[ale] Sendmail latency

[Jim Popovitch]

On Tue, 2005-01-25 at 00:59 -0500, Ryan Fish wrote:
>  - The mail server is the only one experiencing the following issue with the
>  'host' cmd:
> 
>  [root at mailserver mail]# host app01
>  app01.clientdomain.com has address 192.168.3.0
>  [root at mailserver mail]# host app02
>  app02.clientdomain.com has address 192.168.3.0
>  [root at mailserver mail]# host app101
>  app101.clientdomain.com has address 192.168.3.220 (correct)
>  [root at mailserver mail]# host app102
>  app102.clientdomain.com has address 192.168.3.0
>  [root at mailserver mail]# host mailserver
>  mailserver.clientdomain has address XX.XXX.XXX.199 (the correct IP address)
> 

Based on the above data, you need to check the DNS server(s) specified
in /etc/resolv.conf and determine why they are resolving app01 and app02
as 192.168.3.0.  Secondly, you need to test the following:
 
  # host 192.168.3.220 
  # host XX.XXX.XXX.199 

Verify that the above reports the correct reverse lookup for those IP
addresses.

>  - I changed the domain names to protect the innocent...  The domains in
>  question are valid though.

Yes, but you left one valid IP address in there. ;-)


> - How would I setup a caching name server on the mail server?  named is
>  running on that box and named.conf contains info for each domain hosted by
>  the client however there I can find no other DNS info (as far domains not
>  hosted by the client) on this box but I have no idea where to look for
> that.

RHEL has a package called caching-nameserver, install it and you should
be good.  FIRST backup your existing /etc/named.conf as well
as /var/named/*.  Caching-nameserver will add a few entires
to /etc/named.conf as well as a file or two to /var/named.

I would also encourage you to look at running named inside a chroot'ed
environment.  However that is a discussion for another day.  When you
are curious just google for "chroot named".

Assuming you have rndc all setup in /etc/named.conf, once you have
things running issue this command: "rndc querylog" and then tail
-f /var/log/messages to see how fast or slow DNS queries are being
resolved.  Don't leave querylog enabled on a busy box. ;-)

-Jim P.