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"forward first" set on a master zone not working as expected

From Taylor Vierrether@21:1/5 to All on Wed Sep 2 11:00:38 2020

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Hello,

I am attempting to set up an internal DNS server that is authoritative for internal resources, but also will respond for external resources on the same domain that it does not have records for.

For example, I have a domain sub.example.com <http://sub.example.com/>, and I want to have internal entries in the BIND zone file for host1.sub.example.com <http://host1.sub.example.com/> and host2.sub.example.com <http://host2.sub.example.com/>. That
part is working fine. However, there is a publicly available DNS entry for sub.example.com <http://sub.example.com/> that I want my internal clients to be able to resolve, but I don’t want to have the IP in the BIND zone file, because the IP is dynamic.
There are also some hosts (host3.sub.example.com <http://host3.sub.example.com/>) and (host4.sub.example.com <http://host4.sub.example.com/>) that are externally resolvable that I don’t want to put in my internal BIND file because they are not
controlled by me. (Think CNAME to a SaaS application)

I’ve attempted to do this as follows, and it seems to make sense that it would work, but it does not.

named.conf:

zone “sub.example.com" IN {
type master;
file "/etc/bind/sub.example.com.zone";
forward first;
forwarders { 1.1.1.1; 1.0.0.1; };
};

sub.example.com <http://sub.example.com/>.zone:

$ORIGIN sub.example.com.
$ttl 600
@ 300 SOA dns.sub.example.com. (
taylor.viertaxa.com. ; address of responsible party
2020090101 ; serial number
300 ; refresh period
300 ; retry period
604800 ; expire time
300 ) ; minimum ttl
300 NS elinore.ns.cloudflare.com.
300 NS hal.ns.cloudflare.com.
host1 60 A 10.x.x.x
host2 60 A 10.x.x.x

What I would expect to happen, is that BIND sees “forward first” and attempts to look up the hostname host3.sub.example.com <http://host3.sub.example.com/> on the listed forwarders, and succeeds (there’s an entry publicly available for that one.

What actually happens, is if I query for sub.example.com <http://sub.example.com/> I get the following from nslookup:
*** Can't find sub.example.com: No answer

And if I query for host3.example.com <http://host3.example.com/>, I get the following from nslookup:
** server can't find host3.sub.example.com: NXDOMAIN

BIND version:

Package: bind9
Version: 1:9.11.5.P4+dfsg-5.1+deb10u2

Thank you in advance for any help you might be able to provide. --Apple-Mail=_02FE9945-4A58-4CA7-A3A2-379138347C24
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Content-Type: text/html; charset=utf-8

<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hello,<div class=""><br class=""></div><div class="">I am
attempting to set up an internal DNS server that is authoritative for internal resources, but also will respond for external resources on the same domain that it does not have records for.</div><div class=""><br class=""></div><div class="">For example,
I have a domain <a href="http://sub.example.com" class="">sub.example.com</a>, and I want to have internal entries in the BIND zone file for <a href="http://host1.sub.example.com" class="">host1.sub.example.com</a> and <a href="http://host2.sub.
example.com" class="">host2.sub.example.com</a>. That part is working fine. However, there is a publicly available DNS entry for <a href="http://sub.example.com" class="">sub.example.com</a> that I want my internal clients to be able to resolve, but
I don’t want to have the IP in the BIND zone file, because the IP is dynamic. There are also some hosts (<a href="http://host3.sub.example.com" class="">host3.sub.example.com</a>) and (<a href="http://host4.sub.example.com" class="">host4.sub.example.
com</a>) that are externally resolvable that I don’t want to put in my internal BIND file because they are not controlled by me. (Think CNAME to a SaaS application)</div><div class=""><br class=""></div><div class="">I’ve attempted to do this as
follows, and it seems to make sense that it would work, but it does not. </div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">named.conf:</div><div class=""><br class=""></div><div class=""><div class="">zone “<a
href="http://sub.example.com" class="">sub.example.com</a>" IN {</div><div class="">        type master;</div><div class="">        file "/etc/bind/sub.example.com.zone";</div><div class="">      &
nbsp; forward first;</div><div class="">        forwarders { 1.1.1.1; 1.0.0.1; };</div><div class="">};</div></div><div class=""><br class=""></div><div class=""><a href="http://sub.example.com" class="">sub.example.com</a>.zone:</div>
<div class=""><br class=""></div><div class=""><div class="">$ORIGIN <a href="http://sub.example.com" class="">sub.example.com</a>.</div><div class="">$ttl 600</div><div class="">@                     &
nbsp;300 SOA   <a href="http://dns.sub.example.com" class="">dns.sub.example.com</a>. (</div><div class="">                              <a href="http://taylor.viertaxa.com"
class="">taylor.viertaxa.com</a>.      ; address of responsible party</div><div class="">                              2020090101          
     ; serial number</div><div class="">                              300                       ; refresh
period</div><div class="">                              300                       ; retry period</div><div class="">  &
nbsp;                           604800                    ; expire time</div><div class="">             
                300                     ) ; minimum ttl</div><div class="">                      300 NS  
 <a href="http://elinore.ns.cloudflare.com" class="">elinore.ns.cloudflare.com</a>.</div><div class="">                      300 NS    <a href="http://hal.ns.cloudflare.com" class="">
hal.ns.cloudflare.com</a>.</div><div class="">host1                   60  A     10.x.x.x</div><div class="">host2                   60  A  
  10.x.x.x</div></div><div class=""><br class=""></div><div class="">What I would expect to happen, is that BIND sees “forward first” and attempts to look up the hostname <a href="http://host3.sub.example.com" class="">host3.sub.example.com</a>&
nbsp;on the listed forwarders, and succeeds (there’s an entry publicly available for that one. </div><div class=""><br class=""></div><div class="">What actually happens, is if I query for <a href="http://sub.example.com" class="">sub.example.com</

