Re: host & DNS

[Peter Billson <pete@elbnet.com>]

> I am trying to understand how the hosts.allow and hosts.deny files work as
> well as DNS.
> 
> So far, I have a nameserver, but kept getting an error:
> 
> warning: /etc/hosts.allow, line 11: can't verify hostname:  gethostbyname
> (gomez.star.cd) failed
> 
> I finally figured out that something was wrong as one of this ISP's user
> complained that they couldn't send an email to my mailserver (which is the
> nameserver as well).
> 
> I did a host lookup and got the following:
> 
> host 203.36.43.17
> Name: gomez.star.cd
> Address: 203.36.43.17
> 
> then later:
> 
> host gomez.star.cd
> gomez.star.cd does not exist, try again


It sounds like you have two problems.

DNS shouldn't be affected by the hosts.allow/deny files since it is not
run out of inet.d and the "can't verify hostname" indicates that you
have a DNS problem.
Check the daemon log to see if bind is complaining. Does it stay running
after you start it? Do you have reverse DNS working properly?

Second, you really can't filter connections to your mail server if you
are running a public mailserver, since you want everyone in the world to
be able to send you mail. Of course you could try to filter out spammers
that way, but that would be like playing wack-a-mole.

There is a lot of reference material. Check out
http://www.google.com/search?hl=en&q=linux+tcpwrappers

Pete
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