Identifying network loops is disclosed including determining a first data packet having a time to live (TTL) that at least meets a first condition, the first data packet having a destination internet protocol (IP) address; within a time period after the determining of the first data packet, identifying a plurality of second data packets that are to be transmitted to the destination IP address; and determining whether a network loop exists for the destination IP address based on TTLs of the plurality of second data packets.