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@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@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.'