Hello Crist,
I have implemented the recommended changes. It works forward and
reverse for the test record, from out domain or others, or for almost
all of the test records.
There are still some spurious failures, such as this one:
200 IN CNAME 200.186.198.193.dhcp.slava.alu.hr.
201 IN CNAME 201.186.198.193.dhcp.slava.alu.hr.
nslookup 193.198.186.200 works and .201 doesn't, despite the symmetric
definition:
root@domac:/etc/bind/zones# nslookup 193.198.186.200
200.186.198.193.in-addr.arpa canonical name =
200.192/27.186.198.193.in-addr.arpa.
200.192/27.186.198.193.in-addr.arpa canonical name =
200.186.198.193.dhcp.slava.alu.hr.
200.186.198.193.dhcp.slava.alu.hr name =
test-record1.slava.alu.hr.
Authoritative answers can be found from:
186.198.193.dhcp.slava.alu.hr nameserver = domac.alu.hr.
domac.alu.hr internet address = 161.53.235.3
root@domac:/etc/bind/zones# nslookup 193.198.186.201
** server can't find 201.186.198.193.in-addr.arpa: NXDOMAIN
root@domac:/etc/bind/zones#
I can't get to the bottom of this, I don't know enough BIND9
internals.
It will take real-life production load tomorrow to see how this will
behave with DHCP DDNS updates. :-)
You said ABSOLUTELY NO WARRANTY but I am an open source fan and I can
live with that ;-)
Until tomorrow, then ...
Kind regards,
Mirsad Todorovac
On 12/12/2021 10:33 AM, Mirsad Goran Todorovac wrote:
Hi Crist,
Now the resolution from the problematic record started working again
without any change in zones or BIND9 options, also without the
server process restart ... :-/
root@domac:~# nslookup -query=any
195.192/27.186.198.193.in-addr.arpa.
Server: 161.53.235.3
Address: 161.53.235.3#53
195.192/27.186.198.193.in-addr.arpa name =
test-record.slava.alu.hr.
root@domac:~# nslookup -query=ptr 193.198.186.195
Server: 161.53.235.3
Address: 161.53.235.3#53
Non-authoritative answer:
195.186.198.193.in-addr.arpa canonical name =
195.192/27.186.198.193.in-addr.arpa.
195.192/27.186.198.193.in-addr.arpa name =
test-record.slava.alu.hr.
Authoritative answers can be found from:
192/27.186.198.193.in-addr.arpa nameserver = domac.alu.hr.
domac.alu.hr internet address = 161.53.235.3
root@domac:~#
I guess this was something with timeouts. Suppose this will work
satisfactory on desktops that usually keep the same IP address
assigned by DHCP across the lease renewals, but not for laptops,
Android and iPhone devices that connect and disconnect, and change
network ...
Why I want smartphones to have reverse PTRs is to see in logs if
something becomes virus infected or even spambot, and not have to
browse DHCP leases in forensic analysis, which my fellow
administrator probably would not know how to do ...
Kind regards,
Mirsad Todorovac
On 12/12/2021 10:19 AM, Mirsad Goran Todorovac wrote:
Hi Crist,
Thank you for your explanation. It was much appreciated.
However, as I previously asserted, it is impossible to know how the
system will behave without testing it with real life production load
on Monday :-)
On 12/11/2021 11:18 PM, Crist Clark wrote:
Looks like you're trying to use the setup in that serverfault link.
That example only works on an internal network. I thought the
186.198.193. part was enough to make the zone unique. But your
assertion is correct: I would collide if any other administrators on
other subnets in range 193.198.186.0/24 decide to make reverse DHCP
DDNS update in the future. Thanks for the thought!
The point of the example I gave is that you are going to build your
own reverse zone inside of a zone you control on the Internet. Now
that you've given some examples, I can perhaps make it more obvious
what I'm suggesting. Your DNS zone would look something like,
$ORIGIN 192-27.186.198.193.in-addr.arpa.
@ IN NS domac.alu.hr [1].
@ IN NS bjesomar.srce.hr [2].
195 IN PTR test-record.dhcp.slava.alu.hr [3].
$GENERATE 200-222 $ CNAME $.186.198.193.dhcp.slava.alu.hr [4].
And your DHCP configuration,
ddns-domainname "slava.alu.hr [5]";
ddns-rev-domainname "dhcp.slaval.alu.hr [6]";
zone slava.alu.hr [5]. {
primary 127.0.0.1;
key DDNS_UPDATE;
}
NOT TESTED. NO GUARANTEES. NOT SUITABLE FOR ANY GIVEN PURPOSE. YOUR
MILEAGE MAY VARY. PLEASE CONSULT YOUR PERSONAL PHYSICIAN BEFORE
STARTING ISC PRODUCTS.
