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7.4.2 Active Attacks >  Attacks by dropping packets - Pg. 151

CHAPTER 7 Security for Mobile Ad Hoc Networks 151 7.4.2. Active Attacks Due to lack of infrastructure and the vulner- ability of wireless links, the current routing protocols for MANETs allow launching of dif- ferent types of attacks. Compared with pas- sive attacks, malicious nodes running an active attack can actively participate to disrupt the nor- mal operation of network services. It interrupts the accurate execution of the routing protocol by modifying routing data, by fabricating false routing information, or by impersonating other nodes. Basically, active security attacks against ad hoc routing protocols can be classified into differ- ent groups as explained in [3]. We describe them below as given by the authors: a. Attacks by dropping packets b. Attacks using modification of protocol messages fields are transferred to the attacker node and he dis- cards all of them. (ii) Gray hole: The attacker is selective in drop- ping packets. In this case, the malicious node has the ability to switch its course of action from forwarding routing packets or discarding oth- ers. The decisions of its behavior depend on the intention of the attack. A node in the established routing topology selectively drops packet caus- ing network disruption which can be difficult to detect. Depending on the drop rate and type of data that is dropped, detecting of this type of attack is challenging. An overloaded node, through no fault of its own, might selectively drop packets, thus behaving like a Gray hole. · Attacks using modification of protocol messages. Current routing protocols assume a cooperative environment such that nodes do not alter the protocol fields of messages passed among nodes. Routing protocol packets carry