detect blocks that self-redirect

respodns/dns.py

@@ -71,6 +71,11 @@ def process_result(res, ip, check, opts: Options):
     elif check.kind.startswith("bad"):
         reason = "okay" if "NXDOMAIN" in res else "redirect"
 
+    elif any(r == ip for r in res):
+        # server returned its own IP, must be a block, unless
+        # one of our checks actually contains a domain that also hosts a DNS.
+        reason = "block"
+
     elif any(is_bogon(r) or is_block_target(r) for r in res):
         reason = "block"