Subject: [NSIS] Retransmitted Queries

From: Roland Bless <[email-masked]>
Date: Fri, 24 Nov 2006 17:20:45 +0100

Hi Robert and all,

In section 5.3.3. there is the statement:

  Retransmitted Queries MUST use different Query-Cookie values.

Is there any rationale for this (yes, I read sec. 8.5)?
I cannot see any real benefit in doing
so (except for the case that you want to measure round-trip times).
Replay attacks seem to cause no harm, because they do not
cause additional state to be installed. In the current situation,
we have often seen the case where retransmissions and responses
are crossing each other (or two queries are transmitted back-to-back)
and the responder has to send one response for each query until the
backoff is large enough to allow a query cookie match for the latest
query/response pair. If we require that every Query must be answered
by a Response (in order to recover from lost Responses) I see an
advantage of using the same query cookie for retransmissions:
The context will be established earlier, as soon as
the first response hits the querier, so the latter will stop the
retransmission of queries. Subsequent responses can be dropped
because state was already established at the querier.
I guess that I overlooked something...

Regards,
 Roland

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