[isp-dns] CNAME vs A record load-balancing? (and akadns.net)

["Jonathan B." <jlb0001@...>]

It seems like many major sites have their DNS hosted by Akamai.com.  For 
example, yahoo.com, google.com, cbs.com, nba.com all have a similar setup:

 ;; QUESTION SECTION:
 ;www.google.com.                        IN      A

 ;; ANSWER SECTION:
 www.google.com.         3600    IN      CNAME   www.google.akadns.net.
 www.google.akadns.net.  300     IN      A       216.239.41.99

In these setups, generally they map the domain record in question to a CNAME 
in the akadns.net domain.  So my question is why use a CNAME? Why not just 
have the name servers set to ns1.akadns.net so that only one hit to remote 
DNS servers are required to resolve the A record(s)?  (With this setup, it 
appears to me to take at least 2 separate DNS requests to resolve the name.) 
 So, why not just have multiple A records setup for round-robin DNS-based 
load balancing (so only one request has to be made)?

One other interesting nuance I saw is the difference between yahoo.com and 
nba.com.  In nba.com's setup, the answers come back in only one hit to their 
name server, as if cached by a non-authoritative name server.  If CNAMEs are 
the way to go (for a reason I hope someone will explain), why not specify a 
"non-authoritative" name server as the "authoritative" name server in all 
cases (so the CNAME is resolved without penalty of another hit)?  
(Admitidly, my use of "authoritative" is surely imprecise; so I beg that you 
try to infer what I mean by taking a look at these two different domains via 
dig to the authoritative name servers of each.)  Of course, if this method 
of a caching, front-end DNS server is acceptable, then, again, why not just 
use the older-fashioned A record round-robin method?

SEE:
dig @ns1.yahoo.com www.yahoo.com
dig @NS10.NBA-HQ.COM www.nba.com

Thanks for your comments!

-Jonathan

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