Since they may have cached the NS records at any time, it's just a
maximum of 345600. Once a device follows the delegation from the .com
authority and queries <a href="http://ns1.google.com/" target="_blank">ns1.google.com</a>
directly, the NS records in the cache that were learned from the .com
level servers are overwritten with what was learned from <a href="http://ns1.google.com/" target="_blank">ns1.google.com</a>.
The NS records from the TLD authority typically only exist within a
cache for a brief period until overwritten by first query response from the actual authority.<br><br><br><div class="gmail_quote">On Fri, Jan 16, 2009 at 10:56 AM, jittinan suwanrueangsri <span dir="ltr"><<a href="mailto:jittinan2@gmail.com">jittinan2@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div>Hi all</div>
<div> </div>
<div>This is result of tracing <a href="http://www.google.com/" target="_blank">www.google.com</a> by dig 9.5.0</div>
<div> </div>
<div>; <<>> DiG 9.5.0-P1 <<>> +trace <a href="http://www.google.com/" target="_blank">www.google.com</a><br>;; global options: printcmd<br>. 9398 IN NS <a href="http://E.ROOT-SERVERS.NET" target="_blank">E.ROOT-SERVERS.NET</a>.<br>
. 9398 IN NS <a href="http://G.ROOT-SERVERS.NET" target="_blank">G.ROOT-SERVERS.NET</a>.<br>. 9398 IN NS <a href="http://K.ROOT-SERVERS.NET" target="_blank">K.ROOT-SERVERS.NET</a>.<br>
. 9398 IN NS <a href="http://L.ROOT-SERVERS.NET" target="_blank">L.ROOT-SERVERS.NET</a>.<br>. 9398 IN NS <a href="http://A.ROOT-SERVERS.NET" target="_blank">A.ROOT-SERVERS.NET</a>.<br>
. 9398 IN NS <a href="http://J.ROOT-SERVERS.NET" target="_blank">J.ROOT-SERVERS.NET</a>.<br>. 9398 IN NS <a href="http://B.ROOT-SERVERS.NET" target="_blank">B.ROOT-SERVERS.NET</a>.<br>
. 9398 IN NS <a href="http://I.ROOT-SERVERS.NET" target="_blank">I.ROOT-SERVERS.NET</a>.<br>. 9398 IN NS <a href="http://D.ROOT-SERVERS.NET" target="_blank">D.ROOT-SERVERS.NET</a>.<br>
. 9398 IN NS <a href="http://F.ROOT-SERVERS.NET" target="_blank">F.ROOT-SERVERS.NET</a>.<br>. 9398 IN NS <a href="http://M.ROOT-SERVERS.NET" target="_blank">M.ROOT-SERVERS.NET</a>.<br>
. 9398 IN NS <a href="http://C.ROOT-SERVERS.NET" target="_blank">C.ROOT-SERVERS.NET</a>.<br>. 9398 IN NS <a href="http://H.ROOT-SERVERS.NET" target="_blank">H.ROOT-SERVERS.NET</a>.<br>
;; Received 272 bytes from 10.10.10.101#53(10.10.10.101) in 0 ms</div>
<div>com. 172800 IN NS <a href="http://a.gtld-servers.net" target="_blank">a.gtld-servers.net</a>.<br>com. 172800 IN NS <a href="http://b.gtld-servers.net" target="_blank">b.gtld-servers.net</a>.<br>
com. 172800 IN NS <a href="http://c.gtld-servers.net" target="_blank">c.gtld-servers.net</a>.<br>com. 172800 IN NS <a href="http://d.gtld-servers.net" target="_blank">d.gtld-servers.net</a>.<br>
com. 172800 IN NS <a href="http://e.gtld-servers.net" target="_blank">e.gtld-servers.net</a>.<br>com. 172800 IN NS <a href="http://f.gtld-servers.net" target="_blank">f.gtld-servers.net</a>.<br>
com. 172800 IN NS <a href="http://g.gtld-servers.net" target="_blank">g.gtld-servers.net</a>.<br>com. 172800 IN NS <a href="http://h.gtld-servers.net" target="_blank">h.gtld-servers.net</a>.<br>
com. 172800 IN NS <a href="http://i.gtld-servers.net" target="_blank">i.gtld-servers.net</a>.<br>com. 172800 IN NS <a href="http://j.gtld-servers.net" target="_blank">j.gtld-servers.net</a>.<br>
