10.6. Configuring ULA Preference (配置 ULA 偏好)

10.6. Configuring ULA Preference (配置 ULA 偏好)

RFC 5220 [RFC5220] 的第 2.1.4, 2.2.2 和 2.2.3 节描述了与唯一本地地址 (Unique Local Addresses, ULA) [RFC4193] 相关的地址选择问题。默认情况下, 全局 IPv6 目标优先于 ULA 目标, 因为任意 ULA 不一定是可达的:

Candidate Source Addresses: 2001:db8:1::1 or fd11:1111:1111:1::1
Destination Address List: 2001:db8:2::2 or fd22:2222:2222:2::2
Result: 2001:db8:2::2 (src 2001:db8:1::1) then fd22:2222:2222:2::2 (src fd11:1111:1111:1::1) (prefer higher precedence)

然而, 可以使用站点特定的策略条目来使站点内的 ULA 优先于全局地址, 如下所示。

   Prefix        Precedence Label
   ::1/128               50     0
   fd11:1111:1111::/48   45    14
   ::/0                  40     1
   ::ffff:0:0/96         35     4
   2002::/16             30     2
   2001::/32              5     5
   fc00::/7               3    13
   ::/96                  1     3
   fec0::/10              1    11
   3ffe::/16              1    12

这样的配置将产生以下效果:

Candidate Source Addresses: 2001:db8:1::1 or fd11:1111:1111:1::1
Destination Address List: 2001:db8:2::2 or fd22:2222:2222:2::2
Unchanged Result: 2001:db8:2::2 (src 2001:db8:1::1) then fd22:2222:2222:2::2 (src fd11:1111:1111:1::1) (prefer higher precedence)

Candidate Source Addresses: 2001:db8:1::1 or fd11:1111:1111:1::1
Destination Address List: 2001:db8:2::2 or fd11:1111:1111:2::2
New Result: fd11:1111:1111:2::2 (src fd11:1111:1111:1::1) then 2001:db8:2::2 (src 2001:db8:1::1) (prefer higher precedence)

由于 ULA 被定义为具有 /48 站点前缀, 实现可能选择在具有 ULA 的机器上自动添加这样的行。

还值得注意的是, ULA 被分配全局范围。因此, 前缀策略表中存在一行或多行很重要, 以便源地址选择不会纯粹基于最长匹配来选择 ULA:

Candidate Source Addresses: 2001:db8:1::1 or fd11:1111:1111:1::1
Destination Address List: ff00:1
Result: 2001:db8:1::1 (prefer matching label)