[dnsop] DNS Anycast revisited (fwd)

Wed May 4 01:50:50 UTC 2005

On Tue, 3 May 2005, Paul G wrote:

> i'm terribly sorry, but i'm unable to extract any meaning at all from these
> statements. when i parse them, they make no sense at all (not in terms of
> being wrong, just not understandable). could you rephrase them?
> 
> coherency and consistency are well-defined terms in systems engineering. we
> are talking about dns queries and hence coherency of zone data (the shared
> resource). i fail to see how this is open to any interpretation at all.

Sorry, The original statement Vixie made is nonsense. Here is the original
statement again:

Vixe writes:
   lest anyone be confused, ultradns's anycast for .ORG is completely
   coherent and doesn't admit the possibility of giving out different
   responses from different anycast nodes for policy reasons or any other
   reason, and so it's an example of "good" anycast the way i count such
   things.

Vixie seems to be responding to concern raised for Ultradns' pervasive use
of anycasting. This was the only issue raised involving Ultradns.

During the anycast discussion on DNSOP, the subject of zone coherency (as
normally used) was not an issue.  So there is no question of zone
coherency for Ultradns' servers. We assumed (and did not dispute) that
zone updates were unaffected by anycast. Zone updates happen over private
secure channels on non-anycasted IP addreses. They ought to be as coherent
as DNS gets. They ought not be affected by anycast.

Vixie ends by saying essentially, that because of Ultradns' coherency, it
is an example of "good anycast". But the two issues (coherency and
anycast) have no relationship. There is no reason to conclude that
coherency means anycast is either good or bad. Hence, his statement is
nonsense. 

Alternately, one might read "coherency" as refering to the shared TCP
state of the group of servers. The "shared TCP state" of a group of
anycast servers is conceptual.  There is no actual coherency for this
shared TCP state. So that is nonsense, too.

I suspect the statement is just nonsense, that is hoped to sound good.  
Many people will not really read or parse his whole statement, but will
remember 'Ultradns is an example of good anycast, according to Vixie'

But, given that the original statement is nonsense, I can't really say
that any of these are correct.

		--Dean

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