DNAME-DNAME loop test case is not a loop

Hi,

I was checking the behavior of Knot and BIND when there is an infinite DNAME recursion as in the following zone file:

campus.edu.	500 SOA	ns1.campus.edu. root.campus.edu. 3 86400 7200 604800 300
campus.edu.	500 NS	ns1.outside.edu.
d.campus.edu.	500 DNAME	f.d.campus.edu.

For the query <a.f.d.campus.edu, A>, the response returned by BIND was:

          "opcode QUERY",
          "rcode NOERROR",
          "flags QR AA RA",
          ";QUESTION",
          "a.f.d.campus.edu. IN A",
          ";ANSWER",
          "d.campus.edu. 500 IN DNAME f.d.campus.edu.",
          "a.f.d.campus.edu. 500 IN CNAME a.f.f.d.campus.edu.",
          "a.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.d.campus.edu.",
          "a.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",
          "a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu. 500 IN CNAME a.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.f.d.campus.edu.",

whereas the response from Knot was:

          "opcode QUERY",
          "rcode NOERROR",
          "flags QR AA",
          ";QUESTION",
          "a.f.d.campus.edu. IN A",
          ";ANSWER",
          "d.campus.edu. 500 IN DNAME f.d.campus.edu.",
          "a.f.d.campus.edu. 500 IN CNAME a.f.f.d.campus.edu.",
          ";AUTHORITY",
          ";ADDITIONAL"

I checked with NSD implementation too, and they did what Knot did, and the logs in NSD mentioned DNAME processing stopped due to loop, qname a.f.d.campus.edu.

Its harder to say which one is the correct behavior as the zone file is not proper. I found out that Knot has a test-suite comparing its answers with BIND, and there is a mention of the DNAME-DNAME-Loop case. There is a minor error in the input query in this test case due to which the above difference did not come out and the test passed. The relevant records from the flags.zone are:

dname	DNAME	dname-tree
f.dname-tree	DNAME	dname-tree
dname-tree	A	1.2.3.4

The test case is <f.dname.flags., A>. The first DNAME applies initially and the query is changed to <f.dname-tree.flags., A> but after that, the next DNAME does not apply so there is no loop.