spf-discuss
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DNS Loading Comparison

2005-04-12 19:36:02
It looks like SPF has the potential of being 1000X more efficient than CSV in both number of DNS queries and cache sizes. I tried to bring this up on the CSV mailing list, but they don't want to hear it. So I bring it up here, in hopes of getting some check on my assumptions.

Assume:
      2,000 zombies, widely distributed
     50,000 emails from each zombie
100,000,000 recipient addresses, widely distributed
    100,000 recipient domains
          3 hops from sender to receiver
Then:
  2000 senders --> 3 hops -->  100,000 receivers
     approx. 150,000 MTAs needing to authenticate

Scenario E1:  All DNS queries to rr.com
    Total 150,000 queries, cached for 48 hours

Scenario E2:  DNS queries to 1000 servers, widely distributed
   Typical server:  serv138.austin.rr.com
   150,000 MTAs x 1000 servers = 150,000,000 queries !!
   Client caches are 1000X larger, and 1000X less
     likely to hit.

The CSV folks will insist on discussing the *worst case* for SPF, and that looks like maybe 100X more queries than CSV, but even with all those queries, the result is typically a few records for a sizable domain, so caching should still be effective.

If I'm right, we really need a way to *strongly encourage* efficient SPF records, while still allowing chained queries, if necessary.

--
Dave
************************************************************     *
* David MacQuigg, PhD      email:  dmquigg-spf at yahoo.com      *  *
* IC Design Engineer            phone:  USA 520-721-4583      *  *  *
* Analog Design Methodologies                                 *  *  *
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* VRS Consulting, P.C.              Tucson, Arizona 85710        *
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