A Study On Various Defense Mechanisms Against DDoS Attacks - IJSER

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International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-55181078A Study on Various Defense Mechanisms AgainstDDoS AttacksUjwal Sadhu, Anil Kumar Kotagadda Vijaya, Krishna Seth, Md.Tauseef Riasat, Mirza Hasan andOmar AbuzaghlehDepartment of Computer Science and Electrical Engineering,University of Bridgeport, Bridgeport, CT, 06604.Abstract—Distributed Denial of service (DDOS) attack is one of the biggest security threat to the Internet. This research paper attempts tostudy the DDOS attacks and its main types. The study will provide good knowledge to try for the defense measures for these attacks. Thenetwork is always vulnerable to this type of attack even after providing the security measures. This study will also focus on the ways todetect a DDOS attack and thus, start the processes to defense these attacks. The main objective is to understand the DDOS attacks andto find the security measures.Keywords— DDoS, Intrusion detection, preventive measures of DDoS, defense mechanisms, defense models, game theory, applicationmodel defense, new enhanced model.—————————— ——————————1. INTRODUCTIONTIJSERHE usage of Internet has been growing enormously.All the services which were, previously, a singlesystem are being transformed to multi user system.Even the most basic needs are performed on the internet.The purpose of the internet has shifted fromcommunication to computing. Hence, the dependency onInternet has increased drastically. The computing side ofthe internet has enabled the user to perform many services.A huge loss is incurred if there is an interruption to theseservices. This urges the need to protect the network morethan ever.One of the Security issues is caused by like Distributeddenial of service attack. This is one among the majorproblems faced by the internet users and the method todefend these attacks is very difficult. The result of theattack may be altering data through remote access ordamage the systems causing data loss. Nevertheless thedamage caused by these attacks on the internet causes ahuge loss.In this type of attack multiple hosts flood (sending tomany packets) the victim to cause the DOS. As the networktraffic to the server increases it causes the service denial forthe users. If this process takes its threshold, it is impossibleto be stopped. The result of the attack might beunauthorised access resulting in the data altering.Furthermore, worse than this is if the server is damageddue to the attack[1].So the objective of this paper is to study DDOS attacksclosely by understanding the way it exploits. We evenstudy the process which makes the system vulnerable, inan effort to avoid such errors. We also look at the process ofdetecting a system under attack, as well as exploring thepreventive measures.The need for this problem is to look at many aspects ofthe network to find out the root cause. This study aims toprovide knowledge on security measures that are to betaken or even more to improve the security issues[2].The past attacks on internet has caused substantialdamage to industries that rely on the internet. Attacks onMastercard.com, PayPal, Visa.com. has caused severedamages to prominent banks like Fifth Third Bank, BB&T,Wells Fargo, Citigroup, and HSBC, Capital One , PNC, U.S.Bancorp, Bank of America. There is a hacktivist groupcalled “Izz ad-Din al-Qassam Cyber Fighters” who hadbeen attacking the major banking websites. One of thebiggest attack is on the Cyber bunker with a record trafficof 300Gbps.[3]The target of the Dos attack is not only confined to acertain domain (like banking), because there are manyincidents which have encountered this situation.DoS attacks generally initiates by entering into the peersystems which causes the DDoS attacks. The (CERTComputer Emergency Response Team) CoordinationCenter (CERT/CC) has been maintaining overall statisticson Internet attacks since its inception more than 15 yearsago, and provide a general view of the trends.Fig. 1 gives the number of attacks reported to theCERT/CC from 1993 through 2003. It shows a massiveincrease over the past 11 years. It demonstrates that theimmense use of internet and communication medium isproportional to the DDoS attacks. The more usage ofinternet and data, the more chances are there of the attacks.As the incidents have been rising since the last decade, wecannot expect the end of these attacks in the comingfuture.[4]IJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-55181079Total Incidents 03Fig1: Incidents reported to the CERT/CC2. RELATED WORKAccording to the research paper on Distributed Denialof Service Attacks by lau, Stuart, Smith and Ljiljana. Theyhave characterised the DDoS attacks in four types.