I've been looking into DNS quite a bit lately and currently got the following error message with the DIG command:
BAD (HORIZONTAL) REFERRAL
From my understanding, this is caused due to delegating a name lookup without traversing down the "DNS tree". Different to a vertical referral, which delegates down the "DNS tree", a horizontal referral delegates names like the following:
(Made-up example answer from the nameserver of the zone "google.com")
;; QUESTION SECTION:
;123.google.com. IN A
;; AUTHORITY SECTION:
a.123.google.com. 7200 IN NS ns1.321.google.com.
a.123.google.com. 7200 IN NS ns2.321.google.com.
a.123.google.com. 7200 IN NS ns3.321.google.com.
When you ask one of the above specified nameservers, the following answer is returned:
;; QUESTION SECTION:
;123.google.com. IN A
;; AUTHORITY SECTION:
a.123.google.com. 7200 IN NS ns4.321.google.com.
a.123.google.com. 7200 IN NS ns5.321.google.com.
a.123.google.com. 7200 IN NS ns6.321.google.com.
This goes on and on without coming closer to the nameserver that can actually answer the request for "a.123.google.com".
Back to my question:
Are horizontal referrals generally not allowed or is only this specific case a BAD horizontal referral?