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Re: Multihoming an end user

On Sun, Sep 25, 2005 at 02:30:07PM -0400, Chris Wagner wrote:
> At 12:56 PM 9/25/05 +0300, Juha-Matti Tapio wrote:
> >Correctly working caches do not grow the TTL. If the original DNS server
> >says that the TTL is 60 seconds then all caches should obey it. In my
> >experience most caches work correctly with regards to TTL so that 60 seconds
> >will not be magically multiplied to three minutes.
> But won't each cache set it's own TTL to 60.?  So each cache retrieval will
> start a new 60 second timer even though the source could be near the end of
> the TTL.  So an nth degree cache could be n x 60 out of sync.

The original server gives the TTL 60. When the second level cache server is
queried again 10 seconds later, it knows that the TTL is now only 50 and
gives that as a response. Each cache sets the timer to what it gets from
query results _but_ the cache gives to it's clients the value of the TTL
that is remaining.

An example with my local cache:

$ dig +noquestion +nocomments +nostats klecker.debian.org; sleep 10; \
  dig +noquestion +nocomments +nostats klecker.debian.org

; <<>> DiG 9.2.4 <<>> +noquestion +nocomments +nostats klecker.debian.org
;; global options:  printcmd
klecker.debian.org.     3250    IN      A
debian.org.             2857    IN      NS      klecker.debian.org.
debian.org.             2857    IN      NS      saens.debian.org.
debian.org.             2857    IN      NS      spohr.debian.org.
debian.org.             2857    IN      NS      samosa.debian.org.
samosa.debian.org.      2857    IN      A

; <<>> DiG 9.2.4 <<>> +noquestion +nocomments +nostats klecker.debian.org
;; global options:  printcmd
klecker.debian.org.     3240    IN      A
debian.org.             2847    IN      NS      spohr.debian.org.
debian.org.             2847    IN      NS      samosa.debian.org.
debian.org.             2847    IN      NS      klecker.debian.org.
debian.org.             2847    IN      NS      saens.debian.org.
samosa.debian.org.      2847    IN      A

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