com. 172800 IN NS <a href="http://k.gtld-servers.net" target="_blank">k.gtld-servers.net</a>.<br>com. 172800 IN NS <a href="http://l.gtld-servers.net" target="_blank">l.gtld-servers.net</a>.<br>
com. 172800 IN NS <a href="http://m.gtld-servers.net" target="_blank">m.gtld-servers.net</a>.<br>;; Received 492 bytes from 199.7.83.42#53(<a href="http://L.ROOT-SERVERS.NET" target="_blank">L.ROOT-SERVERS.NET</a>) in 273 ms</div>
<div><font color="#ff0000"><a href="http://google.com" target="_blank">google.com</a>. 172800 IN NS <a href="http://ns1.google.com" target="_blank">ns1.google.com</a>.<br></font><a href="http://google.com" target="_blank">google.com</a>. 172800 IN NS <a href="http://ns2.google.com" target="_blank">ns2.google.com</a>.<br>
<a href="http://google.com" target="_blank">google.com</a>. 172800 IN NS <a href="http://ns3.google.com" target="_blank">ns3.google.com</a>.<br><a href="http://google.com" target="_blank">google.com</a>. 172800 IN NS <a href="http://ns4.google.com" target="_blank">ns4.google.com</a>.<br>
;; Received 168 bytes from 192.41.162.30#53(<a href="http://l.gtld-servers.net" target="_blank">l.gtld-servers.net</a>) in 296 ms</div>
<div><a href="http://www.google.com/" target="_blank">www.google.com</a>. 604800 IN CNAME <a href="http://www.l.google.com/" target="_blank">www.l.google.com</a>.<br><a href="http://l.google.com" target="_blank">l.google.com</a>. 86400 IN NS <a href="http://c.l.google.com" target="_blank">c.l.google.com</a>.<br>
<a href="http://l.google.com" target="_blank">l.google.com</a>. 86400 IN NS <a href="http://b.l.google.com" target="_blank">b.l.google.com</a>.<br><a href="http://l.google.com" target="_blank">l.google.com</a>. 86400 IN NS <a href="http://a.l.google.com" target="_blank">a.l.google.com</a>.<br>
<a href="http://l.google.com" target="_blank">l.google.com</a>. 86400 IN NS <a href="http://g.l.google.com" target="_blank">g.l.google.com</a>.<br><a href="http://l.google.com" target="_blank">l.google.com</a>. 86400 IN NS <a href="http://e.l.google.com" target="_blank">e.l.google.com</a>.<br>
<a href="http://l.google.com" target="_blank">l.google.com</a>. 86400 IN NS <a href="http://d.l.google.com" target="_blank">d.l.google.com</a>.<br><a href="http://l.google.com" target="_blank">l.google.com</a>. 86400 IN NS <a href="http://f.l.google.com" target="_blank">f.l.google.com</a>.<br>
;; Received 276 bytes from 216.239.34.10#53(<a href="http://ns2.google.com" target="_blank">ns2.google.com</a>) in 349 ms</div>
<div> </div>
<div>Here is result of querying ns record from <a href="http://ns1.google.com" target="_blank">ns1.google.com</a></div>
<div> </div>
<div> </div>
<div>> <a href="http://google.com" target="_blank">google.com</a><br>Server: [216.239.32.10]<br>Address: 216.239.32.10</div>
<div>------------<br>Got answer:<br> HEADER:<br> opcode = QUERY, id = 6, rcode = NOERROR<br> header flags: response, auth. answer, want recursion<br> questions = 1, answers = 4, authority records = 0, additional = 4</div>
<div> QUESTIONS:<br> <a href="http://google.com" target="_blank">google.com</a>, type = NS, class = IN<br> ANSWERS:<br> -> <a href="http://google.com" target="_blank">google.com</a><br> nameserver = <a href="http://ns2.google.com" target="_blank">ns2.google.com</a><br>
