[dnsop] DNS Anycast revisited (fwd)

Wed May 4 02:28:52 UTC 2005

Dean Anderson wrote:
> 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. 
> 
Context helps.

In the previous paragraph Vixie said:

> while i'm on the subject, i also remain convinced that using anycast to do
> distributed load balancing for applications like WWW, on the assumption
> that the path you heard a dns query on is instructive as to what content
> would be best to answer with, is silly, and will more often do harm or do
> nothing than do good.  (and i've told akamai and speedera this many times.)
> ("but it makes for great marketing slideware.")
> 

In other words this is a bad idea:

[FT at fenrir FT]$ dig a248.e.akamai.net @69.45.79.10

;; ANSWER SECTION:
a248.e.akamai.net.      20      IN      A       80.67.72.214
a248.e.akamai.net.      20      IN      A       80.67.72.201

FT at inuyasha:~$ dig a248.e.akamai.net @69.45.79.10

;; ANSWER SECTION:
a248.e.akamai.net.      20      IN      A       69.45.79.15
a248.e.akamai.net.      20      IN      A       69.45.79.16

While I'm not a mind reader, It seems he's saying that, since Ultradns 
doesn't use anycast to do this, it is an example of 'good anycast.'