If this query is sent to either A.ISI.EDU or C.ISI.EDU, the reply would be:
+---------------------------------------------------+ Header | OPCODE=SQUERY, RESPONSE, AA | +---------------------------------------------------+ Question | QNAME=USC-ISIC.ARPA., QCLASS=IN, QTYPE=A | +---------------------------------------------------+ Answer | USC-ISIC.ARPA. 86400 IN CNAME C.ISI.EDU. | +---------------------------------------------------+ Authority | <empty> | +---------------------------------------------------+ Additional | <empty> | +---------------------------------------------------+
Because QTYPE=CNAME, the CNAME RR itself answers the query, and the name server doesn't attempt to look up anything for C.ISI.EDU. (Except possibly for the additional section.)