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When the attacker uses a proxy to connect to the destination, the proxy's source address will be recorded in the server logs instead of the actual source address of the attacker. In addition to this, the reasons for which attackers use proxy servers include: Q Attacker appears in a victim server's log files with a fake source address of the proxy rather than with the attacker's actual address 9 9 To remotely access intranets and other website resources that are normally off limits To interrupt all the requests sent by an attacker and transmit them to a third destination, hence victims will only be able to identify the proxy server address 9 To use multiple proxy servers for scanning and attacking, making it difficult for administrators to trace the real source of attack.

Use of Proxies for Attack Quite a number of proxies are intentionally open to easy access. Anonymous proxies hide the real IP address and sometimes other information from websites that the user visits. There are two types or anonymous proxies: One that can be used in the same way as the nonanonymous proxies and others that are web-based anonymizers.

Let's see how many different ways that attackers can use proxies to commit attacks on the target. Case 1: In the first case, the attacker performs attacks directly without using proxy. The attacker may be at risk to be traced out as the server logs may contain information about the IP address of the source. Case 2: The attacker uses the proxy to fetch the target application. In this case, the server log will show the IP address of the proxy instead of the attacker's IP address, thereby hiding his or. This will give the attacker the chance to be anonymous on the Internet.

Case 3: To become more anonymous on the Internet, the attacker may use the proxy chaining technique to fetch the target application. If he or she uses proxy chaining, then it is highly difficult to trace out his or her IP address. Proxy chaining is a technique of using more numbers of proxies to fetch the target. User requests a resource from the destination 2. Proxy client at the user's system connects to a proxy server and passes the request to proxy server 3. The proxy server strips the user's identification information and passes the request to next proxy server 4. This process is repeated by all the proxy servers in the chain 5.

At the end unencrypted request is passed to the web server.

Unknown rogue malware/trojans in my Windows 7 PC

Proxy C haining Proxy chaining helps you to become more anonymous on the Internet. Your anonymity on the Internet depends on the number of proxies used for fetching the target application. If you use a larger number of proxy servers, then you will become more anonymous on the Internet and vice versa. W hen the attacker first requests the proxy serverl, this proxy serverl in turn requests another proxy server2.

The proxy serverl strips the user's identification information and passes the request to the next proxy server. This may again request another proxy server, server3, and so on, up to target server, where finally the request is sent. Thus, it forms the chain of the proxy server to reach the destination server as shown in the following figure:. The socket connection diagram is an animated graphical history of all of the events that took place on the socket connection.

Dead Dead Dead It allows you to surf websites that are restricted or blocked by your government, organization, etc. Features: e 9 Q You can access the Internet from a restricted network through a proxy server gateway It hides your IP address It can work through a chain of proxy servers using different protocols It allows you to bypass firewalls and any access control mechanisms.

EXE 64 cxplore. Taiget Rule: Proxy Default: proxy. It also helps you to access various sites that have been blocked in the organization. It avoids all sorts of limitations imposed by sites. Features: 9 Q It hides your IP address It allows you to access restricted sites It has full support of password-protected servers.

Elite 30 B Dead Basic Anonymity j.. ProxySwitcher 0. To [ It hides your IP from being displayed in the server's log or mail headers. You can use Tor to prevent websites from tracking you on the Internet. You can also connect to news sites and instant messaging services when these sites are blocked by your network administrator. Tor makes it difficult to trace your Internet activity as it conceals a user's location or usage.

Provides anonymous communication over the Internet Ensures the privacy of both sender and recipient of a message Provides multiple layers of security to a message Encrypts and decrypts all data packets using public key encryption Uses cooperating proxy routers throughout the network The initiating onion router, called a "Tor client" determines the path of transmission.

Proxy Tools In addition to these proxy tools, there are many more proxy tools intended to allow users to surf the Internet anonymously. F rtt Proxy ana Privacy Toots - sun Tne w co F ree Proxy Servers Besides proxy tools discussed previously, you can find a number of free proxy sites available on the Internet that can help you to access restricted sites without revealing your IP address. Just type Free Proxy Servers in the Google search engine and you will get numerous proxy server websites. The HTTP protocol acts as wrapper for communication channels. It is a client-server-based application used to communicate through the HTTP protocol.

This software creates an HTTP tunnel between two machines, using a web proxy option. The attacker uses the client application of HTTP tunnel software installed on his or her system to communicate with other machines. The HTTP tunneling technique is used in network activities such as: 9 9 9 9 Streaming video and audio Remote procedure calls for network management For intrusion detection alerts Firewalls.

HTTP tunneling allows you to use the Internet despite having firewall restrictions such as blocking specific firewall ports to restrict specific protocol communication. The attacker may use this technique for the following reasons: 9 9 9 9 9 It assures the attacker that no one will monitor him or her while browsing It helps the attacker to bypass firewall restrictions It ensures secure browsing The attacker can hide his or her IP address from being trapped It assures that it is highly impossible for others to identify him or her online by sending specific protocol.

In this case, you can send your packets via HTTP protocol as shown in the following figure:.

It is like secure VPN software that allows you to access your Internet programs without being monitored by your work, school, or the government, and gives you an extra layer of protection against hackers, spyware, or ID theft. It can bypass any firewall. It is very secure software. Using this software does not allow others to monitor your Internet activities.