 I get the following from nslookup:</div><div class="">*** Can't find <a href="http://sub.example.com" class="">sub.example.com</a>: No answer</div><div class=""><br class=""></div><div class="">And if I query for <a href="http://host3.example.com"

class="">host3.example.com</a>, I get the following from nslookup:</div><div class="">** server can't find <a href="http://host3.sub.example.com" class="">host3.sub.example.com</a>: NXDOMAIN</div><div class=""><br class=""></div><div class=""><br class="
"></div><div class="">BIND version:</div><div class=""><br class=""></div><div class=""><div class="">Package: bind9</div><div class="">Version: 1:9.11.5.P4+dfsg-5.1+deb10u2</div></div><div class=""><br class=""></div><div class=""><br class=""></div><
div class="">Thank you in advance for any help you might be able to provide. </div></body></html>
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From Matus UHLAR - fantomas@21:1/5 to Taylor Vierrether via bind-users on Thu Sep 3 09:51:28 2020

On 02.09.20 15:00, Taylor Vierrether via bind-users wrote:

I am attempting to set up an internal DNS server that is authoritative for internal resources, but also will respond for external resources on the
same domain that it does not have records for.

For example, I have a domain sub.example.com , and I want to have internal entries in the BIND zone file for host1.sub.example.com and host2.sub.example.com. That part is working fine. However, there is a publicly available DNS entry for sub.example.com that I want my internal clients to be able to resolve, but I don’t want to have the IP in the BIND zone file, because the IP is dynamic.

you can delegate that entry elsewhere.

There are also some hosts (host3.sub.example.com ) and (host4.sub.example.com) that are externally resolvable that I don’t want
to put in my internal BIND file because they are not controlled by me.
(Think CNAME to a SaaS application)

you can delegate those records somewhere.

I’ve attempted to do this as follows, and it seems to make sense that it
would work, but it does not.

named.conf:

zone “sub.example.com" IN {
type master;
file "/etc/bind/sub.example.com.zone";
forward first;
forwarders { 1.1.1.1; 1.0.0.1; };
};

forwarding is not used for zone other than "type forward".

What actually happens, is if I query for sub.example.com I get the following from nslookup:
*** Can't find sub.example.com: No answer

if you search for "sub.example.com" record, you can not delegate that one,
of course.

you apparently should use redesign your DNS. Easiest way would be using different domain internally.

And if I query for host3.example.com , I get the following from nslookup:
** server can't find host3.sub.example.com: NXDOMAIN

note that nslookup is very bad program for tracking DNS errors.
use "host" or "dig" for that case.

--
Matus UHLAR - fantomas, uhlar@fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
I just got lost in thought. It was unfamiliar territory.

--- SoupGate-Win32 v1.05
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From Kevin Darcy@21:1/5 to ML BIND Users on Thu Sep 3 09:00:56 2020

[ Classification Level: GENERAL BUSINESS ]

Or, if you absolutely *must* use the same namespace internally and
externally (oftentimes you can't talk the business out of that), your
internal version should be a more-or-less a superset of your external
version.

