Denial Of Service Attack Computer Science Essay

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Denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) will attempt to make a computer resource, be it a printer or a website, unavailable to its users. It will concerted effort of a person to prevent an internet site for functioning efficiently. There are three main ways a DoS attack happens overload computational resources like CPU time or CPU cycles, disruption of configuration information and unavailability to physical network components.

http://upload.wikimedia.org/wikipedia/commons/thumb/3/3f/Stachledraht_DDos_Attack.svg/220px-Stachledraht_DDos_Attack.svg.png

From above shown diagram states how ddos attack happens.

Syn flood attack is a DoS attack in which syn flood attack, client requests a connection by sending a syn message to server. then server acknowledges this request by sending syn-ack back to the same client and finally client responds with an syn -ack and connection is made . traditional tcp three way handshake connection is established

3. Litrature review

The internet today is driven by machines that communicate using services layered on top of the tcp/ip protocols it includes ftp,http,and ssh .Tcp services are often susceptible to various types of DOS(denial of services )attacks from external hosts on the network, one such attack is known as syn flood

In syn flood attack client requests a connection by sending a syn message to server. Then server acknowledges this request by sending syn-ack back to the same client and finally client responds with an syn -ack and connection is made. Traditional tcp 3 way handshake connection is established syn flood attack works if server allocates resources after receiving a syn, but before it has to receive ack(acknowledgment) which it never gets.

There are two ways to find syn flood attack but both involve the server not to resaving ACK.

1. Malicious client can skip sending last ACK message.

2. Spoofing the source ip address in the syn

http://upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Tcp_normal.png/220px-Tcp_normal.png

A normal connection between a user and server. Three-way handshaking is correctly performed by seeing above diagram we say it

http://upload.wikimedia.org/wikipedia/commons/thumb/9/94/Tcp_synflood.png/220px-Tcp_synflood.png

The attacker sends several packets but does not send the "ack" back to the server. Hence the connections are half opened and absorbing server resources another user tries to connect but server refuses to open a connection it results to denial of service

For creating half-open connections is easily completed with ip spoofing. if the attacker system sends syn messages to the victim server system it will seems to be legitimate but in fact reference a client system that is to respond to the syn-ack message . And final ack message will be never sent to the server system. Half-opened connections do eventually expire as they have a time out hence this attack may not be successful. But the attacker can just send more requests for connection faster than the time out so as to exhaust the server's buffer for connections.

Though it doesn't usually affect the connections which are already established it may cause other problems. It has been seen in some cases that the victims system may be overwhelmed and crash or be turned not functional.

3.2Problem Area: As we have discussed the mechanism of SYN attack above in detail, this paper plans to solve the way to detect the attack through a network management tool.

4. Statement of findings

Successful condition monitoring is established on powerful and user friendly machine symptomatic software for data management and analysis. The various issues of the problem area can overcome using the Observer tool for this network server monitoring. The observer tool is cost effective reducing the cost of the network management. It also helps to monitor remote sites by saving the time and cost of the administrators. This is helpful for multi session remote monitoring. Observer suite is a network monitors and protocol analysis software used for the Microsoft, UNIX and for many wireless networks. This can quickly detect, solve and prevent network problems in more effective way. The Observer software contains huge variety of tools for advanced root analysis

Process of attack

The tool which has been used

I have mentioned the findings and given respective analysis in the next topic for a more structured approach

5. Analysis and discussion

Utilisation thermometer:

By using utilisation thermometer we can exactly find out the performance of a network it will show the utilisation percentage and the data transfer in MB/s so by that we can analyse the performance of the network. In the observer we can find this option by going into statistics Utilisation thermometer, the screen shot taken by me in shown below.utilisation thermometer2

Bandwidth utilisation:

Bandwidth utilisation is also another parameter which helps you to analyse the performance of the network this graph has bandwidth utilisation percentage in the y-axis and time in the x-axis which analyse the bandwidth utilisation percentage time to time. In the observer we find this from statistics Bandwidth utilisation and the screen cap is shown below.

 Packet capture: This packet capture is available in a graph which has PKTS/s in y-axis and time in the x-axis so that it will analyse the packets transfer per second in the network so it helps to analyse the total number of packets each interval a station receiving and transmitting. In the observer we can find this in capture packet capture and the screen cap is shown below

Packet capture2

Errors by station:

In the observer when you go to the statistics Errors by station a window opens and when you click start it will analysing the errors in the each station in the whole network, now you may ask what is the use if the errors increasing in the network automatically by errors performance of the network decreases, and the screen cap is shown

errors by station2

See in the graph we have CRC and the other error analysis.

Top talkers:

Top talkers is available in a graph which shows the station wise bandwidth utilisation and the percentage of packets receiving and transmitting by each and every station, by this graph we can find out which stations are using the bandwidth much. In the observer we can find this by going into statistics Top talkers and click start to analyse and the screen is like

top talkers2

Vital signs:

Vital signs are also a graph which will help you to find out the error position in the network and here in this graph errors are shown in colours. Yellow indicate the network is idle green indicate errors are in threshold level and red indicate errors are above threshold level. In the observer we find this in statistics vital signs

vital signs2

Activity display:

Activity display is also a graph which shows you the three data's in a single graph it will analyse the utilisation%, broadcast% and multicast% and it shows the reading time and the average utilisation%

activity display2

The above shown screen is the activity display screen analyses three data's at a time. In the observer we find this by going to Statisticsactivity display.

Size distribution statistics:

Size distribution statistics is an analysis in which we can find out the packets transmitted, received and the total number of packets by each station can be analysed to analyse performance of each station in the network. In observer, Statistics Size distribution statistics

size distribtion statistics2

These are some of the useful parameters that can analyse the performance of the network by using observer.

Observer as a security analysis:

Some of the options that are provided by the observer which helps in security analysis are

Alarm settings

History observing using SNMP MIB editor.

Detecting other station configurations using SNMB MIB walker.

Finding out WEP.

Alarm settings:

Alarm settings are available in the observer and alarms can be fixed too many options in the observer we can keep alarms in decreasing performance, errors increasing for everything alarms can be fixed for security purposes.

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