It hides your IP address; therefore, it does not allow tracing of your system. It allows you the unlimited transfer of data. It runs in your system tray acting as a SOCKS server, managing all data transmissions between the computer and the network. This forwards the local port to port 25 on certifiedhacker. It also helps you hide your IP address on the Internet; therefore, no one can trace or monitor you. The prerequisite of SSH tunneling is raised from the problems caused by the public IP address, the means for accessing computers from anywhere in the world.

The computers networked with the public IP address are universally accessible, so they could be attacked by anyone on the global Internet easily and can be victimized by attackers. An SSH tunnel is a link that proceeds traffic from an indiscriminate port on one machine to a remote machine through an intermediate machine. An SSH tunnel comprises an encrypted tunnel, so all your data is encrypted as it uses a secure shell to create the tunnel.

Creating a tunnel for a privately addressed machine needs to implement three basic steps and also requires three machines. The three requisite machines are: 9 9 9 Local machine An intermediate machine with a public IP address Target machine with a private address to which the connection must be established. You can create a tunnel as follows: 9 Start an SSH connection from local machine to the intermediate machine with public IP address.

This is called port acceleration or port forwarding. Now, when you connect to the local port, it will redirect the traffic to the remote machine. To secure communication between computers, SSH uses private and public encryption keys. The public encryption keys used by the SSH tunneling deed like the identifiers of the authorized computer.

On initiating an SSH connection, each machine exchanges public keys, but only the computer that has the matching private key can attain access to the remote computer applications and information and can read encrypted communications with the public key.

Additionally, OpenSSH provides secure tunneling capabilities and several authentication methods, and supports all SSH protocol versions. OpenSSH can be used to tunnel the traffic on local machine to a remote machine that you have an account on. This essentially forwards the local port to port 25 on certifiedhacker. Simply point your email client to use localhost as the SMTP server.

SSH Client includes powerful tunneling features including dynamic port forwarding through an integrated. IBO Applicati. B4Q Application Turn 0 1lor. The server provides you secure remote login capabilities to Windows workstations and servers. The Bitvise server even has the ability to encrypt the data during transmission so that no one can sniff your data during transmission. Name ntvterrnc. A n o n y m iz e rs J An anonymizer rem oves all the identifying inform ation from the user's computer while the user surfs the Internet J J Anonymizers make activity on the Internet untraceable Anonymizer tools allow you to bypass Internet censored websites.

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A nonym izers An anonymizer is an intermediate server placed in between the end user and web site that accesses the website on behalf of you, making your web surfing untraceable. An anonymizer eliminates all the identifying information IP address from your system while you are surfing the Internet, thereby ensuring privacy. Most anonymizers can anonymize the web http : , file transfer protocol ftp : , and gopher go p her: Internet services. To visit a page anonymously, you can visit your preferred anonymizer site, and enter the name of the target website in the Anonymization field.

Alternately, you can set your browser home page to point to an anonymizer, so that every subsequent web access will be anonymized. Apart from this, you can choose to anonymously provide passwords and other information to sites that request you, without revealing any other information, such as your IP address. Crackers may configure an anonymizer as a permanent proxy server by making the site name the setting for the HTTP, FTP, Gopher, and other proxy options in their applications configuration menu, thereby cloaking their malicious activities. Ensures privacy: It protects your identity by making your web navigation activities untraceable.

Your privacy is maintained until and unless you disclose your personal information on the web by filling out forms, etc. Accesses government-restricted content: Most governments prevent their citizens from accessing certain websites or content in order to avoid them from accessing inappropriate information or sensitive information. But these people can access even these types of resources by an anonymizer located outside the country. Protect you from online attacks: Anonymizers protect you from all instances of online pharming attacks by routing all customer Internet traffic via the anonymizer's protected DNS servers.

Bypass IDS and firewall rules: Bypassing of firewalls is mostly done in organizations or schools by employees or students accessing websites they are not supposed to access. An anonymizer service gets around your organization's firewall by setting up a connection between your computer and the anonymizer service. By doing such, firewalls can see only the connection from you to anonymizer's web address. The anonymizer will then connect to Twitter or any website you wanted to access with the help of an Internet connection and sends the content back to you.

For your organization, it looks like your system is connected to an anonymizer's web address, but. Anonymizers, apart from protecting users' identities, can also attack the website and no one can actually detect where the attack came from. Types of A nonym izers An anonymizer is a service through which one can hide their identity when using certain services of the Internet.

It basically works by encrypting the data from your computer, so that is cannot be understood by Internet service providers or anyone who might try to access it. Since the information passes through several Internet computers, it becomes more cumbersome for anyone trying to track your information to establish the connection between you and anonymizer. Example: If you want to visit any web page you have to make a request. The request will first pass through A, B, and C Internet computers prior to going to the website.

Then after being opened, the page will be transferred back through C, B, and A and then to you. Disadvantage: Any multi-node network communications have some degree of risk at each node for compromising confidentiality. S in g le -p o in t A n o n y m iz e rs Single-point anonymizers first transfer your information through a website before. Advantage: IP address and related identifying information are protected by the arms-length communications. Bloggers and journalists in China are using a novel approach to bypass In tern et filters in their country - th ey w rite backwards or from right to left.

