DNS/TTL0/case1について、ここに記述してください。
> From: John Orthoefer <jco@direwolf.com> > Date: February 7, 2009 8:23:16 AM EST > To: Marco Marongiu <brontolinux@gmail.com> > Cc: sage-members@sage.org > Subject: Re: [SAGE] DNS TTL question > > The only TTL value that is bad, is zero. > When I was at Genuity we > had Cisco Distributed Director (Which tried to give you the > "closest" active server to you, where closest had a lot of different > metrics.) At any rate, by default it gave out TTLs of zero, meaning > don't cache.
TTL 0 を異なる意味に使っているサーバがあるらしい。
> But it seems different servers had different ideas > about what TTL of zero means (worst was Microsoft's DNS server, > which apparently thought zero meant don't give this out as this > answer is expired.)
> However, 1 was fine. It would pass the answer > to the client and then promptly forget the answer.
> As I recall some brand of DNS server also thought zero means NEVER > expire.
こんな解釈をするサーバもあったらしい。 ひどすぎ。
> Most DNS caches have a way to set minimum/maxium TTLs. And there > is nothing you can do about that. You are telling them how long to > cache the answer with the TTL. And if people/servers don't listen > really nothing you can do about. > > To echo what others are saying. I typically set the TTL down > 300/600 when I want things to expire fast. Just remember to do it > well ahead of If you TTL is set to 3 days, and you set it down to > 600s an hour before the move, you still have people who 71hours left > on the old records. > > A good example is like www.microsoft.com, which uses Akamai. Which > uses something akin to Cisco DD to direct you to the nearest cache. > > ;; ANSWER SECTION: > www.microsoft.com. 3600 IN CNAME toggle.www.ms.akadns.net. > toggle.www.ms.akadns.net. 300 IN CNAME g.www.ms.akadns.net. > g.www.ms.akadns.net. 300 IN CNAME lb1.www.ms.akadns.net. > lb1.www.ms.akadns.net. 300 IN A 65.55.21.250 > > My advice use 300/600. > > johno