BIND 9.18.2 break-dnssec question

[Mark Andrews]

break-dnssec is about if the client could detect the re-write or not using DNSSEC.  If the client has DO=1 in the request and the normal response is signed then rewrites can be detected. If break-dnssec is ’no’ the rewrite will be prevented.  If break-dnssec is ‘yes’ then the rewrite will occur.


the world <-> recursive server rpz w/ break-dnssec no <-> recursive server rpz w/ break-dnssec no or yes;
                            |                                            |
                      non dnssec client                            non dnssec client

You don’t want the second recursive server to spend all its time re-asking queries that will fail validation

> On 29 Apr 2022, at 11:24, J Doe <general at nativemethods.com> wrote:
> 
> Hi,
> 
> I am configuring an RPZ for a validating resolver.  I read in the BIND 9.18.2 ARM that there is a boolean option for RPZ zones called: break-dnssec.
> 
> The ARM states:
> 
>    ...In that case, RPZ actions are applied regardless of DNSSEC.
>    The name of the clause option reflects the fact that results
>    rewritten by RPZ actions cannot verify.
> 
> In my particular scenario, I want to use RPZ to give NXDOMAIN results for certain domain names that I don't want accessible.  So for normal queries without DNSSEC validation requested and for queries with DNSSEC validation requested for a domain name I am _not_ blocking, I want the lookups to work (ie: don't validate when validation not requested, validate when validation requested).
> 
> When a client attempts to lookup a domain name that _is_ blocked by RPZ, I want the domain name blocked ... whether or not they requested DNSSEC validation.
> 
> Am I correct that: break-dnssec yes comes into play only if a client attempts to resolve a DNSSEC secured domain name I _am_ blocking in RPZ ?
> 
> So for instance...
> 
> 1. Client requests no validation for example.com which is not in RPZ and gets normal result.
> 
> 2. Client requests validation for example.com which is not in RPZ and gets validated result.
> 
> 3. Client requests no validation for evil.com which is in RPZ and gets NXDOMAIN result.
> 
> 4. Client requests validation for evil.com which is in RPZ and gets NXDOMAIN result with broken DNSSEC validation due to rewrite.
> 
> This would mean that: break-dnssec yes:
> 
> ...only breaks DNSSEC validation for evil.com because it is re-written
> ...does NOT break DNSSEC validation for sites _NOT_ in RPZ that use DNSSEC (ie: ietf.org).
> 
> Is that correct ?
> 
> Thanks,
> 
> - J
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Mark Andrews, ISC
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