[5] Flooding a network hence stop the network traffic Disrupt connections between system to stop accessto service Deny a specific user from accessing server Deny service to a particular system or userAfter studying these attacks, they came to conclusion bybreaking down the process of attack into four steps. Firstly,victim receives a brunt attack. Then victim has to deal withthe daemon agents which are the programs that conductsthe attack. They are deployed from the host. To complete it,they have to access the host. The next step is to control themaster program which coordinates the process of attack.Then finally the hacker or attacker uses this program todirect the attack.This attack starts by sending an execute message tocontrol master program which upon receiving thecommand, activates the daemons to attacks. Thesedaemons then start the attack. All this process requires theattacker to infiltrate all the systems in the network makingit a difficult process. So the attacker must know thetopology of the network and the vulnerabilities which canbe used during the attack.The research also mentions about the defencemechanisms which can be implemented. Although these donot fully defend the attacks, but there are few securitymeasures to follow. Disabling IP Broadcasts, filteringrouters, disabling the unused services and performingintrusion detection are few mentioned mechanisms to belooked at.They have tried to simulate the attack to check the bestrouting algorithm and filed a report which read that almostall the routing algorithms failed to provide the bandwidthto the user during the attack, except for class based queuingalgorithm. Hence, they have concluded that the results dueto simulation show that protection against these attacks canbe achieved if the queuing algorithms are implemented.According to the research done by Yoohwan Kim, et. al.;the DDoS defense scheme were made familiar. Theseschemes deny the packets that are based on statisticalprocessing but supports online automated attack. Anotherresearch done by Jie Yu, Zhoujun Li, et. al. moreprominently focus on the attacks on application layer.[6]The network security faces many kinds of threats. Mostprominent among them are the DOS attacks. The securityof a computer is tested only if its data transfer reliability ismaintained. Basically, much of the network system isIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-5518vulnerable to Denial of service attacks. They can easilycrack through the application and the network layer of thenetwork model.The application layer is defenceless to the HTTPflooding. There is a huge flux of GET requests which startattacking the servers at an alarming rate, ultimately suckingall the image files from the server. It also results in firingmultiple queries one after the other, often leading to aserver jam. On the other side, the security measures of thenetwork layer are exposed when its important entities likeSYN, UDP and ICMP are flooded.[7]Many a times, the links or the websites are inaccessibleby the users. This may happen because they are attacked byWeb ServerAttackGenerationDerived parameters1080the Dos attacks. To counter it, a normal profile is createdwith the help of the characteristics and the behavior itshows to access the website. This helps in identifying thenormal user and the attacker. But while accessing awebsite, if the webpage takes more time to load up ascompared to the user to understand its content, it isconspicuous that there is an application layer Dos attack.[8]In here, the enhanced SVM plays an important role toprevent and detect the attack. ESVM, which has its stringkernels, identify the profile of a normal user to that of anattacker traffic and encounter the incursion. The DoSattacks are prominently subject to the packet number. Theframework specification of EVSM is also based on thepacket number only, thus proving its tingModel fileClassificationResultESVMTrainingFilter requestKernelLin earP Fig.Radial basisString2Weight valuesFig. 2 Attack classification system3. DEFENSE MEASURES3.1 DDoS Defense MechanismWhen DDoS flooding attack happens there is no other waybut disconnecting the sufferer from the network and fixingthe problem manually to get rid of the attack [1]. So adefense mechanism is very important to keep the systemout of danger from DDoS attack. In this paper we haveclassified two types of DDoS flooding attacks so we haveworked on the defense mechanism for those two DDoSflooding attack. These attacks are:12DDoS flooding attacks at Network/transport –levelDDoS flooding attack at Application-levelAccording to these attacks we have classified the defensemechanism into various criterions. First criterion: This classification is based on theprinciple that the defense mechanism works according to the location in which it is deployed. Ithas four categories:1. Destination based2. Source based3. Hybrid4. Network basedSecond criterion: The principle for classification isthe point of time when the DDoS defensemechanism must response to a possible DDoSflood attack [2]. These are:1. Before the attack2. During the attack3. after the attack3.1.1 Source based mechanism:In this mechanism preventing DDoS flooding attacksare done by deploying the defense mechanism near thesource [3].IJSER 2015http://www.ijser.org Advantages:

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-5518When the attack starts it can detect from thesource and respond very quickly before thetraffic attack wastes a lot of resources [4]. Disadvantages:1.Sometimes it becomes difficult to tell apartbetween genuine and the attack traffic atthe source.2.Filtering the attack flows accurately can bedifficult because the sources are spreadamong different domains. Advantages:2.It needs reliable communication amongvarious spread components in order tocooperate.3.Because of the collaboration andcommunicationamongdistributedcomponents scattered all over the internetit has complexity and over heading.During the attack (Attack Detection):It is cheaper and easier than the other mechanismsto protect the system from DDoS attack becausethey are applied close to the destination hosts.The attack detection can be the next step after theattack prevention process. It can be deployed atsources, intermediate networks, destinations or acombination of them. Disadvantages:Victims may get affected before the detection of theattack because it cannot perfectly detected tocounter the attack before it reaches the victims andcauses the damage to resources.After the attack (attack source identificationand response):IJSERBlocking the attack traffic and identify the attackers orsources of attack is the main responsibility of this typeof defense system which is placed after a DDoS attackhas detected.3.1.3 Network based mechanism:These mechanisms are implemented inside of a networkor mainly on the routers of the ASs. [10]This mechanism can detect and respond to theattack traffic at the middle networks closer to thesource. Disadvantages:2.There are lacking in incentives for theservice providers to cooperate.The time of the launching stage of the DDoS attack isthe best time to stop it. So a prevention system can bedesigned at the attack sources, midway networks,destinations or a combination of them.In this system the defense mechanism is applied at thedestination of the attack.1.1.Before the attack(Attack Prevention):3.1.2 Destination based mechanism: Advantages:1081The lack of adequate aggregated trafficdestined for the victims can createdifficulties for these mechanisms to detectattack.On the routers it has high storage andprocessing over-head.3.1.4 Hybrid mechanism:It is a cooperation based mechanism between serversand users to spot and react to the attacks [10]. Advantages:Classification by activity1.Intrusion PreventionThere are some DDoS defense mechanism which try toprevent systems from attackers.Applying globally coordinated filters: Ingress filteringwhich is proposed by Ferguson and Senie, it is amechanism to drop traffic with IP addresses where domainprefix connected router doesn’t match. It is an outboundfilter. This filters shows assigned IP address space leavesthe network. This filter does not help to save resourcehostage domain.Disabling unused service: For unused service, the networkservice should be disabled for prevent attacks.1.More strong against DDoS attacks.2.It has good amount of resources at variouslevels to deal with DDoS attack. Disadvantages:3.2 Classification of DDoS Defense mechanism:According to different criteria there are two classification ofDDoS defense mechanism. The DDoS defense mechanismdepends on the two classifications which are activitydeployed and location deployment.Applying security patches: The latest security patches forthe bugs should be updated by the host computer. Latestavailable technique should be used for preventing DDoSattacks.IJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-5518Changing IP address: For preventing local DDoS attacks,we can apply invalidation to the victim computer IPaddress with new one so that the edge router will dropattacking packet.Disabling IP Broadcasts: For attacks like ICMP flood,smurf attack, host computer cannot be used by disabling IPbroadcast.2.Intrusion DetectionBy recognizing anomalies in system, intrusion detectionsystem detect DDoS attacks.Anomaly detection:Anomaly detection system depends on detecting systembehavior which are abnormal comparing to other standardnetwork.Misuse detection:This detection system observes the well-defined pattern ofknown exploitation and then search for occurrences of thatpattern.3.1082According to the deployment mechanism, DDoS attackdefense mechanism are divided into different categories:Victim-Network Mechanisms: Most of the combatingDDoS attacking system are designed to work on the victimside. Resource accounting, protocol security mechanism areexamples of victim network mechanism.Intermediate-Network Mechanisms: The attack can behandles easily when the intermediate network mechanismare effective. Traceback and pushback are the example ofthis mechanism.Source Network Mechanisms: Before entering the internetcore, this mechanism in the source network can stop attackflows from various sources.3.3 Defense Mechanism ALPi: A DDoS