Noted. :-) I am not afraid of experimenting. But failures of the
experimental setup are perceived as my incompetence, and success taken
for granted the very next day ;-)
One other odd thing, sometimes you refer to a
"192/27.186.198.193.in-addr.arpa" zone and sometimes
"192-27.186.198.193.in-addr.arpa." Those are different names and are
not interchangeable. Both are totally fine for use in DNS, but a lot
of administrators don't like the '/' in zone names since they often
use the zone name in file names. Slashes present a problem in file
names on *nix flavored OSes. I used the dash, '-', version in my
example.
This setup is mandated from the upper level sysadmins and I cannot
control it, I can only beg them to use a hyphen as in RFC 2317 chapter
4 last paragraph, but I cannot guarantee that they will change it. It
is their arbitrary decision. :-/
Frankly, /27 is more readable, but if it creates havoc in Linux
resolver, then what the heck ...
Thank you very much again for your advice. I will post back here on
the results with your recommended zone setup.
Kind regards,
Mirsad Todorovac
Hi again,
I had some luck in making this setup work. So far, so good ...
However, there's no telling how the DHCP DDNS will function with the
new 186.198.193.dhcp. zone before Monday morning when the subsidiary
computers power up.
However, I have an odd behavior which I cannot explain: without any
change to zone a reverse resolution stopped working. The setup just
doesn't seem stable enough to work with DHCP-updated dynamic DNS in
our organization, with a lot of smartphones and wireless devices
frequently signing on and off.
The zone is:
$ORIGIN 192/27.186.198.193.in-addr.arpa.
@ IN NS domac.alu.hr [8].
;@ IN NS bjesomar.srce.hr [9].
195 IN PTR test-record.slava.alu.hr [10].
200 IN CNAME 200.186.198.193.dhcp.
201 IN CNAME 201.186.198.193.dhcp.
; MT 20211211:
; Here's the magic:
$GENERATE 202-222 $ CNAME $.186.198.193.dhcp.
The command output shows that resolution succeeds, but nslookup
can't finish it for some unknown spurious reason.
root@domac:~# nslookup -query=any
195.192/27.186.198.193.in-addr.arpa.
Server: 161.53.235.3
Address: 161.53.235.3#53
195.192/27.186.198.193.in-addr.arpa name =
test-record.slava.alu.hr [10].
root@domac:~# nslookup -query=ptr 193.198.186.195
Server: 161.53.235.3
Address: 161.53.235.3#53
** server can't find 195.186.198.193.in-addr.arpa: NXDOMAIN
root@domac:~#
This kind of setup that sometimes works and sometimes doesn't will
make me look incompetent.
I know that BIND 9 is great open source server with lots of bells
and whistles. But right now I can't study all those and I just want
to survive, providing a solution fast enough for our uplevel
sysadmins.
The /etc/bind/named.conf.local part looks like:
zone "192/27.186.198.193.in-addr.arpa" in {
type master;
file "/etc/bind/zones/192-27.186.198.193.in-addr.arpa.db";
};
zone "186.198.193.dhcp" in {
type master;
file "/var/cache/bind/186.198.193.dhcp.db";
allow-update { key DDNS_UPDATE; };
};
What possibly could be killing the name resolution between resolving
195.192/27.186.198.193.in-addr.arpa to test-record.slava.alu.hr
[10]. and resolving 193.198.186.195 that apparently fails?
Is there a way to see more interim debugging output?
Thank you very much.
Kind regards,
Mirsad Todorovac
On 12/11/2021 10:25 AM, Mirsad Goran Todorovac wrote:
Hi Crist,
Thank you for your reply and the information provided.
I have roughly implemented this workaround. I was hoping there was a
way to instruct BIND to masquerade a delegated domain with data from
another (dynamically updated from ISC DHCP) zone.
More accurately, my (from upper level) mandated delegation is the
literal 192/27.186.198.193.in-addr.arpa, using
192-27.186.198.193.in-addr.arpa says "ignoring records outside of
the origin" or something like that.
I have used the following records in the zone:
$ORIGIN 192/27.186.198.193.in-addr.arpa.
@ IN NS domac.alu.hr [8].
@ IN NS bjesomar.srce.hr [9].
195 IN PTR test-record.slava.alu.hr [10].
$GENERATE 200-222 $ CNAME $.186.198.193.dhcp.
/etc/dhcp/dhcpd.conf has this:
ddns-domainname "slava.alu.hr [7]";
ddns-rev-domainname "dhcp";
zone slava.alu.hr [7]. {
primary 127.0.0.1;
key DDNS_UPDATE;
}
zone 186.198.193.dhcp. {
primary 127.0.0.1;
key DDNS_UPDATE;
}
However, don't I have to convince people managing bjesomar.srce.hr
[9] to be a slave server for the "186.198.193.dhcp" zone? Or the
dynamically updated reverse PTR record will have effect only in my
local domain (which I had even before the entire setup), won't it?
