An Internet “linking agreement” has spawned a $1 million federal lawsuit in which CDnow Inc., an online music seller, claims that Lycos, a popular search engine, broke its promise to run its ads and to reject all ads from its competitors.

David A. Capozzi, CDnow’s general counsel, filed the suit against Waltham, Mass.-based Lycos and its subsidiary, Tripod Inc., a Web-services company.