China is well known for its implementation of the "packet filtering" technique. To bypass Internet filters and dodge the censors, bloggers and journalists in China are writing the text backwards or from right to left. By doing so, though the content is still in human readable form, the text is successful in defeating web filtering software. Bloggers and journalists use vertical text converter tools to write the text backwards or from right to left and vertically instead of horizontally.

C ensorship Circum vention Tool: Psiphon J Psiphon is a censorship circumvention system that allows users to bypass firewalls and access blocked sites in countries where the Internet is censored It uses a secure, encrypted HTTP tunnel connection to receive requests from psiphonite to psiphonode which in turn transports the results back to the requested psophonite It acts as a web proxy for authenticated psiphonites, even works on mobile devices Psiphon 3 A.

SSH disconnected. HTTP proxy is rumha cn localhost poit VPN disconnected. SSH connecting. HTTP proxy is rumnq cn localhos! Unproxed autee iruixjifcoiit rem Urproxed. Rep rod u ctio n is S trictly Prohibited. It uses a secure, encrypted HTTP tunnel connection to receive requests from psiphonite to psiphonode, which in turn then transports the results back to the requested psophonite. It acts as a web proxy for authenticated psiphonites, and works on mobile browsers. The Your Freedom services makes accessible what is unaccessible to you, and they hide your network address from those who don't need to know.

This tool turns your PC into an uncensored, anonymous web proxy and an uncensored, anonymous SOCKS proxy that your applications can use, and if that's not enough, it can even get you connected to the Internet just as if you were using an unrestricted DSL or cable connection. J J Internet tools help identify if w eb users in China can access rem ote websites W h e n Ju st Ping and W e b S ite P u lse show "Packets lost" or "tim e-out" errors, chances are that the site is restricted.

If a "packets lost" error is received or there is a connection time-out message is displayed while connecting to your site, chances are that the site is blocked. To find out whether the website at xyz. It pings a website or IP address and displays the result as shown as follows:. Okay Crnany: C o l o a n. Okay Sweden. Pad ova Auatin. U n i tod Spain: Italy: U.

It simultaneously pops websites from around the globe. H 4 I ChM C42; l? J j ; t jn G-Zaoce. Google sets a cookie on user's system with a unique identifier that enables them to track user's web activities such as: e Search Keywords and habits Search results Websites visited. It automatically detects and cleans Google cookies each time you use your web browser. Jdy It allows you to access blocked content on the Internet with omitted advertisements.

A few anonymizers that are readily available in the market are listed as follows:. Spoofing IP Address IP spoofing refers to the procedure of an attacker changing his or her IP address so that he or she appears to be som eone else W h e n the victim replies to th e address, it goes back to the spoofed address and not to the attacker's real address. When spoofing, an attacker a fake IP in place of the attacker's assigned IP. W hen the attacker sends a connection request to the target host, the target host replys to the attacker's request.

But the reply is sent to the spoofed address. W hen spoofing an address that doesn't exist, the target replies to a nonexistent system and then hangs until the session times out, consuming target resources. IP spoofing using Hping2: Hping2 w w w. Both will have the same TTL if they are the same protocol. If the reply is from a different protocol, then you should check the actual hop count to detect the spoofed packets.

If the attacker knows the hop count between source and host, it will be very easy for the attacker to launch an attack. In this case, the test results in a false negative. Spoofed packets can be identified based on the identification number IP ID in the IP header that increases each time a packet is sent. This method is effective even when both the attacker and victim are on same subnet.

To identify whether the packet is spoofed or not, send a probe packet to the target and observe the IP ID number in the reply. If it is in the near value as the packet that you are checking, then it is not a spoofed packet, otherwise it is a spoofed packet. Sending a packet with spoofed The algorithm accomplishes the flow control based on the sliding window principle. This field represents the maximum amount of data that the recipient can receive and the maximum amount of data the sender can transmit without acknowledgement.

Thus, this field helps us to control data flow. W hen the window size is set to zero, the sender should stop sending more data. In general flow control, the sender should stop sending data once the initial window size is exhausted. The attacker who is unaware of the ACK packet containing window size information continues to send data to the victim. If the victim receives data packets beyond the window size, then the packets must be treated as spoofed. For effective flow control method and early detection of spoofing, the initial window size must be very small.

Most spoofing attacks occur during the handshake, as it is difficult to build multiple spoofing replies with the correct sequence number. Therefore, the flow control spoofed packet detection must be applied at the handshake. To check whether you are getting. If the sender sends an ACK with any data, then it means that the sender is the spoofed one. IP S p o o fin g C o u n te r m e a s u r e s Limit access to configuration information on a machine. IP Spoofing C o u n te rm e a su re s In ethical hacking, the ethical hacker also known as the pen tester, has to perform an additional task that a normal hacker doesn't follow, i.

This is essential because knowing security loopholes in your network is worthless unless you take measures to protect them against real hackers. As mentioned previously, IP spoofing is one of the techniques that a hacker employs to break into the target network. Therefore, in order to protect your network from external hackers, you should apply IP spoofing countermeasures to your network security settings. The following are a few IP spoofing countermeasures that you can apply:. Avoid trust relationships Attackers may spoof themselves as a trusted host and send malicious packets to you.

