[dns-operations] Strange Responses for 20.in-addr.arpa

[Lutz Donnerhacke]

While digging for some DNSKEYs I got not responses at all for 20.in-addr.arpa.
Deeper inspections shows, that those servers response only to queries for
NS, PTR and (sometimes) SOA.

Example:

; <<>> DiG 9.4.0 <<>> soa 20.in-addr.arpa
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 51467
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

; <<>> DiG 9.4.0 <<>> soa 6.20.in-addr.arpa
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28585
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2
6.20.in-addr.arpa.	86400	IN	SOA	ns2.csc.com. dnsadmi...

; <<>> DiG 9.4.0 <<>> dnskey 6.20.in-addr.arpa
;; global options:  printcmd
;; connection timed out; no servers could be reached

; <<>> DiG 9.4.0 <<>> ptr 1.1.6.20.in-addr.arpa
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 13228
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2
1.1.6.20.in-addr.arpa.	86400	IN	PTR	nwkcat91-v21v.de-wil.csc.com.


I do not understand this, but assume the setup is correct.