<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 14 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
pre
{mso-style-priority:99;
mso-style-link:"HTML Preformatted Char";
margin:0in;
margin-bottom:.0001pt;
font-size:10.0pt;
font-family:"Courier New";}
p.MsoAcetate, li.MsoAcetate, div.MsoAcetate
{mso-style-priority:99;
mso-style-link:"Balloon Text Char";
margin:0in;
margin-bottom:.0001pt;
font-size:8.0pt;
font-family:"Tahoma","sans-serif";}
span.HTMLPreformattedChar
{mso-style-name:"HTML Preformatted Char";
mso-style-priority:99;
mso-style-link:"HTML Preformatted";
font-family:"Courier New";}
span.EmailStyle19
{mso-style-type:personal;
font-family:"Calibri","sans-serif";
color:windowtext;}
span.EmailStyle20
{mso-style-type:personal-reply;
color:black;}
span.BalloonTextChar
{mso-style-name:"Balloon Text Char";
mso-style-priority:99;
mso-style-link:"Balloon Text";
font-family:"Tahoma","sans-serif";}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="#0563C1" vlink="#954F72">
<div class="WordSection1">
<p class="MsoNormal"><span style="color:black">In the grand tradition of _<i>ceci</i>_n’est_pas_une_pipe_, how dig *<b>represents</b>* a piece of TXT contents isn’t necessarily how it *<b>is</b>*.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">I just verified (via tcpdump) that a TXT record label that shows up as “blah\\” in dig’s (and host’s) output, actually only contains a single backslash (hex code 5C), on the wire. So, anything that uses a resolver-library
routine to fetch this data, will only see a single backslash. If it’s just a wrapper around “dig” or some other command-line utility, then it needs to know the idiosyncracies of whatever it’s wrapping.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">The reason that dig “over-escapes” stuff like this, in its representation, is so that folks can take dig output and paste it back into master files _<i>verbatim</i>_.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">I’d be more concerned about the folks asking for this TXT record. Seems they’re doing something proprietary, but not “sub-classing” their use with, say, an application-specific prefix, and, say, a colon delimiter.
If the “foo” app wanted a “path=” variable in a TXT record, maybe it could be encoded as “foo:path=xxx”, so that it would never collide with the “bar” app that later wants to also encode a “path=” variable, at the same point in the namespace hierarchy, for
a different, incompatible purpose.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black">This is part of the inherent problem with using DNS TXT records to store arbitrary app data. But, you most likely already know this, since the Experimental RFC you referenced (1464) discussed it briefly in Section
4.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black"> - Kevin<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:black"><o:p> </o:p></span></p>
<div>
<div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in">
<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 [mailto:bind-users-bounces@lists.isc.org]
<b>On Behalf Of </b>MURTARI, JOHN<br>
<b>Sent:</b> Tuesday, May 30, 2017 3:04 PM<br>
<b>To:</b> bind-users@lists.isc.org<br>
<b>Subject:</b> Ending a TXT record with a backslash?<o:p></o:p></span></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Folks,<o:p></o:p></p>
<p class="MsoNormal"> Recently had an issue with someone who wanted this for a TXT record:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">murt2 IN TXT "path=\";<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Now, not sure wny they wanted it – maybe the root directory in Windows??? But anyway, BIND does not like it.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">zone example.com/IN: loading from master file db.example.com failed: unbalanced quotes<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Of course, we could escape the backslash. Which BIND then likes and the zone will load. But a dig gives you:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">;; ANSWER SECTION:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New"">murt2.example.com. 83000 IN TXT "path=\\"<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Which isn’t really the same thing? Took a look at RFC1464 (Using DNS to Store Arbitrary String Attributes), <a href="https://tools.ietf.org/html/rfc1464">https://tools.ietf.org/html/rfc1464</a>, read this:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> All printable ASCII characters are permitted in the attribute value.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> No characters need to be quoted with a "`". In other words, the<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> first unquoted equals sign in the TXT record is the name/value<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> delimiter. All subsequent characters are part of the value.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> Once again, note that in most implementations the backslash character<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> is an active quoting character (and must, itself, be quoted).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""><o:p> </o:p></span></p>
<p class="MsoNormal"> That last sentence really has me stuck! Too many adjectives? Are there ‘inactive’ quoting characters?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The RFC did have an example, but I couldn’t work it out...<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> Attribute Attribute Internal Form External Form<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> Name Value (server to resolver) (TXT record)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New""> = \= `==\= "`==\\="<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"> Any suggestions are welcome & please excuse my attempts at humor above.<o:p></o:p></p>
<p class="MsoNormal"> Best regards!<o:p></o:p></p>
<p class="MsoNormal">John<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">---------------- <br>
John Murtari – <a href="mailto:jm5903@att.com">jm5903@att.com</a><o:p></o:p></p>
<p class="MsoNormal">Ciberspring<o:p></o:p></p>
<p class="MsoNormal">office: 315-944-0998<o:p></o:p></p>
<p class="MsoNormal">cell: 315-430-2702<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</body>
</html>