TTL Caching

[Tim Maestas]

	I've got a question regarding the caching of TTL's I'm 
	hoping someone can clarify.  We've been arguing this with
	Microsoft, and low and behold, they quoted rfc2181, section 8.
	Specifically, this paragraph:


  "Implementations are always free to place an upper bound on any TTL
   received, and treat any larger values as if they were that upper
   bound.  The TTL specifies a maximum time to live, not a mandatory
   time to live."

	The problem is that the caching resolver in Win2k seems to be
	broken, caching records with CNAMEs incorrectly.  MS acknowledged
	this, and gave us a fix.  However it still seemed as if their 
	implementation was broken.  We have a CNAME record, with a 3600
	TTL.  The canonical name it references has a 1 second TTL.  MS
	Win2k resolver caches both records with a 1 second TTL.  They say
	that acording to rfc2181 this is legal, as the TTL is really only
	a maximum time to live, and they are not required to cache what
	the DNS server returns.  Is this correct?

	(BTW, the original problem, with unpatched Win2k, was that the 
	A record of the canonical name referenced in the CNAME RR was
	cached with the TTL of the CNAME.  Basically their fix just
	reversed this behaviour, resulting in what I explained above).
-Tim

------------------------------------------
http://www.dnsconsultants.com
DNS and other network consulting
------------------------------------------