在Google 公共 DNS 性能优势页面,他们声称
在 Google 公共 DNS 中,我们实施了多种方法来加快 DNS 查找时间。其中一些方法是相当标准的;其他方法是实验性的:
- 为所有用户提供全球覆盖。
但如果我们对他们的 IP 地址进行地理定位8.8.8.8和8.8.4.4我们看到他们是从山景城 (Mountain View) 得到服务的。
通过测量来自巴西的延迟,我发现
- 我的 ISP 的 DNS 在 13 毫秒内做出响应
- Google 的 DNS 在 20 毫秒内做出响应
- 开放DNS在旧金山平均 130 毫秒内回答
这怎么可能?如果 IP 路由方案指向加利福尼亚,他们怎么能从巴西的服务器进行响应呢?
答案1
地址只是拥有位于山景城的一家公司(谷歌公司)WHOIS 信息来自 ARIN。但它们的服务范围是 Google 决定宣布通往该范围的路线的任意位置。
对于他们的 DNS 服务器,Google 使用任播,而同样的地址实际上可以被路由到几个不同的位置:
在互联网上,任播通常是通过使用 BGP 从互联网上的许多不同位置同时通告相同的目标 IP 地址范围来实现的
这是该路由的 BGP 条目:
BGP routing table entry for 8.8.8.0/24, version 50533132
Paths: (18 available, best #12, table Default-IP-Routing-Table)
Not advertised to any peer
7018 15169, (received & used)
12.123.137.124 from 12.123.137.124 (12.123.137.124)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:37232
7018 15169, (received & used)
12.123.139.124 from 12.123.139.124 (12.123.139.124)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:34011
7018 15169, (received & used)
12.123.145.124 from 12.123.145.124 (12.123.145.124)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:33051
7018 15169, (received & used)
12.123.21.243 from 12.123.21.243 (12.123.21.243)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:39343
7018 15169, (received & used)
12.123.13.241 from 12.123.13.241 (12.123.13.241)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:32112
7018 15169, (received & used)
12.123.9.241 from 12.123.9.241 (12.123.9.241)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:38001
7018 15169, (received & used)
12.123.133.124 from 12.123.133.124 (12.123.133.124)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:36244
7018 15169, (received & used)
12.123.5.240 from 12.123.5.240 (12.123.5.240)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:34011
7018 15169, (received & used)
12.123.134.124 from 12.123.134.124 (12.123.134.124)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:36244
7018 15169, (received & used)
12.123.142.124 from 12.123.142.124 (12.123.142.124)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:33051
7018 15169, (received & used)
12.123.17.244 from 12.123.17.244 (12.123.17.244)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:36244
7018 15169, (received & used)
12.123.1.236 from 12.123.1.236 (12.123.1.236)
Origin IGP, localpref 100, valid, external, best
Community: 7018:2500 7018:37232
7018 15169, (received & used)
12.123.37.250 from 12.123.37.250 (12.123.37.250)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:36244
7018 15169, (received & used)
12.123.45.252 from 12.123.45.252 (12.123.45.252)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:32112
7018 15169, (received & used)
12.123.33.249 from 12.123.33.249 (12.123.33.249)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:39220
7018 15169, (received & used)
12.123.25.245 from 12.123.25.245 (12.123.25.245)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:34011
7018 15169, (received & used)
12.123.41.250 from 12.123.41.250 (12.123.41.250)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:37232
7018 15169, (received & used)
12.123.29.249 from 12.123.29.249 (12.123.29.249)
Origin IGP, localpref 100, valid, external
Community: 7018:2500 7018:33051