Subject: Re: Split DNS.

From: "Naresh Narang" <[email-masked]>
Date: Thu, 20 Jan 2000 14:50:14 IST

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Sir,

    The MX record on firewall points to Internal box. I thought it this way 
because in case if it is pointing to firewall itself sendmail will try to 
deliver it locally and will not be able to find the destination. So, MX 
record I put it for the Internal mail server. Yes I have put the address of 
both: the firewall box and Internal box in the resolv.conf. The internal DNS 
is having "forwarders" and it is working correctly.

     If I understand correctly, I think you are suggesting that in the 
firewall host I should put the MX record for the firewall itself and in the 
resolv.conf, the address of my Internal box. I'll try this. Please correct 
me if I am wrong.

    I tried Mailertable feature but it did not work. In the sendmail.cf I 
tried this:

Kmailertable hash /etc/mailertable.db

It was giving some error in dbm format of mailertable, so I used hash.  and 
yes I put the following in the mailertable entries:

.foo.com           smtp:your.internal.mail.host
foo.com           smtp:your.internal.mail.host

Regards,
N.K. Narang

----Original Message Follows----

Naresh:

The problem is that the MX record points to the firewall to deliver all
messages to for the domain *.foo.com. For the outside world, this is
correct. For your firewall, you must provide *some* mechanism to
instruct
sendmail to override the DNS settings.

My favoriate answer is to use the mailertable feature in the
sendmail.cf.
This file can contain an explicit selection of mailer and destination
for
any domain or host combination. In particular:

.foo.com           smtp:your.internal.mail.host

Will cause sendmail to route *any* traffic for the domain "foo.co"m to
"our.internal.mail.host" via the smtp mailer.

(I'm doing this from memory - check sendmail's cf/README documentation
to verify
  the format.)

==========
An alternative would be to use the following "slight of hand" with the
DNS:

         (0) The external DNS should have an MX record pointing to your
firewall.
              I *think* you already have this.

	(1) Put a MX record on the internal DNS which points to your internal
             email server.

	(2) Add a "forward" statement to make the internal DNS forward "other"
             requests to the firewall's DNS server. (You may have already
             done this :-)

         (3) Change the resolve.conf file on the firewall to resolve off
of the
             internal mail server.

        If the above is done right, then the outside world sees the
firewall DNS,
which has the MX record pointing to the firewall.  The firewall itself
sees the
*internal* MX record, which causes sendmail on the firewall to forward
internally.
===========

I Hope this helps a little...

*** Doug Fajardo

Naresh Narang wrote:
 > Hello,
 >
 >...........Stuff truncated for brevity........
 > MX record of Internal host on the firewall box. Now the problem is: Smap
 > receives the mail from "outside" but Smapd collects the mail but
 > sendmail is not able to deliver it to internal host because it can't
 > find it.
 >...........Stuff truncated for brevity........
 >     Please tell me what mistake I am making. BTW if I specify the host
 > name in rewrite Rule 0 of Sendmail.cf, sendmail is able to correctly
 > deliver the mail. But I would like the above method to work instead of
 > this one.
 >
 > Thanks
 >
 > N.K. Narang
 > Delhi, India

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