
在Google 公共 DNS 效能優勢頁面,他們聲稱
在 Google 公共 DNS 中,我們實作了多種方法來加快 DNS 查找時間。其中一些方法相當標準;另一些則是相當標準的。其他是實驗性的:
- 提供全球覆蓋範圍以接近所有用戶。
但如果我們對他們的 IP 位址進行地理定位8.8.8.8和8.8.4.4我們看到他們是從山景城提供服務的。
測量來自巴西的延遲我發現
- 我的 ISP 的 DNS 在 13 毫秒內給出答复
- Google 的 DNS 在 20 毫秒內給出答案
- 開放DNS在舊金山平均 130 毫秒內給答案
這怎麼可能?如果 IP 路由方案通往加州,他們如何從巴西的伺服器進行回應?
答案1
地址只是擁有者據報道,位於山景城的一家公司(Google公司)世界衛生組織訊息來自阿林。但無論谷歌決定宣布從哪個位置到該範圍的路線,都可以為它們提供服務。
對於他們的 DNS 伺服器,Google 使用選播,並且相同的位址實際上可以路由到多個不同的位置:
在Internet上,選播通常是透過BGP來實現的,從Internet上的許多不同地方同時通告相同的目的IP位址範圍
這是該路由的 BGP 條目:
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