How you keep those in sync is up to you. For us, we have a centralized management system that makes the relevant updates in parallel. The big
caveat with that is, those few situations where the DNS needs to be "schizophrenic", i.e. resolve differently in the internal versus external versions of the zones. We try to keep that nonsense to a minimum, but when
we can't talk people out of it, we handle it on an exception basis.

I suppose another approach is to have a backend database which tags each
record as being "internal", "external" or "both", and then the respective versions of the zones get generated accordingly. You'd need something to
ensure referential integrity, though, otherwise you might end up with
dangling references (e.g. CNAME/MX/SRV targets), bad delegations, etc.

- Kevin

P.S. No offense to schizophrenics. I guess a more accurate term would be "multiple personality".

On Thu, Sep 3, 2020 at 3:52 AM Matus UHLAR - fantomas <uhlar@fantomas.sk> wrote:

On 02.09.20 15:00, Taylor Vierrether via bind-users wrote:

I am attempting to set up an internal DNS server that is authoritative

for

internal resources, but also will respond for external resources on the same domain that it does not have records for.

For example, I have a domain sub.example.com , and I want to have

internal

entries in the BIND zone file for host1.sub.example.com and host2.sub.example.com. That part is working fine. However, there is a publicly available DNS entry for sub.example.com that I want my internal clients to be able to resolve, but I don’t want to have the IP in the

BIND

zone file, because the IP is dynamic.

you can delegate that entry elsewhere.

There are also some hosts (host3.sub.example.com ) and (host4.sub.example.com) that are externally resolvable that I don’t want to put in my internal BIND file because they are not controlled by me. (Think CNAME to a SaaS application)

you can delegate those records somewhere.

I’ve attempted to do this as follows, and it seems to make sense that it
would work, but it does not.

named.conf:

zone “sub.example.com" IN {
type master;
file "/etc/bind/sub.example.com.zone";
forward first;
forwarders { 1.1.1.1; 1.0.0.1; };
};

forwarding is not used for zone other than "type forward".

What actually happens, is if I query for sub.example.com I get the

following from nslookup:

*** Can't find sub.example.com: No answer

if you search for "sub.example.com" record, you can not delegate that one,
of course.

you apparently should use redesign your DNS. Easiest way would be using different domain internally.

And if I query for host3.example.com , I get the following from nslookup: >** server can't find host3.sub.example.com: NXDOMAIN

note that nslookup is very bad program for tracking DNS errors.
use "host" or "dig" for that case.

--
Matus UHLAR - fantomas, uhlar@fantomas.sk ; http://www.fantomas.sk/
Warning: I wish NOT to receive e-mail advertising to this address.
Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.
I just got lost in thought. It was unfamiliar territory. _______________________________________________
Please visit https://lists.isc.org/mailman/listinfo/bind-users to
unsubscribe from this list

ISC funds the development of this software with paid support
subscriptions. Contact us at https://www.isc.org/contact/ for more information.

bind-users mailing list
bind-users@lists.isc.org
https://lists.isc.org/mailman/listinfo/bind-users

<div dir="ltr"><div>[ Classification Level: <font color="blue">GENERAL BUSINESS</font> ]</div><br class="cursAfter">Or, if you absolutely *must* use the same namespace internally and externally (oftentimes you can't talk the business out of that),
your internal version should be a more-or-less a superset of your external version.<div><br></div><div>How you keep those in sync is up to you. For us, we have a centralized management system that makes the relevant updates in parallel. The big caveat
with that is, those few situations where the DNS needs to be "schizophrenic", i.e. resolve differently in the internal versus external versions of the zones. We try to keep that nonsense to a minimum, but when we can't talk people out of it,
we handle it on an exception basis.</div><div><br></div><div>I suppose another approach is to have a backend database which tags each record as being "internal", "external" or "both", and then the respective versions of
the zones get generated accordingly. You'd need something to ensure referential integrity, though, otherwise you might end up with dangling references (e.g. CNAME/MX/SRV targets), bad delegations, etc.</div><div><br></div><div>
- Kevin</div><div><br></div><div>P.S. No offense to schizophrenics. I guess a more accurate term would be "multiple personality".</

