rbldnsd and DNSSEC compatibility issues - any suggestions?

Rob McEwen rob at invaluement.com
Fri Sep 11 05:04:22 UTC 2020


The whole usage of DNS by the anti-spam industry in our DNSBLs - is 
somewhat a hack on the DNS system from the start - I guess if you think 
that is wrong, maybe you should take that up with Paul Vixie?

And the whole purpose for MANY of us DNSBLs using ".local" in the first 
place - was precisely to PREVENT the queries from possibly leaking out 
of our largest customers LANs  - because in many cases, that would an 
essential denial of service attack against us (and our hosters, etc). 
For example, some DNSBL customers literally have a billion mailboxes. I 
have a couple of customers with a few hundreds million mailboxes. I'm 
pretty sure Spamhaus has a few with a billion. Do you have any idea how 
many emails are processed per second for a billion mailboxes? 
(especially mid-morning during a business day!) It's enough to where it 
takes multiple rbldnsd servers each serving thousands of queries per 
second. To keep up with that volume, these MUST be locally-hosted 
rbldsnd servers. In that situation, if/when there is a slight DNS 
mistake - such as some software update mistakenly rerouting DNS to 
something like "" - as OFTEN (stupidly!) happens - and then, in 
the case of Spamhaus' customers with a billion mailboxes - that traffic 
will massively hit both Google and "spamhaus.org" DNS servers - or even 
if the forwarder got deleted mistakenly, the same will still happen for 
"spamhaus.org" DNS servers. Even if those servers can handle the traffic 
- it might overwhelm a local router in between, or overwhelm the 
particular DNS server to which this traffic is assigned. This then turns 
into a NIGHTMARE DOS attack for such DNSBLs. Therefore, the ENTIRE point 
of using such zone names (".local", ".dnsbl", etc) internally - is to 
PREVENT the queries from possibly ever leaving the LAN. That is why, for 
these largest customers, using hostnames that end in our own domain 
names - is not an option. (and when it does work, it is often a "let 
them eat cake" option - where only the largest Internet companies with 
billions in revenue - can afford to handle such traffic - so please, 
don't respond with a "let them eat cake" answer!) But that overall point 
about how DNSBLs work in such situations... seems lost on you.

The very reason I used ".dnsbl" as an example - is because I did a 
little research after before last email - and it turns out that - maybe 
in response to the RFC you pointed out that took a position against 
using ".local" - Spamhaus then (apparently) switched to using ".dnsbl" - 
(or maybe they were using ".dnsbl" all along? - I can't keep track over 
every other DNSBL - but ".local" was popular for many DNSBLs for many 
years.) Spamhaus doesn't use that for their direct query service - but 
it appears that they're using that for the instructions for their 
customers who RSYNC the data. Therefore, you just harshly criticized me 
for suggesting doing what Spamhaus ALREADY does - so I guess I'm in good 

Really - your purism - and harsh realities of large DSNBL operations - 
are not compatible.

And no - you NEVER gave me an answer - and guess what? While I have 
tremendous respect for RFCs in general, and try hard to follow them - 
they are NOT perfect - on rare occasion, some of them SHOULD be broken 
and DO have errors or situations that they didn't anticipate. This one 
of those. RFCs were written by humans. Humans make mistakes.

And it's too bad that the maintainers of BIND didn't anticipate that 
there might be local-data situations where sys admins should be given 
the ability to turn DNSSEC off for a particular zone. Your answers are 
helping me to understand HOW/WHY such decisions were made. But 
rigidity/purity doesn't always equal wisdom/intelligence. In this case, 
it doesn't.

