LLMNR Issue 55: Sender Checks

[Bernard Aboba <aboba@internaut.com>]

LLMNR Issue 55: Sender checks
Submitter name: Bernard Aboba
Submitter email address: aboba@internaut.com
Date first submitted: December 3, 2003
Reference:
Document: LLMNR-25
Comment type: T
Priority: S
Section: 2-2.8
Rationale/Explanation of issue:

Section 2 states:

[4] Upon the reception of the response, the sender performs the checks
described in Section 2.5. If these conditions are met, then the
sender uses and caches the returned response. If not, then the
sender ignores the response and continues waiting for the response.

It is not clear what sender checks this paragraph is referring to.
Possibilities include material in sections 2.3, 2.5, 2.8 and 3.1.

Section 2.3 does include some sender checks. For example:

"If the sender of a TCP query receives a response not
using TCP, the response MUST be silently discarded." There is also
discussion of handling of ICMP "time exceeded" messages.

Section 2.5 does not specify checks to be made by senders on reception of
a response. For example, there are recommendations on setting of TTL/hop
count by senders, but no TTL check specified for receivers. Since the
sender MUST set the TTL/Hop Count field to 1, it is not possible for a
receiver to see a TTL/Hop Count field of 2 or larger. Yet no sender action
is specified upon reception of such a packet.

Within Section 2.5, the following paragraph is present:

"A sender SHOULD prefer RRs including reachable addresses where RRs
involving both reachable and unreachable addresses are returned in
response to a query."

I do not believe that this sentence implies a reachability test be done on
received RRs.

Section 2.8 provides guidelines for sender processing of the authority and
additional section of responses.

Section 3.1 talks about responder responsibilities, but not sender checks.
It includes the sentence:

"Routable addresses MUST be included first in the response, if available.
This encourages use of routable address(es) for establishment of new
connections."

[Ralph Droms] Section 2.5, third paragraph: what is an "unreachable
address"; did you intend "unroutable address"?

[BA] Proposed fixes:

In Section 2, change:

"[4] Upon the reception of the response, the sender performs the checks
described in Section 2.5. If these conditions are met, then the
sender uses and caches the returned response. If not, then the
sender ignores the response and continues waiting for the response."

to:

"[4] Upon reception of the response, the sender processes it."

In Section 2.5, delete:

"A sender SHOULD prefer RRs including reachable addresses where RRs
involving both reachable and unreachable addresses are returned in
response to a query."

In Section 2.1, add:

"Since the responder may order the RRs in the response so as to
indicate preference, the sender SHOULD preserve ordering
in the response to the querying application."

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