| This Parallels Something AOL Was Doing Ten Years Ago.....Any 90's era DHTML vetrans remember how over-aggressively AOL would cache www content, so it could serve its subscribers stale pages from its own caching proxies?
Deja vu! Google's first "line of defense" in keeping all the traffic hitting www.google.com flowing smoothly, is apparently being done at the DNS level. Right at the start, if you "ping www.google.com" you're using the first of 4 shuffled IP addresses your DNS server is supplied with when you ask it "what IP address does www.google.com point to":
~ > dig www.google.com a
; <<>> DiG 9.4.0 <<>> www.google.com a
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 19479
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 13, ADDITIONAL: 0
;; QUESTION SECTION:
;www.google.com. IN A
;; ANSWER SECTION:
www.google.com. 604165 IN CNAME www.l.google.com.
www.l.google.com. 148 IN A 74.125.19.99
www.l.google.com. 148 IN A 74.125.19.104
www.l.google.com. 148 IN A 74.125.19.147
www.l.google.com. 148 IN A 74.125.19.103
~ > dig www.google.com a
;; ANSWER SECTION:
www.google.com. 604148 IN CNAME www.l.google.com.
www.l.google.com. 131 IN A 74.125.19.103
www.l.google.com. 131 IN A 74.125.19.99
www.l.google.com. 131 IN A 74.125.19.104
www.l.google.com. 131 IN A 74.125.19.147
That's apparently group "L", so there's probably 11 other sets of four, maybe more.
WORTH NOTING: Each of those four expire in 131 seconds, meaning, those are supposed to be flushed from my DNS' cache after that, a subsequent query will force it to "get off its ass" and ask Google again.
Enter Comcast. Their DNS servers are so f(reak)ing "lazy", if a domain (www.karels.org, for one) is not in their cache, it won't even bother to look it up. Mix that with what Google does, and guess what!
-NK |
 dddane
join:2002-01-10
Chicago, IL | pretty much any major web site will have round robin servers set up in DNS like this... this inheritantly causes no problems, and really has no bearing on whether the page you get is cached or not...
if what you're saying about comcasts' dns servers not looking up entries it doesn't know, that's pretty pathetic on their part and i'm not sure why anyone would do business with them if they had a choice. |
| reply to DOStradamus
This is not a problem. www CNAME has a 7-day TTL.
www.google.com. 7D www.l.google.com.
Web farm for www.l.google.com has TTL of 5 mins. If they need to swap out a box from the farm, propagation will take 5 mins. That's all there's to it. Yahoo web farm has TTL of 1 mins, for example.
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"In a fight between you and the world, bet on the world." - Franz Kafka |