ttl = 345600 (4 days)<br> -> <a href="http://google.com" target="_blank">google.com</a><br> nameserver = <a href="http://ns3.google.com" target="_blank">ns3.google.com</a><br> ttl = 345600 (4 days)<br>
<font color="#cc0000"> </font><font color="#ff0000">-> <a href="http://google.com" target="_blank">google.com</a><br>
nameserver = <a href="http://ns1.google.com" target="_blank">ns1.google.com</a><br> ttl = 345600 (4 days)<br></font> -> <a href="http://google.com" target="_blank">google.com</a><br> nameserver = <a href="http://ns4.google.com" target="_blank">ns4.google.com</a><br>
ttl = 345600 (4 days)<br> ADDITIONAL RECORDS:<br> -> <a href="http://ns1.google.com" target="_blank">ns1.google.com</a><br> internet address = 216.239.32.10<br> ttl = 345600 (4 days)<br> -> <a href="http://ns2.google.com" target="_blank">ns2.google.com</a><br>
internet address = 216.239.34.10<br> ttl = 345600 (4 days)<br> -> <a href="http://ns3.google.com" target="_blank">ns3.google.com</a><br> internet address = 216.239.36.10<br> ttl = 345600 (4 days)<br>
-> <a href="http://ns4.google.com" target="_blank">ns4.google.com</a><br>
internet address = 216.239.38.10<br> ttl = 345600 (4 days)</div>
<div>------------<br><a href="http://google.com" target="_blank">google.com</a><br> nameserver = <a href="http://ns2.google.com" target="_blank">ns2.google.com</a><br> ttl = 345600 (4 days)<br><a href="http://google.com" target="_blank">google.com</a><br>
nameserver = <a href="http://ns3.google.com" target="_blank">ns3.google.com</a><br> ttl = 345600 (4 days)<br><a href="http://google.com" target="_blank">google.com</a><br> nameserver = <a href="http://ns1.google.com" target="_blank">ns1.google.com</a><br>
ttl = 345600 (4 days)<br><a href="http://google.com" target="_blank">google.com</a><br> nameserver = <a href="http://ns4.google.com" target="_blank">ns4.google.com</a><br> ttl = 345600 (4 days)<br><a href="http://ns1.google.com" target="_blank">ns1.google.com</a><br>
internet address = 216.239.32.10<br> ttl = 345600 (4 days)<br><a href="http://ns2.google.com" target="_blank">ns2.google.com</a><br> internet address = 216.239.34.10<br> ttl = 345600 (4 days)<br>
<a href="http://ns3.google.com" target="_blank">ns3.google.com</a><br>
internet address = 216.239.36.10<br> ttl = 345600 (4 days)<br><a href="http://ns4.google.com" target="_blank">ns4.google.com</a><br> internet address = 216.239.38.10<br> ttl = 345600 (4 days)<br>
></div>
<div> </div>
<div> </div>
<div>As shown above ,the first result from dig show that <a href="http://ns1.google.com" target="_blank">ns1.google.com</a> record in com. has ttl= <font color="#000000">172800 but the second result from querying one of <a href="http://google.com" target="_blank">google.com</a> zone authorize which in is case is <a href="http://ns1.google.com" target="_blank">ns1.google.com</a> show that ttl=345600.</font></div>
<div> </div>
<div>If one day <a href="http://google.com" target="_blank">google.com</a> remove <a href="http://ns1.google.com" target="_blank">ns1.google.com</a> from com. or any changing to <a href="http://ns1.google.com" target="_blank">ns1.google.com</a>. How fast do other domain 's caching dns know these changing? 172800 or 345600 ? </div>
<div> </div>
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