31 Days Before Your CCNA Exam

272 31 Days Before Your CCNA Exam■Access attacks: Entering or accessing systems by running a hack, script, or tool that exploitsa known vulnerability of the system or application being attacked. Common access attacksinclude the following:— Password attacks: Password attacks usually refer to repeated attempts to log in to ashared resource, such as a server or router, to identify a user account, password, or both.These repeated attempts are called dictionary attacks or brute-force attacks.— Trust exploitation: The process of compromising a trusted host and then using it tostage attacks on other hosts in a network.— Port redirection: A type of trust exploitation attack that uses a compromised host topass traffic through a firewall that would otherwise be blocked.— Man-in-the-Middle attacks: An attack carried out by persons who manage to positionthemselves between two legitimate hosts. If attackers manage to get into a strategic position,they can steal information, hijack an ongoing session to gain access to private networkresources, conduct denial-of-service attacks, corrupt transmitted data, or introducenew information into network sessions.■Denial-of-service (DoS) attacks: DoS attacks involve rendering a system unavailable byphysically disconnecting a system, crashing the system, or slowing it down to the point that itis unusable. Some examples of DoS attacks include the following:— Ping-of-Death attacks: Sending ping packets that are much larger than expected, whichmay crash older network systems.— SYN Flood attacks: Sending thousands of requests for a TCP connection (SYN bit isset) to a targeted server. The server leaves the connection open, waiting for an acknowledgementfrom the attacker, which never comes.— Distributed DoS (DDoS) attacks: Similar to DoS, but with hundreds or thousands ofattack points that attempt to overwhelm a target.■Malicious code attacks: Malicious software can be inserted onto a host to damage or corrupta system; replicate itself; or deny access to networks, systems, or services. Common namesfor this type of software are worms, viruses, and Trojan horses.— Worm: A worm executes code and installs copies of itself in the memory of the infectedcomputer, which can, in turn, infect other hosts.— Virus: A virus is malicious software that is attached to another program to execute aparticular unwanted function on a workstation. A virus normally requires a deliver mechanism,such as a zip file or some other executable file attached to an email. The key elementthat distinguishes a computer worm from a computer virus is that human interactionis required to facilitate the spread of a virus.— Trojan horse: Differs from a worm or virus only in that the entire application is writtento look like something else, when in fact it is an attack tool.