If you accept those packets by considering that the packets are sent by your trusted host, then you may get infected. Therefore, it is advisable to test the packets even when they come from one of your trusted hosts. You can avoid this problem by implementing password authentication along with trust-relationship-based authentication. Use firewalls and filtering mechanisms You should filter all the incoming and outgoing packets to avoid attacks and sensitive information loss.

The incoming packets may be the malicious packets coming from the attacker. If you do not employ any kind of incoming packet filtering mechanism such as a firewall, then the malicious packets may enter your private network and may cause severe loss. You can use access control lists ACLs to block unauthorized access. At the same time, there is also a possibility of insider attackers. These attackers may send sensitive information about your business to your competitors. This may also lead to great monetary loss or other issues. There is one more risk of outgoing packets, which is when an attacker succeeds in installing a malicious sniffing program running in hidden mode on your network.

These programs gather and send all your network information to the attacker without giving any notification. This can be figured out by filtering the outgoing packets. Therefore, you should give the same importance to the scanning of outgoing packets as that of the incoming packet data scanning. Use random initial sequence numbers Most of the devices chose their ISN based on timed counters.

If the attacker can predict the ISN, then he or she can make a malicious connection to the server and sniff your network traffic. To avoid this, risk you should use random initial sequence numbers. Ingress filtering Prohibiting spoofed traffic from entering the Internet is the best way to block it. This can be achieved with the help of ingress filtering. Ingress filtering applied on routers enhances the functionality of the routers and blocks spoofed traffic.

It can be implemented in many ways. Configuring and using access control lists ACLs that drop packets with source address outside the defined range is one way to implement ingress filtering. Egress filtering Egress filtering refers to a practice that aims at IP spoofing prevention by blocking the outgoing packets with a source address that is not inside.

Use encryption If you want to attain maximum network security, then use strong encryption for all the traffic placed onto the transmission media without considering its type and location. This is the best solution for IP spoofing attacks. Attackers usually tend to find targets that can be compromised easily. If an attacker wants to break into encrypted network, then he or she has to face a whole slew of encrypted packets, which is a difficult task.

Therefore, the attacker may try to find another target that can be easily compromised or may attempt other techniques to break into the network. Use the latest encryption algorithms that provide strong security. CEH S canning M eth o d o lo g y So far, we have discussed concepts such as what to scan, how to scan, how to detect vulnerabilities, and the respective countermeasures that are necessary to perform scanning pen testing. Now we will begin the action of scanning pen testing.

This section highlights the need to scan pen testing and the steps to be followed for effective pen testing. Pen testing a network for scanning vulnerabilities determines the network's security posture by identifying live systems, discovering open ports, associating services and grabbing system banners to simulate a network hacking attempt. S canning P en T e stin g The network scanning penetration test helps you to determine the network security posture by identifying live systems, discovering open ports and associated services, and grabbing system banners from a remote location, simulating a network hacking attempt.

You should scan or test the network in all possible ways to ensure that no security loophole is overlooked. S canning P en T e stin g C ontd Let's see step by step how a penetration test is conducted on the target network. Stepl: Host Discovery The first step of network penetration testing is to detect live hosts on the target network.

You can attempt to detect the live host, i. It is difficult to detect live hosts behind the firewall. These tools will help you to probe a server or host on the target network for open ports. Open ports are the doorways for attackers to install malware on a system. Therefore, you should check for open ports and close them if not necessary. This determines the operating system running on the target host of a network and its version. Once you know the version and operating system running on the target system, find. Try to gain control over the system and compromise the whole network.

These tools help you to find the vulnerabilities present in the target network. Document all the findings. S canning P en T e stin g C ontd Step 5: Draw Network Diagrams Draw a network diagram of the target organization that helps you to understand the logical connection and path to the target host in the network. The network diagrams provide valuable information about the network and its architecture. Step 7: Document all Findings The last but the most important step in scanning penetration testing is preserving all outcomes of tests conducted in previous steps in a document.

This document will assist you in finding potential vulnerabilities in your network. Once you determine the potential vulnerabilities, you can plan the counteractions accordingly. Thus, penetration testing helps in assessing your network before it gets into real trouble that may cause severe loss in terms of value and finance. Attackers use various scanning techniques to bypass firewall rules, logging mechanism, and hide themselves as usual network traffic.

Drawing target's network diagram gives valuable information about the network and its architecture to an attacker. HTTP Tunneling technology allows users to perform various Internet tasks despite the restrictions imposed by firewalls. Proxy is a network computer that can serve as an intermediary for connecting with other computers. A chain of proxies can be created to evade a traceback to the attacker. Read Free For 30 Days.

Flag for inappropriate content. Related titles. Carousel Previous Carousel Next. Jump to Page. Search inside document. Presented by Professionals. But the latest research disclosed other purposes of the same including recognizing susceptible VoIP targets, which could be used in toll fraud attacks. Ethical Hacking and Countermeasures Scanning Networks Exam Certified Ethical Hacker In a traditional sense, the access points that a thief looks for are the doors and windows. There may be many objectives for performing scanning, but here we will discuss the most common objectives that are encountered during the hacking phase: Discovering live hosts, IP address, and open ports of live hosts running on the network.

