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Some clients use SRV lookups, a few (to their embarrassment) do not (2009)

101 点作者 dedalus将近 7 年前

12 条评论

inopinatus将近 7 年前
There already is a SRV service name reservation for both http and www-http, with Tim Berners-Lee as the contact name. Fun fact: using DNS address records (&quot;A&quot; or &quot;AAAA&quot;) for endpoint name resolution in HTTP is a convention; it is not required in the standard or in any of the normative references. Web services do not own the address record and should never have been using it in the first place. Nonetheless they continue squatting addresses in a de facto assertion of unwarranted privilege, and every other use of the DNS has to steer carefully around.<p>When SRV is discussed e.g. on the HTTP&#x2F;2 list, the objections of resolution speed and number of round-trips are usually raised. But SRV records do not intrinsically require an additional lookup or round trip. Unoptimised zone configurations (especially those that slice at _tcp, which occurs at some Microsoft shops) may fare less well, but that is true of all DNS configuration. Services that care about resolution speed already optimise their DNS as necessary, and they would for SRV as well if it were mandated.<p>In practice, the reasons for non-adoption are, mundanely, simply a matter of inertia, combined with a lack of motivation: the browser vendors who in practice write the HTTP standard do not care to change and have no external force that will push them off overloading the address record.
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andrewstuart2将近 7 年前
There&#x27;s a couple things about modern DNS that just doesn&#x27;t make sense. There&#x27;s probably a good explanation buried somewhere in a mailing list or three.<p>The other one that still astounds me is that DV certificates rely entirely on DNS control for validation prior to issuance, and browsers trust that system, but there still exists no way for me to cut out the middle man and put my own domain-specific CA Cert in DNS directly.
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exabrial将近 7 年前
Having service location be at the TCP&#x2F;IP level is a major contributor to the IPV4 crisis. We have 48 bit addresses, but 16 of those bIts are relatively unused.<p>Rather than solving the problem the pragmatically (and in a backwards compatible way), we&#x27;re pushing a reinvention of the wheel (protocol).<p>IPv4 certainly has problems but I think they were solvable without bisecting the internet.
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mehrdadn将近 7 年前
Remote Desktop really needed to use SRV. It&#x27;s just so much more convenient to be able to connect to foo.example.com and have that bind to example.com:12345 when all you have is 1 IP address.
JdeBP将近 7 年前
For what it is worth, that is not actually my title, and the answer does deal with a lot of things <i>other</i> than that subject including the many things that one can discover <i>do</i> use SRV resource record sets.<p>Enjoy a related discussion of some poor FTP clients:<p>* <a href="http:&#x2F;&#x2F;jdebp.info.&#x2F;FGA&#x2F;web-browser-ftp-hall-of-shame.html" rel="nofollow">http:&#x2F;&#x2F;jdebp.info.&#x2F;FGA&#x2F;web-browser-ftp-hall-of-shame.html</a>
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ben0x539将近 7 年前
Just from the article and some of the comments here, it&#x27;s not quite clear to me what the motivation for making HTTP use SRV records is. To me, naively, it seems like relying on A&#x2F;AAAA records a) &quot;works&quot;, and b) is central to a lot of people&#x27;s intuition of how networking services function.<p>Following some of the links in the article, I&#x27;ve seen people make arguments on how straightforward it would be to implement and how it clearly works well for some non-HTTP systems. I&#x27;m guessing there&#x27;s some implicit shared understanding of the problem space that I, as an uninitiated, casual DNS user, can&#x27;t really wrap my head around.<p>Can y&#x27;all point me in the right direction to read something about, like, what problems SRV records solve for HTTP, and specifically how that solution compares to how people have traditionally solved those problems with HTTP? There seems to be some tension between best practices as established by IETF RFCs and best practices coming from decades of deploying public-facing HTTP infrastructure&#x2F;browsers, does that sound about right?
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fuzzy2将近 7 年前
Hm. Sounds great and all, but there’s a catch: All “managed” networks (corporate, schools or otherwise) are built on the fact that port 80 means HTTP and port 443 means HTTPS.<p>I don’t see SRV in use for browsers, ever.
a1r将近 7 年前
Fun fact: the Minecraft client has for years supported SRV to discover the server port number. Thanks Notch.
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amaccuish将近 7 年前
It would be great if you could do a DNS lookup, and in the request, say I want x record types for y name. Like, give me A, AAAAA, CNAME and SRV records for apple.com. I guess there&#x27;s opportunity for abuse, but I think it would be better than ANY.
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Qwertie将近 7 年前
SRV lookups for http would have been great as some ISPs block well known ports.
nickodell将近 7 年前
I think this page needs more explanation of the motivation behind this request. Why should browser vendors give a shit?<p>Yeah, it&#x27;s a standard, and at least three people want to use it, but what else?
j16sdiz将近 7 年前
I am not sure to whom embrassment this is.<p>I prefer my http server fast, works over firewall and less depends on other services.
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