[dns-operations] Clear DNS cache

Edward Lewis ed.lewis at neustar.biz
Thu Jun 20 15:56:07 UTC 2013

On Jun 20, 2013, at 10:08, abang wrote:

> Am 20.06.2013 15:29, schrieb Vernon Schryver:
Quoting an earlier message:
>>>> "..It seems your nameservers don't agree on the SOA serial number!..."
>> I wouldn't put too much stock in what http://viewdns.info/ says
>> about anything...
> Yes of course. But in this case it is true.
> $ dig +short @ns1.linkedin.com linkedin.com. soa
> ns1.linkedin.com. hostmaster.linkedin.com. 2013061316 3600 600 604800 60
> $ dig +short @ns1.p43.dynect.net. linkedin.com. soa
> ns1.p43.dynect.net. hostmaster.linkedin.com. 2013061801 3600 600 604800 60

Think about the role of the SOA serial number.  It is used to manage the way AXFR (and Notify/IXFR) work.  We also know that AXFR is not the only way to move a zone between authoritative servers, for example, rsync of files.  So, the significance of the serial number is limited to situations that are relying on AXFR, and in other cases, the serial number may be interesting, but not important to proper protocol operation.

E.g., a cache does not know the serial number corresponding to most of the answers in the cache.  ("Most" - thinking about the cached SOA's and other cases like that [NCACHE].)

Edward Lewis             
NeuStar                    You can leave a voice message at +1-571-434-5468

There are no answers - just tradeoffs, decisions, and responses.

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