Re: DNSSEC & WIldcards

15 Mar 2024

      Dennis Burgess via NANOG <nanog@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@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@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

Re: DNSSEC & WIldcards

Bjørn Mork