Re: [dnsext] [Technical Errata Reported] RFC2782 (2984)

[Marc Petit-Huguenin <[e-mail]>]

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The algorithm described in RFC 2782 is what it is, and people know how to
configure the values in an SRV RR to achieve what they want.  If some disagree
with this algorithm, they should work on a rfc2782bis document, but not try to
change the meaning of RFC 2782 in an errata.

On 10/04/2011 01:39 PM, RFC Errata System wrote:
>
> The following errata report has been submitted for RFC2782,
> "A DNS RR for specifying the location of services (DNS SRV)".
>
> --------------------------------------
> You may review the report below and at:
> http://www.rfc-editor.org/errata_search.php?rfc=2782&eid=2984
>
> --------------------------------------
> Type: Technical
> Reported by: Jordan Brown <[e-mail]>
>
> Section: Weight
>
> Original Text
> -------------
>         To select a target to be contacted next, arrange all SRV RRs
>         (that have not been ordered yet) in any order, except that all
>         those with weight 0 are placed at the beginning of the list.
>
>         Compute the sum of the weights of those RRs, and with each RR
>         associate the running sum in the selected order. Then choose a
>         uniform random number between 0 and the sum computed
>         (inclusive), and select the RR whose running sum value is the
>         first in the selected order which is greater than or equal to
>         the random number selected. The target host specified in the
>         selected SRV RR is the next one to be contacted by the client.
>         Remove this SRV RR from the set of the unordered SRV RRs and
>         apply the described algorithm to the unordered SRV RRs to select
>         the next target host.  Continue the ordering process until there
>         are no unordered SRV RRs.  This process is repeated for each
>         Priority.
>
> Corrected Text
> --------------
> Correcting the text requires agreement on what to do with entries with
> weight=0, so I don't want to try to craft text until we have agreement there.
>
> Notes
> -----
> The problem with this algorithm is that for a total weight T, it generates a random number 0..T and so allocates T+1 shares and gives the extra share to the first entry.  Thus with weights {1, 1}, the first entry is selected 2/3 of the time while the second entry is selected 1/3 of the time.
>
> I suspect that this is an attempt to do *something* with entries with weight=0, but yields unobvious results there:  for {0, 1, 1}, the three entries are each selected 1/3 of the time.
>
> I suggest:
>
> - Ordering weight=0 entries to the end.
> - Generating random numbers 0..(T-1).
> - Using a "greater" test rather than "greater or equal".
> - Selecting weight=0 entries in any order when all of the weight!=0 entries have been selected.
>
> Instructions:
> -------------
> This errata is currently posted as "Reported". If necessary, please
> use "Reply All" to discuss whether it should be verified or
> rejected. When a decision is reached, the verifying party (IESG)
> can log in to change the status and edit the report, if necessary.
>
> --------------------------------------
> RFC2782 (draft-ietf-dnsind-rfc2052bis-05)
> --------------------------------------
> Title               : A DNS RR for specifying the location of services (DNS SRV)
> Publication Date    : February 2000
> Author(s)           : A. Gulbrandsen, P. Vixie, L. Esibov
> Category            : PROPOSED STANDARD
> Source              : DNS Extensions
> Area                : Internet
> Stream              : IETF
> Verifying Party     : IESG
> _______________________________________________
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> https://www.ietf.org/mailman/listinfo/dnsext
>


- -- 
Marc Petit-Huguenin
Personal email: [e-mail]
Professional email: [e-mail]
Blog: http://blog.marc.petit-huguenin.org
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