can't verify hostname: getaddrinfo...

[Ryan Golhar]

I have a group of machines that are only accessible by users from
certain ISPs.  One of those ISPs, we'll call abc.net.  The example IP
address I will use is 1.1.1.1

In my /etc/hosts.allow, I have:

sshd: LOCAL, .abc.net

This was working for some time, but somewhere along the last few weeks
or months stopped working, and I don't know why.  

/var/log/secure reports the following:

sshd[7693]: warning: /etc/hosts.allow, line 10: can't verify hostname:
getaddrinfo(host-1-1-1-1.abc.net, AF_INET) failed 

sshd[7693]: refused connect from 1.1.1.1 (1.1.1.1)

The users are real and were able to get access to these machines.  I've
verified that I can get access to the machines from a different ISP, in
fact, most of the users can.  It just seems to be this 1 provider that
these 2 users have.  Any ideas where I can start looking to find the
cause of this problem?

Ryan