Also, I get spurious REFUSED or NXDOMAIN errors, some pass with
time, so there must be some TTL or timeout.
Kind regards,
Mirsad
On 12/11/2021 6:04 AM, Crist Clark wrote:
No idea if this is the best way. It is a way.
Do you control any other zone? Let’s say you own
“example.com.” You can tell ISC DHCP to build the reverse zone
at an arbitrary base name instead of in-addr.arpa.
Configure DHCP to put the reverse records at say,
“rev.example.com.” So you’ll get records at,
193.186.198.193.rev.example.com [11]
194.186.198.193.rev.example.com [12]
…
And in your RFC 2317-style delegation, you then enumerate another
CNAME layer,
$ORIGIN 192-27.186.198.193.in-addr.arpa.
193 IN CNAME 193.186.198.193.rev.example.com [11].
194 IN CNAME 194.186.198.193.rev.example.com [12].
…
On Fri, Dec 10, 2021 at 2:51 PM Mirsad Goran Todorovac
<mirsad.todoro...@alu.unizg.hr> wrote:
Hello,
I have a problem with DHCP DDNS update to BIND 9 reverse PTR zone
subnet that is owned by several organizations, so I can't get a
direct DHCP DDNS update access with a key or with hostname.
I have been delegated domain name 192-27.186.198.193.in-addr.arpa
from the upper level admins, and that appears to be immutable.
However, my subnet is 193.198.186.192/27 [13], and DHCP only knows
how to perform DDNS update to 186.198.193.in-addr.arpa. (See here:
https://serverfault.com/questions/806875/how-to-tell-isc-dhcp-correct-zone-for-reverse-zone-ddns-update
and here:
https://lists.isc.org/mailman/htdig/dhcp-users/2006-August/001422.html
).
(This setup is because we have DHCP addresses that are not over NAT,
but /24 subnet is shared with other organizations, even under
another Minstry.)
I want to have the effect of delegating the same database to upper
level under their zone name, while updating the same database under
my DHCP-understood zone name.
I tried this /etc/bind/named.conf.local:
zone "192-27.186.198.193.in-addr.arpa" in {
type master;
file "/var/cache/bind/192-27.186.198.193.in-addr.arpa.db";
};
zone "186.198.193.in-addr.arpa" in {
type master;
file "/var/cache/bind/192-27.186.198.193.in-addr.arpa.db";
allow-update { key DDNS_UPDATE; };
};
(Two zones with the same file.)
What I got was:
root@domac:/etc/bind# named-checkconf
/etc/bind/named.conf.local:49: writeable file
'/var/cache/bind/192-27.186.198.193.in-addr.arpa.db': already in
use: /etc/bind/named.conf.local:44
root@domac:/etc/bind#
Can you please tell me is there a way to achieve the effect of the
above (illegal) setup?
I can't change DHCP nor I know an option to tell it to accept update
to 192-27.186.198.193.in-addr.arpa
(it is a syntax error).
The DHCP dhcpd.conf subnet configuration is:
subnet 193.198.186.192 netmask 255.255.255.224 {
range 193.198.186.200 193.198.186.222; # MT 20211210
option subnet-mask 255.255.255.224;
option domain-name-servers 161.53.235.3, 161.53.2.70;
option domain-name "slava.alu.hr [7]";
ddns-domainname "slava.alu.hr [7]";
zone slava.alu.hr [7]. {
primary 127.0.0.1;
key DDNS_UPDATE;
}
zone 186.198.193.in-addr.arpa. {
primary 127.0.0.1;
key DDNS_UPDATE;
}
option broadcast-address 193.198.186.223;
option routers 193.198.186.193;
default-lease-time 43200;
max-lease-time 86400;
}
Thank you very much for your time reading this mail and help.
Kind regards,
--
Mirsad Goran Todorovac
Academy of Fine Arts | Faculty of Graphic Arts
University of Zagreb
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Links:
------
[1] http://domac.alu.hr/
[2] http://bjesomar.srce.hr/
[3] http://test-record.slava.alu.hr/
[4] http://186.198.193.dhcp.slava.alu.hr
[5] http://slava.alu.hr/
[6] http://dhcp.slaval.alu.hr
[7] http://slava.alu.hr
[8] http://domac.alu.hr
[9] http://bjesomar.srce.hr
[10] http://test-record.slava.alu.hr
[11] http://193.186.198.193.rev.example.com
[12] http://194.186.198.193.rev.example.com
[13] http://193.198.186.192/27
