@ _res_hconf_init (void)
> #include "getaddrinfo.c"
>
> /* This is the beginning of the real test code. The above defines
> - (among other things) the function rfc3484_sort. */
> + (among other things) the function rfc6724_sort. */
>
>
> #if __BYTE_ORDER == __BIG_ENDIAN
> @@ -89,7 +89,7 @@ static size_t order[naddrs];
>
> static int expected[naddrs] =
> {
> - 9, 4, 3, 6, 5, 7, 8, 2, 0, 1
> + 2, 3, 4, 5, 6, 7, 8, 9, 0, 1
> };
>
>
> @@ -131,7 +131,7 @@ do_test (void)
> }
>
> struct sort_result_combo combo = { .results = results, .nresults = naddrs };
> - qsort_r (order, naddrs, sizeof (order[0]), rfc3484_sort, &combo);
> + qsort_r (order, naddrs, sizeof (order[0]), rfc6724_sort, &combo);
>
> int result = 0;
> for (int i = 0; i < naddrs; ++i)
> diff --git a/posix/gai.conf b/posix/gai.conf
> index 4616ed005b..de76e2c26f 100644
> --- a/posix/gai.conf
> +++ b/posix/gai.conf
> @@ -1,7 +1,7 @@
> # Configuration for getaddrinfo(3).
> #
> # So far only configuration for the destination address sorting is needed.
> -# RFC 3484 governs the sorting. But the RFC also says that system
> +# RFC 6724 governs the sorting. But the RFC also says that system
> # administrators should be able to overwrite the defaults. This can be
> # achieved here.
> #
> @@ -16,40 +16,34 @@
> # used. There are possible runtime problems. The default is no.
> #
> # label <mask> <value>
> -# Add another rule to the RFC 3484 label table. See section 2.1 in
> -# RFC 3484. The default is:
> +# Add another rule to the RFC 6724 label table. See section 2.1 in
> +# RFC 6724. The default is:
> #
> #label ::1/128 0
> #label ::/0 1
> #label 2002::/16 2
> #label ::/96 3
> #label ::ffff:0:0/96 4
> -#label fec0::/10 5
> -#label fc00::/7 6
> -#label 2001:0::/32 7
> -#
> -# This default differs from the tables given in RFC 3484 by handling
> -# (now obsolete) site-local IPv6 addresses and Unique Local Addresses.
> -# The reason for this difference is that these addresses are never
> -# NATed while IPv4 site-local addresses most probably are. Given
> -# the precedence of IPv6 over IPv4 (see below) on machines having only
> -# site-local IPv4 and IPv6 addresses a lookup for a global address would
> -# see the IPv6 be preferred. The result is a long delay because the
> -# site-local IPv6 addresses cannot be used while the IPv4 address is
> -# (at least for the foreseeable future) NATed. We also treat Teredo
> -# tunnels special.
> +#label 2001::/32 5
> +#label fec0::/10 11
> +#label 3ffe::/16 12
> +#label fc00::/7 13
> #
> # precedence <mask> <value>
> -# Add another rule to the RFC 3484 precedence table. See section 2.1
> -# and 10.3 in RFC 3484. The default is:
> -#
> -#precedence ::1/128 50
> -#precedence ::/0 40
> -#precedence 2002::/16 30
> -#precedence ::/96 20
> -#precedence ::ffff:0:0/96 10
> -#
> -# For sites which prefer IPv4 connections change the last line to
> +# Add another rule to the RFC 6724 precedence table. See section 2.1
> +# and 10.3 in RFC 6724. The default is:
> +#
> +#precedence ::1/128 50
> +#precedence ::/0 40
> +#precedence ::ffff:0:0/96 35
> +#precedence 2002::/16 30
> +#precedence 2001::/32 5
> +#precedence fc00::/7 3
> +#precedence ::/96 1
> +#precedence fec0::/10 1
> +#precedence 3ffe::/16 1
> +#
> +# For sites which prefer IPv4 connections change the coresponding line to
> #
> #precedence ::ffff:0:0/96 100
>