Subject: LLMNR Issue 45: Handling of Unqualified Names

From: Bernard Aboba <[email-masked]>
Date: Thu, 4 Sep 2003 21:52:59 -0700 (PDT)

Issue 45: Handling of Unqualified Names
Submitter name: Stuart Cheshire
Submitter email address: [email-masked]
Date first submitted: August 24, 2003
Reference:
Document: LLMNR-22
Comment type: T
Priority: S
Section: Various
Rationale/Explanation of issue:

>Today, with the rise of home networking, there are an increasing number
>of ad-hoc networks operating without a Domain Name System (DNS) server.

I think this is side-stepping the real issue. The real issue is:

>Today, with the rise of home networking, there are an increasing number
>of home users who do not have ownership of any part of the name space
>in which they can assign names.

The whole section talking about "unqualified names" seems to be skirting
around this issue without being willing to face it head-on and tackle it.
Section 3.1 says:
>3.1. Unqualified names
>
>The same host MAY use LLMNR queries for the resolution of unqualified
>host names, and conventional DNS queries for resolution of other DNS
>names.
>
>If a name is not qualified and does not end in a trailing dot, for the
>purposes of LLMNR, the implicit search order is as follows:
>
>[1] Request the name with the current domain appended.
>[2] Request just the name.

You can't "request just the name". There is no way to represent an
unqualified name ("no trailing dot") in the DNS packet format. What you
mean is:

>[1] Request the name with the current domain appended.
>[2] Request the name with the root domain (".") appended.

What this means is that if a home user calls their TV "tv", and their FM
radio receiver "fm", and their CD player "cd", their computer is going to
be sending queries for the TLDs "tv.", "fm." and "cd." (Tuvalu, Federal
State of Micronesia, and Democratic Republic of the Congo, respectively.)

This seems like it invites chaotic uncontrolled pollution of the
top-level name space.

[BA] I assume you are referring to DNS queries for "tv." Presumably there
is no harm in allowing LLMNR queries for this. The draft allows a host to
resolve queries for unqualified names only via LLMNR, so this can be
avoided. Are you suggesting that this behavior be recommended?

Furthermore, because there is no way to represent an unqualified name in
the DNS packet format, there is also no way to represent an unqualified
name on the right-hand-side of a PTR, CNAME or SRV record. This means
that if you do a LLMNR query for an SRV record with an "unqualified"
name, what you get back is an SRV record containing a target host name
that you can't use with LLMNR because it's not an "unqualified" name.

[BA] Agreed. This should be fixed.

>3.1. Unqualified names
>
>The same host MAY use LLMNR queries for the resolution of unqualified
>host names

Who makes the choice offered by that "MAY"? User? OS vendor? Application
writer?

[BA] The LLMNR implementation.

>If a name is not qualified and does not end in a trailing dot,

What does that mean? Do "fully qualified" and "ends in a trailing dot"
mean the same thing, or is there a difference?

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