ISC-DHCP and BIND 9 DNS: DDNS update fails for /27 subnet P.S.
Crist Clark
cjc+bind-users at pumpky.net
Mon Dec 13 06:10:21 UTC 2021
First, for troubleshooting, do not use nslookup(1). If you have BIND,
use dig(1) and host(1).
Since these names are out there on the Internet, we can troubleshoot
too!
I'm noticing a problem with the delegation for the
192/27.186.198.193.in-addr.arpa zone. The servers for
186.198.193.in-addr.arpa,
dns1.CARNet.hr
dns2.CARNet.hr
Return these two DNS servers,
$ dig -x 193.198.186.192/27 ns @dns1.carnet.hr
; <<>> DiG 9.16.22 <<>> -x 193.198.186.192/27 ns @dns1.carnet.hr
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8342
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;192/27.186.198.193.in-addr.arpa. IN NS
;; AUTHORITY SECTION:
192/27.186.198.193.in-addr.arpa. 14400 IN NS bjesomar.srce.hr.
192/27.186.198.193.in-addr.arpa. 14400 IN NS domac.alu.hr.
;; Query time: 182 msec
;; SERVER: 2001:b68:ff:2::2#53(2001:b68:ff:2::2)
;; WHEN: Sun Dec 12 22:03:39 PST 2021
;; MSG SIZE rcvd: 114
However, if I check that against those servers, domac.alu.hr works
(although it only returns itself as authoritative for the domain), and
bjsomar.srce.hr sends a REFUSED response,
dig -x 193.198.186.192/27 ns @bjesomar.srce.hr
; <<>> DiG 9.16.22 <<>> -x 193.198.186.192/27 ns @bjesomar.srce.hr
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: REFUSED, id: 43941
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
; COOKIE: 341626673209a23b4777d39761b6e2f9656e01a40d454dcd (good)
;; QUESTION SECTION:
;192/27.186.198.193.in-addr.arpa. IN NS
;; Query time: 181 msec
;; SERVER: 2001:b68:c:2::70:0#53(2001:b68:c:2::70:0)
;; WHEN: Sun Dec 12 22:06:50 PST 2021
;; MSG SIZE rcvd: 88
On 2021-12-12 06:45, Mirsad Goran Todorovac wrote:
> 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 at 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 at domac:/etc/bind/zones# nslookup 193.198.186.201
> ** server can't find 201.186.198.193.in-addr.arpa: NXDOMAIN
>
> root at 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 at 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 at 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 at 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 at 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 at 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 at 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.todorovac at 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 at 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 at 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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>>
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>
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>
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> unsubscribe from this list
>
> ISC funds the development of this software with paid support
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> information.
>
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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
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