Ethical Hacking and Countermeasures Scanning Networks Exam Certified Ethical Hacker Identifying the vulnerabilities and threats: Vulnerabilities and threats are the security risks present in any system. Ethical Hacking and Countermeasures Scanning Networks Exam Certified Ethical Hacker The TCP protocol maintains stateful connections for all connection-oriented protocols across the Internet, and works the same as an ordinary telephone communication, in which one picks up a telephone receiver, hears a dial tone, and dials a number that triggers ringing at the other end until a person picks up the receiver and says, "Hello.

No urgent data Acknowledgement field Push function Reset sequence numbers significant The logs in the target system will disclose the connection. Commjnd Hosts Host sT v nmip SYN Port 80 Bill Sheela The client sends a FIN packet to the target port, and if the service is not running or if the port is closed it replies to you with the probe packet with an FIN No Response Attacker Reproduction Is Strictly Prohibited ICMP echo scanning is used to discover live machines by pinging all the machines in the target network.

O RANGE 6 6. Ethical Hacking and Countermeasures Scanning Networks Exam Certified Ethical Hacker Ensure that routing and filtering mechanisms cannot be bypassed using specific source ports or source-routing techniques. A more advanced fingerprinting technique depends on stack querying, which transfers the packets to the network host and evaluates packets based on the reply. The objective is to find patterns in the initial sequence of numbers that the TCP implementations choose while responding to a connection request.

The four areas that are typically noted to determine the operating system are: 9 9 9 9 TTL - W hat the operating system sets the Time To Live on the outbound packet W indow Size - hat the operating system sets the W indow size DF - Does the operating system set the Don't Fragment bit OS - Does the operating system set the Type of Service, and if so, at what Passive fingerprinting has to be neither fully accurate nor be limited to these four signatures. Tell a f nena The various steps this tool follows are: e e e 0 0 Data gathering Host identification Port scan Plug-in selection Reporting of data To obtain more accurate and detailed information from Windows-based hosts in a Windows domain, the user can create a domain group and account that have remote registry access privileges.

Features: 9 9 9 9 9 Selectively creates custom vulnerability checks Identifies security vulnerabilities and takes remedial action Creates different types of scans and vulnerability tests Helps ensure third party security applications offer optimum protection Performs network device vulnerability checks Module 03 Page Ethical Hacking and Countermeasures Copyright by EC-COUIICil All Rights Reserved.

Setup Service Packs and Up l0. It can automatically detect all subnets according to the IP addresses configured on multiple NICs of. Colasoft MAC Scanner es una herramienta diseada para administradores de redes y sistemas con la que podrn obtener con un simple click un completo listado con todas las direcciones MAC e IP que estn. Colasoft mac scanner 1. Fast Colasoft mac scanner 1. Let's face it — nothing beats real-world experience, and the closest you can come to that experience in a book is through practical exam- ples of packet analysis with real-world scenarios.

The first half of this book gives you the prerequisite knowledge you will need to understand packet analysis and Wireshark. The second half of the book is devoted entirely to practical cases that you could easily encounter in day-to-day network management. Whether you are a network technician, a network administrator, a chief information officer, a desktop technician, or even a network security analyst, you have a lot to gain from understanding and using the packet-analysis tech- niques described in this book.

Concepts and Approach I am generally a really laid-back guy, so when I teach a concept, I try to do so in a really laid-back way. This holds true for the language used in this book. It is very easy to get lost in technical jargon when dealing with technical con- cepts, but I have tried my best to keep things as casual as possible. I've made all the definitions clear, straightforward, and to the point, without any added fluff. After all, I'm from the great state of Kentucky, so I try to keep the big words to a minimum.

You'll have to forgive me for some of the backwoods country verbiage you'll find throughout the text. If you really want to learn packet analysis, you should make it a point to master the concepts in the first several chapters, because they are integral to understanding the rest of the book. The second half of the book is purely practical. You may not see these exact scenarios in your workplace, but you should be able to apply the concepts you learn from them in the situations you do encounter. Here is a quick breakdown of the contents of the chapters in this book: Chapter 1 : Packet Analysis and Network Basics What is packet analysis?

How does it work? How do you do it? This chap- ter covers the basics of network communication and packet analysis. Chapter 2: Tapping into the Wire This chapter covers the different techniques you can use to place a packet sniffer on your network. Chapter 3: Introduction to Wireshark Here, we'll look at the basics of Wireshark — where to get it, how to use it, what it does, why it's great, and all of that good stuff. Chapter 4: Working with Captured Packets After you have Wireshark up and running, you will want to know how to interact with captured packets. This is where you'll learn the basics.

Chapter 5: Advanced Wireshark Features Once you have learned to crawl, it's time to take off running. This chap- ter delves into the advanced Wireshark features, taking you under the hood to show you some of the less apparent operations. In order to understand how these protocols can mal- function, you first need to understand how they work.

Chapter 8: Basic Real-World Scenarios This chapter contains breakdowns of some common traffic and the first set of real-world scenarios. Each scenario is presented in an easy-to-follow format, where the problem, analysis, and solution are given. These basic scenarios deal with only a few computers and involve a limited amount of analysis — -just enough to get your feet wet.

