Subject: Split DNS.

From: Naresh Narang <[email-masked]>
Date: Thu, 20 Jan 2000 10:58:45 +0530

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Hello,

    I installed Split DNS on two RH Linux 5.2 boxes. One is the firewall
and other is internal host. Internal one is having complete info about
all the addresses in the network and as expected, firewall host is
having only those addresses given by Internic. I have also mentioned the
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. The address of internal box is not there is *forward or
*reverse file but I have mentioned it in the /etc/hosts file.

The MX record on firewall box is like this:

*.foo.com    IN    MX    10   host.foo.com

    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

---

From: Doug Fajardo <[email-masked]>
Date: Thu, 20 Jan 2000 00:39:40 -0800

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........
> find it.
>...........Stuff truncated for brevity........

---

From: Jussi Torhonen <[email-masked]>
Date: Thu, 20 Jan 2000 11:01:51 +0200 (EET)

> "our.internal.mail.host" via the smtp mailer.

See http://www.sendmail.org/m4/mailertables.html

You must use square brackets to setup an static SMTP route to that host.
Otherwise sendmail tries to find MX recored for your.internal.mail.host
and sure they're not available. So

#
# [email-masked] routed to some.other.internal.mail.host
qwerty.foo.com     smtp:[some.other.internal.mail.host]
#
# [email-masked] and [email-masked] routed to
# your.internal.mail.host
.foo.com           smtp:[your.internal.mail.host]
#

is a good choice. Then put your.internal.mail.host and
some.other.internal.mail.host into /etc/hosts file.

Jussi

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