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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Harshith,<o:p></o:p></span></p>
<p class="MsoNormal" style="text-indent:.5in"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">I think you need to understand the proportionality here: the *<b>vast*majority</b>* of the time, the client already knows the port (because
ports tend to be pre-assigned for specific services), and only needs to resolve the FQDN to one or more address records (A and/or AAAA records), in order to make a connection. This isn’t really a burden, or complicated logic in the client software, since it
can just call a generic hostname lookup function (e.g. the traditional gethostbyname() or the more modern getaddrinfo()). It’s not like every application programmer needs to deal with parsing packet contents, handling retries, dealing with label compression,
etc. This is all handled in the library routine.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Only in a small minority of cases do clients go through the whole NAPTR or SRV process. Some of the main scenarios for that include:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:black"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Microsoft Active Directory. The clients use SRV records as part of the so-called “dc locator” process to find a domain controller that provides a specific
service<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:black"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Certain IM clients (like Lync) use SRV records to find SIP services<o:p></o:p></span></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><![if !supportLists]><span style="font-size:11.0pt;font-family:Symbol;color:black"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">SIP telephony clients use NAPTR records<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">Note that SMTP clients use MX records rather than SRV records. MX records can be considered the simpler, mail-specific precursor to SRV records. Theoretically,
SMTP _<i>could</i>_ be switched over to use SRV records, but the use of MX is so ingrained that it’s probably not worth the (massive) effort.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">If you look at nameserver query statistics, you’ll see that the volume of SRV and/or NAPTR queries on a typical nameserver/resolver is a miniscule fraction of
the A/AAAA traffic. Where MX-record traffic falls between those extremes, will depend a lot on whether the nameserver/resolver is internal or external, whether the particular domain is heavily used for mail, etc.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:black">
- Kevin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> bind-users-bounces@lists.isc.org [mailto:bind-users-bounces@lists.isc.org]
<b>On Behalf Of </b>Chris Buxton<br>
<b>Sent:</b> Tuesday, October 13, 2015 7:58 AM<br>
<b>To:</b> Harshith Mulky<br>
<b>Cc:</b> BIND Users<br>
<b>Subject:</b> Re: SRV Request to DNS<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">On Oct 5, 2015, at 11:51 PM, Harshith Mulky <<a href="mailto:harshith.mulky@outlook.com">harshith.mulky@outlook.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">Let us say we are having a FQDN and we need to Resolve it. It goes through the procedure of determining the IP and Port using NAPTR/SRV/A query mechanisms<o:p></o:p></p>
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<p class="MsoNormal"><br>
The question I have is if I have a FQDN with a Port Number already determined, will it go through the Procedure of NAPTR/SRV/A query (or) simply do a A query (or) Is this left to the client to apply the Logic?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">The client must supply the logic. DNS is conceptually a simple database service — ask a question, get an answer. The logic of using NAPTR records, SRV records, A records, AAAA records, and CNAME records is mostly handled by the client.
(CNAME and DNAME records are the primary exception, triggering extra processing on the recursive name server.)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Chris<o:p></o:p></p>
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