BIND caching servers like slower Auth servers ?

I’ve found an interesting document about BIND recursive servers.

--
Authority Server Selection of DNS Caching Resolvers
http://irl.cs.ucla.edu/data/files/papers/res_ns_selection.pdf
--

Seen from this document , BIND Caching Name Servers seem to like slower Authoritative Name servers.

I checked this behavior with BIND and unbound.
Here’s the result I did.

[ recursive server info ]

I installed bind and unbound with apt-get.

# lsb_release –a No LSB modules are available. Distributor ID: Ubuntu Description:    Ubuntu 12.04.1 LTS Release:        12.04 Codename:       precise # uname -ri 3.5.0-030500-generic x86_64 # rndc status | head -1 version: 9.8.1-P1 # unbound-control status | head -1 version: 1.4.16

[ conditions ]

I have prepared four auth servers.
queryperf sent unique 3,000 DNS queries to the recursive sever and I counted # of DNS queries which is sent to the Auth servers from BIND/unbound caching name server.

queryperf -- recursive server -- ns1.foobar.com ( no delay )                           -- ns2.foobar.com ( delay 50msec )                           -- ns3.foobar.com ( delay 500 msec )                           -- ns4.foobar.com ( delay 1000 msec )

[ results ]

# of queries sent to Auth servers from BIND or unbound

	ns1.foobar.com no delay	ns2.foobar.com delay 50msec	ns3.foobar.com delay 500msec	ns4.foobar.com delay 1000msec
BIND 9.8.1-P1	2472	130	425	603
Unbound 1.4.16	1480	1509	46	43

In my testing result , BIND seems to like slower Auth servers..
total # of queries BIND/unbound sent to the Auth servers is more than 3,000 queries.
I guess this was caused by retransmission DNS queries.

Please note that this result might differ from the testing conditions.