can't verify hostname: getaddrinfo...

[David Tonhofer]

Ryan Golhar wrote:
> 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
>   
On a hunch, this seems to be a DNS problem, I don't know whether this is 
correct but does
the lookup "IP address" -> "reverse address" -> "IP address" seems to 
fail, probably because
the ISP has a messily configured DNS?

1) Try this on the command line (the 'rdig.pl' program is just a reverse 
lookup perl program that uses 'dig',
see the attached program; use that or just execute 'dig 
1.2.3.4.in-addr.arpa. PTR' instead of 'rdig.pl 4.3.2.1'

"rdig.pl 1.1.1.1" should give "host-1-1-1-1.abc.net" - if not, your 
setup won't work

"dig host-1-1-1-1.abc.net" should give "1.1.1.1" - if not, your setup 
SHOULD not work

2) See "man getaddrinfo"

Best regards,

 -- David


----------8<-----------------rdig--------------------

#!/usr/bin/perl -w

if (!defined $ARGV[0]) {
  print STDERR "You have to pass an IP address to reverse-resolve\n";
  exit 1;
}

if ($ARGV[0] =~ /^(\d+)\.(\d+)\.(\d+)\.(\d+)$/) {
  $reverse="$4.$3.$2.$1.in-addr.arpa";
  open(PIPE,"/usr/bin/dig $reverse PTR|") or die "Could not open pipe: 
$!\n";
  @lines = <PIPE>;
  close(PIPE) or die "Could not close pipe: $!\n";
  foreach $line (@lines) {
    print $line;
  }
  exit 0;
}
else {
  print STDERR "The passed argument $ARGV[0] is not an IP address\n";
  exit 1;
}