Chapter 9: Fighting a Slow Network The most common problems network technicians hear about generally involve slow network performance. This chapter is devoted to solving these types of problems. Chapter Packet Analysis for Security Network security is the biggest hot-button topic in the information tech- nology area. Chapter 10 shows you some scenarios related to solving security-related issues with packet-analysis techniques. Chapter Wireless Packet Analysis This chapter is a primer on wireless packet analysis. It discusses the dif- ferences between wireless analysis and wired analysis, and includes some examples of wireless network traffic.

Appendix: Further Reading The appendix of this book suggests some other reference tools and web- sites that you might find useful as you continue to use the packet-analysis techniques you have learned. This means paying particular attention to the real-world scenarios in the last several chapters. There are some features of Wireshark that you will not use very often, so you may forget how they work.

Practical Packet Analysis is a great book to have on your bookshelf when you need a quick refresher about how to use a specific feature. I've also provided some unique charts, diagrams, and methodologies that may prove to be useful references when doing packet analysis for your job. In order to maximize the potential of this book, I highly recommend that you download these files and use them as you follow along with the examples.

Shortly after the release of the first edition of this book, I founded a c 3 nonprofit organization that is the culmina- tion of one of my biggest dreams. Rural students, even those with excellent grades, often have fewer oppor- tunities for exposure to technology than their city or suburban counterparts.

Established in , the Rural Technology Fund RTF seeks to reduce the digital divide between rural communities and their more urban and sub- urban counterparts. This is done through targeted scholarship programs, community involvement, and general promotion and advocacy of technology in rural areas. Our scholarships are targeted to students living in rural communities who have a passion for computer technology and intend to pursue further education in that field. I'm pleased to announce that percent of the author proceeds from this book go directly to the Rural Technology Fund in order to provide these scholarships.

Contacting Me I'm always thrilled to get feedback from people who read my writing. If you would like to contact me for any reason, you can send all questions, comments, threats, and marriage proposals directly to me at chris chrissanders. The best we can hope for is to be fully prepared with the knowledge and tools we need to respond to these types of issues. All network problems stem from the packet level, where even the prettiest looking applications can reveal their horrible implementations, and seemingly trustworthy protocols can prove malicious.

To better understand network problems, we go to the packet level. Here, nothing is hidden from us — nothing is obscured by misleading menu structures, eye-catching graphics, or untrust- worthy employees. At this level, there are no true secrets only encrypted ones. The more we can do at the packet level, the more we can control our network and solve problems.

This is the world of packet analysis. This book dives into the world of packet analysis headfirst. You'll learn how to tackle slow network communication, identify application bottlenecks, and even track hackers through some real-world scenarios. By the time you have finished reading this book, you should be able to implement advanced packet-analysis techniques that will help you solve even the most difficult problems in your own network.

In this chapter, we'll begin with the basics, focusing on network commu- nication, so you can gain some of the basic background you'll need to exam- ine different scenarios. Packet Analysis and Packet Sniffers Packet analysis, often referred to as packet sniffing or protocol analysis, describes the process of capturing and interpreting live data as it flows across a network in order to better understand what is happening on that network.

Packet analysis is typically performed by a packet sniffer, a tool used to capture raw network data going across the wire. Each program is designed with different goals in mind. A few popular packet-analysis programs are tcpdump, OmniPeek, and Wireshark which we will be using exclusively in this book. Evaluating a Packet Sniffer You need to consider a number of factors when selecting a packet sniffer, including the following: Supported protocols All packet sniffers can interpret various protocols. When choosing a sniffer, make sure that it supports the protocols you're going to use. The program you choose should fit your level of expertise.

If you have very little packet- analysis experience, you may want to avoid the more advanced command- line packet sniffers like tcpdump. On the other hand, if you have a wealth of experience, you may find an advanced program more appealing. As you gain experience with packet analysis, you may even find it useful to combine multiple packet-sniffing programs to fit particular scenarios. Cost The great thing about packet sniffers is that there are many free ones that rival any commercial products.

The most notable difference between commercial products and their free alternatives is their reporting engines. Commercial products typically include some form of fancy report-generation module, which is usually lacking or nonexistent in free applications. Program support Even after you have mastered the basics of a sniffing program, you may occasionally need support to solve new problems as they arise.

When evaluating available support, look for developer docu- mentation, public forums, and mailing lists. Although there may be a lack of developer support for free packet-sniffing programs like Wireshark, the communities that use these applications will often fill the gap. These communities of users and contributors provide discussion boards, wikis, and blogs designed to help you to get more out of your packet sniffer.

Operating system support Unfortunately, not all packet sniffers support every operating system. Choose one that will work on all the operating systems that you need to support. If you are a consultant, you may be required to capture and analyze packets on a variety of operating systems, so you will need a tool that runs on most operating systems. Also keep in mind that you will sometimes capture packets on one machine and review them on another. Variations between operating systems may force you to use a different application for each device.

How Packet Sniffers Work The packet-sniffing process involves a cooperative effort between software and hardware. This process can be broken down into three steps: Collection In the first step, the packet sniffer collects raw binary data from the wire. Typically, this is done by switching the selected network interface into promiscuous mode.

In this mode, the network card can listen to all traffic on a network segment, not only the traffic that is addressed to it. Conversion In this step, the captured binary data is converted into a readable form. This is where most advanced command-line packet sniffers stop. At this point, the network data is in a form that can be interpreted only on a very basic level, leaving the majority of the analysis to the end user.

