DNSSEC & WIldcards

Fri Mar 15 18:02:45 UTC 2024

Wildcards and DNSSEC work fine as long as the nameserver vendor has not stuffed up. Too many vendors play fast and loose with the DNS protocol.  Getting this correct is not hard but you do need to test before shipping.  Additionally OS vendors tend to be way behind current releases from the nameserver vendors. 

-- 
Mark Andrews

> On 16 Mar 2024, at 04:33, Bjørn Mork <bjorn at mork.no> wrote:
> 
> Dennis Burgess via NANOG <nanog at nanog.org> writes:
> 
>> So have *.app.linktechs.net that I have been trying to get to work, we
>> have DNSSEC on this, and its failing, but cannot for the life of me
>> understand why.  I think it may have something to do with proving it
>> exists as a wildcard, but any DNSSEC experts want to take a stab at it
>> ?
> 
> Not an expert, but Google knows the answer (as always :-)
> 
> bjorn at miraculix:~$ dig a www.app.linktechs.net. +dnssec +multiline @8.8.8.8
> 
> ; <<>> DiG 9.18.24-1-Debian <<>> a www.app.linktechs.net. +dnssec +multiline @8.8.8.8
> ;; global options: +cmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 65184
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1
> 
> ;; OPT PSEUDOSECTION:
> ; EDNS: version: 0, flags: do; udp: 512
> ; EDE: 10 (RRSIGs Missing): (For _acme-challenge.app.linktechs.net/nsec)
> ;; QUESTION SECTION:
> ;www.app.linktechs.net. IN A
> 
> ;; Query time: 156 msec
> ;; SERVER: 8.8.8.8#53(8.8.8.8) (UDP)
> ;; WHEN: Fri Mar 15 18:26:16 CET 2024
> ;; MSG SIZE  rcvd: 98
> 
> 
> 
> And they're right.  Your server includes the epected NSEC record, but
> leaves out the associated RRSIG.  Compare this to the
> https://datatracker.ietf.org/doc/html/rfc7129#section-5.3 example:
> 
> 
> bjorn at miraculix:~$ dig a www.app.linktechs.net. +dnssec +multiline @139.60.210.20 
> 
> ; <<>> DiG 9.18.24-1-Debian <<>> a www.app.linktechs.net. +dnssec +multiline @139.60.210.20
> ;; global options: +cmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11828
> ;; flags: qr aa rd; QUERY: 1, ANSWER: 3, AUTHORITY: 1, ADDITIONAL: 1
> ;; WARNING: recursion requested but not available
> 
> ;; OPT PSEUDOSECTION:
> ; EDNS: version: 0, flags: do; udp: 1280
> ;; QUESTION SECTION:
> ;www.app.linktechs.net. IN A
> 
> ;; ANSWER SECTION:
> www.app.linktechs.net.  3600 IN A 139.60.210.81
> www.app.linktechs.net.  3600 IN RRSIG A 8 3 3600 (
>                                20240427232616 20240313222616 37041 linktechs.net.
>                                NYC/4H2VZg12vj+tiWVkEROhXwm7JkBna6RQg6LO8kXr
>                                oosDUpGnxrgOtJYsWYbYfM58opiC1OeAbcaCB9+nctIU
>                                grrwcpuhmvlXYLZi1n/oAmelPldnQ6Hf93HuHi4ULFsS
>                                Qfsoo8sdfjt/YSJ4WxjmsM9LMbZ2CZPMU44a3MdftGW1
>                                fNKmZ1fLtVreP41KmvP6b01lyUMvjrvT26Yq57DgUDTo
>                                iqU5skT+OHzx6ERJkt3tzzwm2pBMvBWFDXC668NtouIW
>                                s3mrhJRBuNW3xSCsroaLQ0vmdml2BqNNh7MZNc38FNMJ
>                                eh+ts3mbMnOOkzlI1Q8gKMMCWv+VRmv2DA== )
> www.app.linktechs.net.  3600 IN RRSIG A 8 3 3600 (
>                                20240427232616 20240313222616 11340 linktechs.net.
>                                Th3OcZwOMNUb1zMdipnTnFdgFEaOGJ/VofQOTyxmnNCg
>                                wl+1Q7eiQ89KHAWEDBisxd0S+EHu6/YBWY2srNx5q58P
>                                XIZJ9oQXCqDLzSE884DTQNDEVrSMoKJ9slRU4N4Lj5tT
>                                9LzbODmCM9ytRavOKXJHIddQa0MZT4p9cV8K2HI7XSFX
>                                0rjieKFa7wDRJqhKyqrT3Rh/S93pavhKWUgN3GVO6hkI
>                                H5F67UFpZK7o7nRlyqvM42ep5XaRZS/WJtLuXcTk/QM3
>                                MBPTDWgJ0Bh8qpNuHDOb2XFH2I5dwjeKxuYCzeQzN1hL
>                                gsmw3d1J2pNsYbC40jmi1bZr0bz2fDurIA== )
> 
> ;; AUTHORITY SECTION:
> _acme-challenge.app.linktechs.net. 1200 IN NSEC auto.linktechs.net. TXT RRSIG NSEC
> 
> ;; Query time: 120 msec
> ;; SERVER: 139.60.210.20#53(139.60.210.20) (UDP)
> ;; WHEN: Fri Mar 15 18:27:13 CET 2024
> ;; MSG SIZE  rcvd: 724
> 
> 
> 
> Lots of resolvers will probably just look up that NSEC, get the RRSIG
> and be happy with that.  But your problem is that there always will be a
> number of resolvers not doing that.  So you get arbitrary failures.
> 
> I believe there are so many examples of really bad fallout due to
> wildcards combined with DNSSEC that it's advisable to stay away. Do one
> or the other.  Not both.
> 
> 
> 
> Bjørn