Rob McEwen, invaluement

On 9/10/2020 10:23 PM, Mark Andrews wrote:
>> On 11 Sep 2020, at 11:13, Rob McEwen <rob at invaluement.com> wrote:
>> Mark,
>> Most invaluement subscribers do direct queries - to hostnames that end with my own valid domain names that don't have this DNSSEC issue - those are the ONE ones that make use of public DNS and are broadcast across the internet.
>> Our usage of ".local" zones for those who are RSYNC'ing our data - dates back to something like 2007, and the RFC you referred to is from 2013. By the time this RFC had been published, we'd already had customer using the ".local" for 6 years. At the time that came out in 2013, I assessed whether I needed to get my clients to change that, but it didn't seem to effect anyone. Again, those of our subscribers who RSYNC our data and use the ".local" zone names - are just using that for 100% local usage, and are not trying to broadcast it across the internet. And in many of THOSE cases, if the BIND and RBLDND are on the same computer, as is often the case, it doesn't even go out to the LAN - this is all on one single computer.
> And you squatted on .local then and are paying the price now.  It has always been wrong to use a name that has not been delegated to you.  The point of having delegations in the DNS is to prevent multiple entities using the same name and to give certainty to those the name is delegated to.  That has been the case since the DNS was developed.
> As for not leaving the machine, that machine is connected to a network where mDNS may be in use.  That creates a namespace collision on that machine.  What does invaluement.local mean on the machine?  Does the machine use mDNS or DNS to resolve the name?
>> So are you claiming that if I simply changed the zone naming form ending in ".local" - to something else - such as ".dnsbl" - then all my problems would go away? And the forwarder will start working? (even though rbldnsd doesn't do DNSSEC)
> No.  You have not been delegated ".dnsbl”.  IANA/ICANN owns *every* possible tld name not delegated / allocated to someone/something else.  Any TLD that you pick will have the same issue.  DNSSEC proves what exists, what doesn’t exist, and what isn’t secured by DNSSEC.
> You have a effectively infinite number of names below invaluement.com.  Pick some of them and use them. invaluement.com isn’t signed so your customers won’t have DNSSEC problems.  When you decide you want to sign invaluement.com you will need to break the DNSSEC chain of trust by having a delegation in the invaluement.com which doesn’t have a DS record with it.
>> That would be EXCELLENT news! Or, if that doesn't actually fix my problem, do you have any suggestions that actually address my actual question?
> I gave you a answer.  See below.
> Mark
>> Rob McEwen
>> On 9/10/2020 7:37 PM, Mark Andrews wrote:
>>> .local is for mDNS (RFC 6762).  Do not use it for other purposes as you are hijacking the namespace.
>>> The best solution is to NOT change the name of the zones from those that you use publicly.  That way they have the correct DNSSEC chain of trust down from the root.  If you want to use different zone names then create delegations to empty unsigned zones (SOA and NS records only) like those done for 10.IN-ADDR.ARPA in a zone you control.  That breaks the DNSSEC chain of trust at the delegation point.  If you later decide you want to sign these zones you can do so and link them into the DNSSEC chain of trust. Just sign both the rbldsnd-formatted files and the empty zones.
>>> If you absolutely must continue to hijack the .local namespace, which is allocated for a different purpose, then add validate-except entries to named.conf
>>> Mark
>>>> On 11 Sep 2020, at 01:56, Rob McEwen <rob at invaluement.com> wrote:
>>>> I manage an anti-spam DNSBL and I've been running into an issue in recent years - that I'm FINALLY getting around to asking about. I just joined this list to ask this question. Also, I checked the archives, but couldn't find an answer - at least, not one I understood.
>>>> So basically, while most of our users do direct queries and don't have this issue - some of our larger subscribers RSYNC the rbldsnd-formatted files, and then they typically run rbldnsd on the same server as their BIND server that is answering their DNSBL queries. Then, their invaluement zone names will all end with "invaluement.local". Typically, their RBLDNSD server is set up to listen on - and then they use BIND for answering their DNSBL queries, and so they tell BIND to get its answers for THOSE invaluement dnsbl queries by doing a DNS forwarder, telling bind to get the answers for THOSE zones from - as shown below:
>>>> zone "invaluement.local" in {
>>>>    type forward;
>>>>    forward only;
>>>>    forwarders {; };
>>>> };
>>>> This works perfectly - so long as DNSSEC is turned off. And since most of our subscribers are running a dedicated instance of BIND that is ONLY used for DNSBL queries, they don't mind turning DNSSEC off.
>>>> But, occasionally, we have a customer who cannot turn DNSSEC off. So I was hoping that THIS command would work:
>>>> dnssec-must-be-secure "invaluement.local" no;
>>>> But it doesn't seem to be helping at all. Is that command suppose to disable DNSSEC checking for a particular zone? If yes, what did I do wrong? If not, what does "dnssec-must-be-secure" set to "no" do?
>>>> I've heard that there is NOT a way to get this to work - and that such subscribers much use DNS Delegation, instead. But I really wish         this could be done by simply turning off DNSSEC for a particular zone. That could be useful for MANY various types of internal zones that need this. But if this is that case, how would that DNS Delegation look, to get the above forwarding example to work using delegation instead?
>>>> Thanks in advance for your help!
>>>> -- 
>>>> Rob McEwen, invaluement
>>>> _______________________________________________
>>>> 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 at lists.isc.org
>>>> https://lists.isc.org/mailman/listinfo/bind-users
>> -- 
>> Rob McEwen
>> https://www.invaluement.com
>> +1 (478) 475-9032

Rob McEwen
+1 (478) 475-9032

More information about the bind-users mailing list