Packet Analysis and Network Basics 3 Analysis The third and final step involves the actual analysis of the cap- tured and converted data. The packet sniffer takes the captured network data, verifies its protocol based on the information extracted, and begins its analysis of that protocol's specific features. How Computers Communicate In order to fully understand packet analysis, you must understand exactly how computers communicate with each other.

In this section, we'll examine the basics of network protocols, the Open Systems Interconnections OSI model, network data frames, and the hardware that supports it all. Protocols Modern networks are made up of a variety of systems running on many differ- ent platforms. To aid this communication, we use a set of common languages called protocols. A protocol stack is a logical grouping of protocols that work together. One of the best ways to understand protocols is to think of them as similar to the rules that govern spoken or written human languages.

Every language has rules, such as how verbs should be conjugated, how people should be greeted, and even how to properly thank someone. Protocols work in much the same fashion, allowing us to define how packets should be routed, how to initiate a connection, and how to acknowledge the receipt of data.

A protocol can be extremely simple or highly complex, depending on its function. Although the various protocols are often drastically different, many protocols commonly address the following issues: Connection initiation Is it the client or server initiating the connection? What information must be exchanged prior to communication? Negotiation of connection characteristics Is the communication of the protocol encrypted? How are encryption keys transmitted between com- municating hosts? Data formatting How is the data contained in the packet ordered? In what order is the data processed by the devices receiving it?

Error detection and correction What happens in the event that a packet takes too long to reach its destination? How does a client recover if it can- not establish communication with a server for a short duration? Connection termination How does one host signify to the other that communication has ended? What final information must be transmitted in order to gracefully terminate communication? The OSI model divides the network communications pro- cess into seven distinct layers, as shown in Figure This hierarchical model makes it much easier to understand network com- munication.

The application layer at the top represents the actual programs used to access network resources. The bottom layer is the physical layer, through which the actual network data travels. The protocols at each layer work together to ensure data is properly handled by the protocols at lay- ers above and below it. The OSI model is no more than an industry- recommended standard. Protocol developers are not required to follow it exactly. This is the only layer typically seen by end users, as it provides the interface that is the base for all of their network activities.

Presentation layer layer 6 This layer transforms the data it receives into a format that can be read by the application layer. The data encod- ing and decoding done here depends on the application layer protocol that is sending or receiving the data. The presentation layer also handles several forms of encryption and decryption used for securing data. Session layer layer 5 This layer manages the dialogue, or session between two computers. It establishes, manages, and terminates this connection among all communicating devices.

The session layer is also responsible for establishing whether a connection is duplex or half-duplex, and for gracefully closing a connection between hosts, rather than dropping it abruptly. Packet Analysis and Network Basics 5 Transport layer layer 4 The primary purpose of the transport layer is to provide reliable data transport services to lower layers. Because ensur- ing reliable data transportation can be extremely cumbersome, the OSI model devotes an entire layer to it.

The transport layer utilizes both connection-oriented and connectionless protocols. Certain firewalls and proxy servers operate at this layer. Network layer layer 3 This layer is responsible for routing data between physical networks, and it is one of the most complex of the OSI layers.

It is responsible for the logical addressing of network hosts for example, through an IP address. It also handles packet fragmentation, and in some cases, error detection. Routers operate at this layer. Data link layer layer 2 This layer provides a means of transporting data across a physical network. Its primary purpose is to provide an addressing scheme that can be used to identify physical devices for example, MAC addresses. Bridges and switches are physical devices that operate at the data link layer. Physical layer layer 1 The layer at the bottom of the OSI model is the physical medium through which network data is transferred.

This layer defines the physical and electrical nature of all hardware used, including voltages, hubs, network adapters, repeaters, and cabling specifications. The physical layer establishes and terminates connections, provides a means of sharing communication resources, and converts signals from digital to analog and vice versa. Table lists some of the more common protocols used at each individ- ual layer of the OSI model.

As we progress through this book, you will find that the interaction of protocols on different layers will shape your approach to network problems. Router issues will soon become "layer 3 problems" and software issues will be recognized as "layer 7 problems. The issue was the result of the user entering an incorrect password.

My colleague referred to this as a "layer 8 issue. This term is commonly used among those who live at the packet level. How does data flow through the OSI model? The initial data transfer on a network begins at the application layer of the transmitting system. Data works its way down the seven layers of the OSI model until it reaches the physical layer, at which point the physical layer of the transmitting system sends the data to the receiving system.

The receiving system picks up the data at its physical layer, and the data proceeds up the remaining layers of the receiving system to the application layer at the top. Services provided by various protocols at any given level of the OSI model are not redundant. For example, if a protocol at one layer provides a particu- lar service, then no other protocol at any other layer will provide this same service. Protocols at different levels may have features with similar goals, but they will function a bit differently. Protocols at corresponding layers on the sending and receiving computers are complementary.

For example, if a protocol on layer 7 of the sending computer is responsible for encrypting the data being transmitted, the corre- sponding protocol on layer 7 of the receiving machine is expected to be responsible for decrypting that data. Figure shows a graphical representation of the OSI model as it relates to two communicating clients.

You can see communication going from top to bottom on one client, and then reversing when it reaches the second client. For example, layer 2 can send and receive data only from layers 1 and 3. Data Encapsulation The protocols on different layers of the OSI model communicate with the aid of data encapsulation. Each layer in the stack is responsible for adding a header or footer — extra bits of information that allow the layers to communi- cate — to the data being communicated.

