![]() ![]() When ICMP ping sweeps fail to discover hosts, other protocols can be used for the same purpose, such as TCP SYN or ACK segments, UDP datagrams sent to closed ports, etc.Īn adversary uses TCP SYN packets as a means towards host discovery. An adversary can cycle through various types of ICMP messages to determine if holes exist in the firewall configuration. To this end, virtually any type of ICMP message, as defined by RFC 792 is useful. It is important to recognize the key security goal of the adversary is to discover if an IP address is alive, or has a responsive host. Various other methods of performing ping sweeps have developed as a result. Most networks filter ingress ICMP Type 8 messages for security reasons. Other scanning utilities have been created that make ICMP ping sweeps easier to perform. While the Ping utility is useful for small-scale host discovery, it was not designed for rapid or efficient host discovery over large network blocks. Performing this operation for a range of hosts on the network is known as a 'Ping Sweep'. ![]() Ping, as commonly implemented, allows a user to test for alive hosts, measure round-trip time, and measure the percentage of packet loss. This type of exchange is usually referred to as a 'Ping' due to the Ping utility present in almost all operating systems. If the request is not blocked by a firewall or ACL, the target host will respond with an ICMP Type 0 Echo Reply datagram. ![]() An adversary sends out an ICMP Type 8 Echo Request, commonly known as a 'Ping', in order to determine if a target system is responsive. ![]()
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