DefenseSystem for High-Speed Networks:To counter the DDoS attacks, we are introducing theconcept ‘Packet Score’ that identifies the DDoS attack,separates them from the real ones by using packet scoringand abandons the low scoring ones.But sometimes, the complexity and performance take itstoll over the working of Packet scoring. At this point oftime, ALPi comes to rescue. Also the score computation ismitigated with the help of leaky-bucket overflow controlscheme, which also increases the speed of the process withsubstantial standards[13].IJSERIntrusion Response.IP Traceback: For achieving path characterization, it tracesthe attack back to their origin so that the true identity of theattacker can be found.ICMP Traceback: In this traceback mechanism, using lowprobability every router samples the forward packets andthen send ICMP traceback message toward destinationA link-testing traceback: this technique is proposed byBurch and Cheswick [12]. By flooding with large burst oftraffic, this system infers the attack path.CenterTrack [ll] this system is proposed by Stone. Thissystem creates an overlay network of IP tunnels byconnecting all edge routers to central tracking routers.Hash-based IP traceback has been proposed by Snoeren, etal. Source path isolation engine (SPIE) generates audit trailsof traffic and then trace origin of single IP addressIntrusion ToleranceIntrusion tolerance can be classified into two parts. Faulttolerance and quality of Service.The process of fault tolerance is to duplicate the networkservice and diversify its access point so the network cancontinue offerings its service when flooding traffic occurredin the network link [11].Quality of service (QoS) explainsthe assurance of ability of network to deliver predictableoutcome for different types of application.Because of the increasing traffic, it is important toidentify the any attack quickly, to prevent the obstructionof data flow. These problems are overcome by attributevalue-variation scoring scheme and enhanced controltheoretic packet discarding method.The collaboration of these two methods excessivelyincreases the ability to recognize the attack and alsoreduces the memory allocation. These qualities make ALPi,an immensely reliable DDoS defense system[9].Packet Scoring:Packet scoring [25] has been used by various networkappliances like Stealthwatch and Webscreen [23] and [24].A defense system must be able to handle and confront withany type of attack. It should also be able to provideappropriate solutions to the attack. These qualities areprominently included in packet scoring. It is a very efficientdefense system, which has the ability to detect and blockthe first-timer attacks. It applies the packet-scoringapproach to counter the attacks.Every incoming packet which arrives, is given a specificscore. These scores are given depending on the TCP/Ipprotocols. If any of the packet has a score that exceeds tion by Deployment LocationIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-55181083IJSERFig. 3. Deployment of 3D-Rs and DCSs to tackle end-point DDoS attacksII. CLP based PacketScore structure:In this scheme, some routers (3D-Rs) [21] are introducedin the structure, which performs the main function ofdetection of attacks, separating them from the legitimateones and discarding them. The 3D-Rs are implemented onthe control servers of the DDoS.Server is able to deal the control messages with the routers,which is the reason why it is placed separately from thenormal data communication path. This structure keeps itsafe from the attack. Moreover, the terminals within theDCS [22] are segregated in a certain domain.Now, with a suitable environment to work in,PacketScore plays its crucial role. It uses CLP to sum up thescore (tally) of all the packets which pass through the CLPbased scheme. It is processed in a triple phase:i)Evidence to support the confirmation of any attackwhich is based on certain protocols including the detectionand identification of victim. The DCS forwards this firstreport to the 3D routers. by supervising all the importanttraffic statistics of every protected target i.e. number ofactive flows, bits/sec, packets/sec and flow rate of newarriving packets. All this while, per-target states are kept tothe lowest.ii) A score is allotted to every packet to distinguishbetween the original and the attacking ones. Each of thepacket has a traffic profile which is nominal and/orcurrent. When these two are compared, a score isgenerated, then computed by CLP and saved in the shapeof scorebooks. This results in the increase of the relativefrequency of the attacker in the current profile. As a result,the attribute value shared by attacking packet will be givena lower score.iii) Dynamic threshold is used to compares the scoreof the packet for removing the low score packets. Dynamicthreshold, is adjusted according to:Fig.IJSER 2015http://www.ijser.org1.The score distribution of all suspiciouspackets and2.The congestion level of the victim.4summarizesthePacketScorescheme.

