unknown host

[abcd]

I have a linux machine (ip = 10.10.10.8), which can ping other
machines on the same subnet...such as

10.10.10.1
10.10.10.2
10.10.10.5
10.10.10.6
10.10.10.254

If I use socket.gethostbyaddr(<ip>) I get back results when ip is
10.10.10.1 and 10.10.10.254 but for the other IP addresses
(10.10.10.5, .6, etc) I get back "unknown host".  In fact I get
"unknown host" for the linux machine that I run the gethostbyaddr
from.

If perform the same operation from a windows machine (ip = 10.10.10.5)
it returns data for the other IP addresses as expected.

any ideas?