<div><br><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Sep 3, 2020 at 3:52 AM Matus UHLAR - fantomas <<a href="mailto:uhlar@fantomas.sk">uhlar@fantomas.sk</a>> wrote:<br></div><blockquote class="gmail_quote" style="

margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">On 02.09.20 15:00, Taylor Vierrether via bind-users wrote:<br>
> I am attempting to set up an internal DNS server that is authoritative for<br>
> internal resources, but also will respond for external resources on the<br>
> same domain that it does not have records for.<br>
><br>
> For example, I have a domain <a href="http://sub.example.com" rel="noreferrer" target="_blank">sub.example.com</a> , and I want to have internal<br>
> entries in the BIND zone file for <a href="http://host1.sub.example.com" rel="noreferrer" target="_blank">host1.sub.example.com</a> and<br>
> <a href="http://host2.sub.example.com" rel="noreferrer" target="_blank">host2.sub.example.com</a>. That part is working fine. However, there is a<br>
> publicly available DNS entry for <a href="http://sub.example.com" rel="noreferrer" target="_blank">sub.example.com</a> that I want my internal<br>
> clients to be able to resolve, but I don’t want to have the IP in the BIND<br>
> zone file, because the IP is dynamic.<br>

you can delegate that entry elsewhere.<br>

> There are also some hosts (<a href="http://host3.sub.example.com" rel="noreferrer" target="_blank">host3.sub.example.com</a> ) and<br>
> (<a href="http://host4.sub.example.com" rel="noreferrer" target="_blank">host4.sub.example.com</a>) that are externally resolvable that I don’t want<br>
> to put in my internal BIND file because they are not controlled by me. <br>
> (Think CNAME to a SaaS application)<br>

you can delegate those records somewhere.<br>

>I’ve attempted to do this as follows, and it seems to make sense that it<br>
> would work, but it does not.<br>
><br>
><br>
>named.conf:<br>
><br>
>zone “<a href="http://sub.example.com" rel="noreferrer" target="_blank">sub.example.com</a>" IN {<br>
> type master;<br>
> file "/etc/bind/<a href="http://sub.example.com" target="_blank">sub.example.com</a>.zone";<br>
> forward first;<br>
> forwarders { 1.1.1.1; 1.0.0.1; };<br>
>};<br>

forwarding is not used for zone other than "type forward".<br>

>What actually happens, is if I query for <a href="http://sub.example.com" rel="noreferrer" target="_blank">sub.example.com</a> I get the following from nslookup:<br>
>*** Can't find <a href="http://sub.example.com" rel="noreferrer" target="_blank">sub.example.com</a>: No answer<br>

if you search for "<a href="http://sub.example.com" rel="noreferrer" target="_blank">sub.example.com</a>" record, you can not delegate that one,<br>
of course.<br>

you apparently should use redesign your DNS. Easiest way would be using<br> different domain internally.<br>

>And if I query for <a href="http://host3.example.com" rel="noreferrer" target="_blank">host3.example.com</a> , I get the following from nslookup:<br>
>** server can't find <a href="http://host3.sub.example.com" rel="noreferrer" target="_blank">host3.sub.example.com</a>: NXDOMAIN<br>

note that nslookup is very bad program for tracking DNS errors.<br>
use "host" or "dig" for that case.<br>

-- <br>
Matus UHLAR - fantomas, <a href="mailto:uhlar@fantomas.sk" target="_blank">uhlar@fantomas.sk</a> ; <a href="http://www.fantomas.sk/" rel="noreferrer" target="_blank">http://www.fantomas.sk/</a><br>
Warning: I wish NOT to receive e-mail advertising to this address.<br> Varovanie: na tuto adresu chcem NEDOSTAVAT akukolvek reklamnu postu.<br>
I just got lost in thought. It was unfamiliar territory.<br> _______________________________________________<br>
Please visit <a href="https://lists.isc.org/mailman/listinfo/bind-users" rel="noreferrer" target="_blank">https://lists.isc.org/mailman/listinfo/bind-users</a> to unsubscribe from this list<br>

ISC funds the development of this software with paid support subscriptions. Contact us at <a href="https://www.isc.org/contact/" rel="noreferrer" target="_blank">https://www.isc.org/contact/</a> for more information.<br>

bind-users mailing list<br>
<a href="mailto:bind-users@lists.isc.org" target="_blank">bind-users@lists.isc.org</a><br>
<a href="https://lists.isc.org/mailman/listinfo/bind-users" rel="noreferrer" target="_blank">https://lists.isc.org/mailman/listinfo/bind-users</a><br>
</blockquote></div></div></div>

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"forward first" set on a master zone not working as expected

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