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-55181084Fig. 4. Simple diagram of PacketScore scheme𝑑𝑞 𝑎𝑝𝑑𝑎3.4 Attack vs defense modelThere is a need for finding the best process for DDoSdefence mechanism. This is done by comparing themechanisms on a scale. Here there is a need formeasurement.Here p is the attack and q is the defence. ‘a’ is the rate atwhich the threat is minimised by the defence. ‘b’ is the rateat which the attack damages the defence.The defiance mechanism’s performance can bemeasured by genuine traffic rate passed (GTRP) and attacktraffic rate passed (ATRP).Here we assume that a,b are independent of thestrengths of attack and defence. They are also constant overtime. At t 0GTRP ATRP IJSER𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑔𝑒𝑛𝑢𝑖𝑛𝑒 𝑡𝑟𝑎𝑓𝑓𝑖𝑐 𝑟𝑎𝑡𝑒 𝑝𝑎𝑠𝑠𝑒𝑑 𝑎𝑝𝑑𝑞 𝑎𝑞𝑑𝑝𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑔𝑒𝑛𝑢𝑖𝑛𝑒 �� 𝑜𝑓 𝑎𝑡𝑡𝑎𝑐𝑘 𝑡𝑟𝑎𝑓𝑓𝑖𝑐 𝑟𝑎𝑡𝑒 𝑝𝑎𝑠𝑠𝑒𝑑𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑎𝑡𝑡𝑎𝑐𝑘 𝑝𝑎𝑐𝑘𝑒𝑡𝑠Now, we measure the performance by dividing GTRPover ATRP as mentioned in the below formulae.Performance 𝐺𝑇𝑅𝑃(2)(3) 𝑎𝑞𝑑𝑞 𝑑𝑝𝑎𝑝 (4)If we integrate we get𝑎(𝑞 2 𝑞0 2 ) 𝑎(𝑝2 𝑝0 2 ) (5)As p(0) p0 and q(0) q0 at t 0 (6)𝐴𝑇𝑅𝑃If the result is then the system is a perfect defence asATRP is 0. On the contrary if the result is 0 then defencesystem is the worst case as the GTRP is 0.Lanchester’s square law states :So if we are to find the best defence mechanism thanmeans the performance should me higher.Hence𝐾 𝑎𝑞0 2 𝑎𝑝0 2 (7)When𝑎𝑞 2 𝑎𝑝2 𝐾 (8)AssumptionsWe have two non-negative functions of time continuousdifferentiable assume them as f(t), g(t). The minimum valueof the functions are 0.The probability of damage caused by the attack isproportional to the strength of the defence. This can bemathematically expressed as[16]:𝑑𝑝 𝑎𝑞𝑑𝑎(1)K 0 that means the graph is hyperbolaK 0 that means the hyperbola intersects x axis thisis when attack winsK 0 that means the hyperbola intersects y axis thisis when defence winsK 0 that means the graph is a straight lineANALYSISIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-5518As stated above when the K is greater than 0 that meansthe attack is successfully defended. Hence at this point theequation is𝑞0𝑎( )2 𝑝0𝑎(9)As a,b are constant, increase in twice of the defencestrength would result the attacker to improve his strength 4times the original. Hence we can assume that if the systemis more secure the attacker has to expand his attack morethan the needed.The equations (1) and (2) solving by (6) gives thefollowing𝑎𝑞(𝑎) 𝑞0 cos 𝑎𝑎𝑎 𝑝0 𝑠𝑖𝑛 𝑎𝑎𝑎𝑎(10)𝑎𝑝(𝑎) 𝑝0 cos 𝑎𝑎𝑎 𝑞0 𝑠𝑖𝑛 𝑎𝑎𝑎𝑎(11)The equation (10) is written as:𝑝0 𝑎𝑞(𝑎) 𝑞0 cos 𝑎𝑎𝑎 𝑠𝑖𝑛 𝑎𝑎𝑎𝑞0𝑞0 𝑎SSFNet is the simulator used to test the defenseperformance. TFN2K is embedded into the simulator forthe virtual attack. The defense is tested at 3 differentinternet speeds 100KBps, 200KBps, 300KBps. The graph ismade according to the outputs. The inputs are taken formdatasets of server at ipv4.20040120 on 09/Jan/2004[18]. Thegraph proves that the genuine traffic can be more and theattack traffic passes less. Hence this system is better thanthe current systems.3.5 A Application layer level defense mechanismThe DDoS attacks are conducted at all the transport,application and network level. The reason for most attacksto be targeted on application layer is that the defence toolshave low control over the transport layer. Hence theprotection in the application layer is less as the attackerhave to overcome only few security levels when comparedto the other layers.The DDoS attacks can be classified based on theirdetection by the defence system minor, transitional,modern [17].(12)Minor attacks are the majority of the attacks which arecurrently on the internet. The Http request for attacks doneby the bots send either one or a specified limited number ofrequests to the victim. Based on these HTTP requestimplementation we can further subdivide them into 3types. The HTTP requests containing an unknown useragent strings or a known malicious strings (type1), a stringwhich is named as a spoofed crawler string (type 2) andnamed spoofed web browser string (type3).IJSERAccording to the above equation the defence strength𝑎𝑎depends on the 2 values and 𝑎𝑎𝑎. Here represents𝑏𝑏the ratio of attack to the defence and their effectiveness. 𝑎𝑎 represents the intensity of the defence, attack. 