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ccna 200-301 free training.A denial of service attack sends a large number of requests over a network or the Internet, and these excess requests prevent the target device from operating in an optimal state. As a result, the attacked device becomes unavailable for legitimate access and use. By executing malicious programs or a combination of malicious programs, DoS attacks slow down or crash applications and processes.1.3.1.2 Types of Reconnaissance AttacksReconnaissance, also known as information gathering, occurs in most cases prior to an access attack or DoS attack. In a reconnaissance attack, a malicious intruder typically begins with a full ping scan of the target network to determine which IP addresses are active. The intruder then determines which services or ports are available on the surviving IP addresses. Nmap is the most popular application for port scanning. Based on the port information obtained, the intruder queries the port to identify the type and version of the application and operating system running on the target host. In many cases, intruders look for vulnerable services to exploit when the likelihood of being caught is low.Reconnaissance attacks use a variety of tools to gain access to the network:.packet sniffers (packetsniffer).ping scans (pingsweep).port scanning (portscan). Internetinformationquery1.3.1.3 Packet SnifferA packet sniffer is a software application that uses a promiscuous-mode network adapter to capture all network packets passing through a LAN. In promiscuous mode, the network adapter sends all incoming packets to an application for processing. Some network applications distribute network packets in unencrypted plaintext. Since network packets are not encrypted, any application that can get them from the network can understand and process them.