<html><head><meta http-equiv="Content-Type" content="text/html charset=GB2312"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div><blockquote type="cite"><div style="font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><blockquote type="cite"><a href="http://example.com">example.com</a>.<span class="Apple-tab-span" style="white-space: pre;"> </span>86400<span class="Apple-tab-span" style="white-space: pre;"> </span>NS<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre;"> </span><a href="http://a.example.net">a.example.net</a>.<br><a href="http://example.com">example.com</a>.<span class="Apple-tab-span" style="white-space: pre;"> </span>86400<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre;"> </span>NS<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre;"> </span><a href="http://b.example.net">b.example.net</a>.<br><a href="http://example.com">example.com</a>.<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre;"> </span>86400<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre;"> </span>NS<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre;"> </span><a href="http://c.example.net">c.example.net</a>.<br><br><a href="http://a.example.net">a.example.net</a>. 3600 A 1.1.1.1<br><a href="http://b.example.net">b.example.net</a>. 3600 A 2.2.2.2<br><a href="http://c.example.net">c.example.net</a>. 3600 A 3.3.3.3<br><br>and<br><br><a href="http://example.com">example.com</a>.<span class="Apple-tab-span" style="white-space: pre;"> </span>86400<span class="Apple-tab-span" style="white-space: pre;"> </span>NS<span class="Apple-converted-space"> </span><span class="Apple-tab-span" style="white-space: pre;"> </span><a href="http://a.example.net">a.example.net</a>.<br><br><a href="http://a.example.net">a.example.net</a>. 3600 A 1.1.1.1<br><a href="http://a.example.net">a.example.net</a>. 3600 A 2.2.2.2<br><a href="http://a.example.net">a.example.net</a>. 3600 A 3.3.3.3<br><br><br>Since all the name servers are in <a href="http://example.net">example.net</a> zone, these two configure both specify three name servers<br>for <a href="http://example.com">example.com</a> zone and will be affected if <a href="http://example.net">example.net</a> name server failed. And the latter configuration<span class="Apple-converted-space"> </span><br>will generate smaller package. But the first configuration seems more common, so what¡¯s the benefit?<br></blockquote><br>From what I understand, when 1.1.1.1 fails to respond, all of<br><a href="http://a.example.net/">a.example.net</a><span class="Apple-converted-space"> </span>will be considered bad, so 2.2.2.2 and 3.3.3.3 won't be<br>queried at all, and a resolver will return a SERVFAIL.</div></blockquote><br><div>AFAIK, Recursive name server has name server cache which store several entries, each of them includes</div><div>zone name</div><div>ip address</div><div>other information including RTT, EDNS version, etc</div><div>So after the recursive name server get the NS records and related glue, both of the configuration should generate</div><div>similar name server entities, and only if all of them failed to answer the query, the recursive server will return SERVFAIL</div><div>to resolver. </div><div><br></div><blockquote type="cite"><div style="font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;"><br>--<span class="Apple-converted-space"> </span><br>Dave Warren<br><a href="http://www.hireahit.com/">http://www.hireahit.com/</a><br><a href="http://ca.linkedin.com/in/davejwarren">http://ca.linkedin.com/in/davejwarren</a><br><br><br>_______________________________________________<br>dns-operations mailing list<br><a href="mailto:dns-operations@lists.dns-oarc.net">dns-operations@lists.dns-oarc.net</a><br><a href="https://lists.dns-oarc.net/mailman/listinfo/dns-operations">https://lists.dns-oarc.net/mailman/listinfo/dns-operations</a><br>dns-jobs mailing list<br><a href="https://lists.dns-oarc.net/mailman/listinfo/dns-jobs">https://lists.dns-oarc.net/mailman/listinfo/dns-jobs</a></div></blockquote></div><br></body></html>