On 09.12.13 16:37, sumsum 2000 wrote:
What i meant was that,
when a DNS query is made to emp.bbci.co.uk, the record for it is present
in the cache with TTL of 436. and since it is present, there should not be
any query to the DNS server,the same goes for emp-live.bbc.net.uk and
emp.bbci.co.uk.edgesuite.net
emp.bbci.co.uk. 436 IN CNAME emp-live.bbc.net.uk.
emp-live.bbc.net.uk. 253 IN CNAME emp.bbci.co.uk.edgesuite.net.
emp.bbci.co.uk.edgesuite.net. 3368 IN CNAME a336.g.akamai.net.
For all these three CNAME, there should not be any lookup that needs to
be sent to the DNS server, as they are present in the cache and their TTL
entries have not expired and are present in the cache. Only when it comes
to the last chain a336.g.akamai.net, which expires after TTL of 6 and when
is not present in the cache, the DNS query for this should be sent for
lookup.
But I see that though the entries for CNAME's are present in the cache,
the look up happens again for the CNAME,
how do you know? do they appear again with higher TTL? Did you sniff the
network to see they are looked up again?
it looks correct here:
uhlar@fantomas% dig +noauth +noadd +nostats +nocmd +nocomments emp.bbci.co.uk.
;emp.bbci.co.uk. IN A
emp.bbci.co.uk. 796 IN CNAME emp-live.bbc.net.uk.
emp-live.bbc.net.uk. 196 IN CNAME emp.bbci.co.uk.edgesuite.net.
emp.bbci.co.uk.edgesuite.net. 2632 IN CNAME a336.g.akamai.net.
a336.g.akamai.net. 10 IN A 80.239.149.26
a336.g.akamai.net. 10 IN A 80.239.247.14
uhlar@fantomas% dig +noauth +noadd +nostats +nocmd +nocomments emp.bbci.co.uk.
;emp.bbci.co.uk. IN A
emp.bbci.co.uk. 740 IN CNAME emp-live.bbc.net.uk.
emp-live.bbc.net.uk. 140 IN CNAME emp.bbci.co.uk.edgesuite.net.
emp.bbci.co.uk.edgesuite.net. 2576 IN CNAME a336.g.akamai.net.
a336.g.akamai.net. 20 IN A 80.239.149.26
a336.g.akamai.net. 20 IN A 80.239.247.14
--
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