𝑎𝑎 tellsthe time taken by either of the processes to end.Achievements1085This theoretical model hence is accustomed to know theattack and defense strength as well as their relationshipwith one other.The procedure from which the output is producedthrough the input is recurring for every attack. Hence itpredicts the output if attack is same.SimulationTransitional attacks are the attacks better than the minorattacks. A random predefined sequence of the pages in awebsites are requested by the bots which are used in thewebsites. This makes the traffic look genuine. To detectsuch type we need to compare the attack with genuineModern attacks the request sent is made to look like it isgenerated through a genuine web browser for a webpages.Minor attacks can be detected through simple packet bypacket inspection.Transitional attacks are detected through the advancedmethods but the defending them is a lot hard whencompared to the minor.Modern attacks are the high end attacks detectedthrough high intelligent algorithms of data mining.The Application-Layer DDoS DefenseFig3: Experimental valuesThe system consists of three stages of detectionmechanism for all the 3 types of attacks. The stage onedetects the minor type, transitional in stage 2 and themodern in stage 3 .This is mainly based on the suspiciousdetection hence may be few cases of human may beIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-5518considered as the suspicious. These are resolved byCAPTCHA tests or similar tests.Stage 1 detects the minor attacks. AS discussed theminor attacks are classified into 3 which have a detectionmechanism of their own. The type1 attacks are identified ifthey are from unknown string or which are alreadyidentified as the malicious. The type2 attacks are identifiedby checking if the IP address of the bot matches to thedomain of the bot’s string from the reverse engineeringDNS lookup. The type3 attacks are identified if thebehaviour is like a true browser.Stage 2 detects the transitional attacks. These attacks aredetected by verifying the sequence of browsing in achronological order (BSC). Therefore the sequence is firsttaken from each session and then passed to stage 1. Thenalgorithms like ILOF, COD and DStream [20] are applied toidentify the contents of the sequence and know the new orchanged sequence [19]. The algorithm is implementedusing the metric of the subsequence that is longest commonwhich is normalized in length (LCSLN):𝐿𝐶𝑆𝐿𝑁 𝐵𝑆𝐶𝑖 , 𝐵𝑆𝐶𝑗 1 1086If the sequence is marked suspicious it is not sent tostage 3. If CAPTCHA test fails the access to website isblockedStage 3 detects modern attacks. These are performed byinspecting the website and generating the sequence ofrequest which are seemed to be human requests. Anunderstanding of how a human browses is to be known inorder to detect such attack an example of a characteristicfeature is page viewing time. The content of the website,the content and visitor rate relation, time taken by the userto navigate from a page based on the content of the pageare few parameters that are to be considered. Systemcalculates the web session time then algorithms areimplemented to know the system determined time. If theuser time exceeds the systems time then the access to site isblocked.During the attacks 92% of the attacks are identified asmalicious. Also 27% of the human users are identified asmalicious who are provided with CAPTCHA to provehuman users. 𝐿𝐶𝑆 𝐵𝑆𝐶𝑖 ,𝐵𝑆𝐶𝑗 IJSER 𝐵𝑆𝐶𝑖 𝐵𝑆𝐶𝑗 Fig4: Machanism of DDoS new mechanism3.6 Game model Theory:As the use of internet and network technologies havebeen increased tremendously in the day to day lifeirrespective of fields, along with that there are largeramount of threats and malicious attacks being equallytaking place over the network which is causing a hugeeconomic loss. Since the attacks are not targeted only forIJSER 2015http://www.ijser.org

International Journal of Scientific & Engineering Research, Volume 6, Issue 5, May-2015ISSN 2229-5518common servers it has become difficult to analyze andprevent these attacks. To overcome these attacks, manymechanisms have been designed through the defensemechanisms. As the defense mechanisms deal withanalyzing specific pattern of attacks and prevention ofthese similar attacks, the other common attacks have beenleft back. So, this paper not only elaborates defensemechanisms but also the other common DDoS attacks andtheir prevention. This paper is split into different sectionsand each section will discuss different DDoS attacks andtheir prevention.Sec-1: Firstly we shall start with defense mechanismprevention techniques. The methods of defensemechanisms we propose are based on various methods ofcongestion control. The aim of this paper is to presentDDoS defense mechanism in an effective and evaluatedmanner using game-theoretical methodology. A fullstr

detect a DDOS attack and thus, start the processes to defense these attacks. The main objective is to understand the DDOS attacks and to find the security measures. Keywords— DDoS, Intrusion detection, preventive measures of DDoS, defense mechanisms, defense models, game theory, application model defense, new enhanced model.

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Defense Logistics Agency (DLA) is a defense agency under the U.S. Department of Defense (DoD) . The DLA Director reports to the Under Secretary of Defense for Acquisition, Technology and Logistics through the Deputy Under Secretary of Defense for Logistics and Materiel Readiness. DLA provides worldwide logistics support for