For example, when the transport layer receives data from the session layer, it adds its own header information to that data before passing it to the next layer. The encapsulation process creates a protocol data unit PDU , which includes the data being sent and all header or footer information added to it. As data moves down the OSI model, the PDU changes and grows as header and footer information from various protocols is added to it.

The PDU is in its final form once it reaches the physical layer, at which point it is sent to the destination computer. Understanding how encapsulation of data works can be a bit confusing, so we'll look at a practical example of a packet being built, transmitted, and received in relation to the OSI model. Keep in mind that as analysts, we don't often talk about the session or presentation layers, so those will be absent in this example and the rest of this book. For this process to take place, we must generate a request packet that is transmitted from our source client computer to the destination server computer.

Figure illustrates the data- encapsulation process in this example. We begin on our client computer at the application layer. We are brows- ing to a website, so the application layer protocol being used is HTTP, which will issue a command to download the file index. Once our application layer protocol has dictated what we want to accom- plish, our concern is with getting the packet to its destination.

The data in our packet is passed down the stack to the transport layer. Therefore, TCP serves as the transport layer protocol used to ensure reliable delivery of the packet. As a result, a TCP header is generated. This TCP header includes sequence numbers and other data that is appended to the packet, and ensures that the packet is properly delivered.

Having done its job, TCP hands the packet off to IP, which is the layer 3 protocol responsible for the logical addressing of the packet. IP creates a header containing logical addressing information and passes the packet along to Ethernet on the data link layer. Physical Ethernet addresses are stored in the Ethernet header. The packet is now fully assembled and passed to the physical layer, where it is transmitted as zeros and ones across the network.

The completed packet traverses the network cabling system, eventually reaching the Google web server. The web server begins by reading the packet from the bottom up, meaning that it first reads the data link layer, which contains the physical Ethernet addressing information that the network card uses to determine that the packet is intended for a particular server.

Once this information is processed, the layer 2 information is stripped away, and the layer 3 information is processed. The IP addressing information is read in the same manner as the layer 2 information to ensure proper addressing and that the packet is not fragmented. This data is also stripped away so that the next layer can be processed.

Layer 4 TCP information is now read to ensure that the packet has arrived in sequence. Then the layer 4 header information is stripped away, leaving only the application layer data, which can be passed to the web server appli- cation hosting the website. In response to this packet from the client, the server should transmit a TCP acknowledgment packet so the client knows its request was received followed by the index, html file.

Packet Analysis and Network Basics 9 All packets are built and processed as described in this example, regard- less of which protocols are used. But at the same time, keep in mind that not every packet on a network is generated from an application layer protocol, so you will see packets that contain only information from layer 2, 3, or 4 protocols.

Network Hardware Now it's time to look at network hardware, where the dirty work is done. We'll focus on just a few of the more common pieces of network hardware: hubs, switches, and routers. Hubs range from very small 4-port devices to larger port ones designed for rack mounting in a corporate environment.

Figure A typical 4-port Ethernet hub Because hubs can generate a lot of unnecessary network traffic and are capable of operating only in half-duplex mode they cannot send and receive data at the same time , you won't typically see them used in most modern or high-density networks switches are used instead. However, you should know how hubs work, since they will be very important to packet analysis when using the "hubbing out" technique discussed in Chapter 2. A hub is no more than a repeating device that operates on the physical layer of the OSI model.

It takes packets sent from one port and transmits repeats them to every other port on the device. For example, if a computer on port 1 of a 4-port hub needs to send data to a computer on port 2, the hub sends those packets to ports 1, 2, 3, and 4. The clients connected to ports 3 and 4 examine the destination Media Access Control MAC address field in the Ethernet header of the packet, and they see that the packet is not for them, so they drop discard the packet.

Figure illustrates an example in which computer A is transmitting data to computer B. When computer A sends this data, all computers connected to the hub receive it. Only computer B actually accepts the data; the other computers discard it. As an analogy, suppose that you sent an email with the subject line "Atten- tion all marketing staff" to every employee in your company, rather than to only those people who work in the marketing department.

The marketing department employees will know it is for them, and they will probably open it. The other employees will see that it is not for them, and they will probably discard it. You can see how this would result in a lot of unnecessary commu- nication and wasted time, yet this is exactly how a hub functions. The best alternatives to hubs in production and high-density networks are switches, which are full-duplex devices that can send and receive data synchronously. Computer B Computer D Figure The flow of traffic when computer A transmits data to computer 8 through a hub Switches Like a hub, a switch is designed to repeat packets.

However, unlike a hub, rather than broadcasting data to every port, a switch sends data to only the computer for which the data is intended. Switches look just like hubs, as shown in Figure Figure A rack-mountable port Ethernet switch Several larger switches on the market, such as Cisco-branded ones, are managed via specialized, vendor-specific software or web interfaces.

These switches are commonly referred to as managed switches. Managed switches provide several features that can be useful in network management, including the ability to enable or disable specific ports, view port specifics, make config- uration changes, and remotely reboot. Packet Analysis and Network Basics 1 1 Switches also offer advanced functionality when it comes to handling transmitted packets. In order to be able to communicate directly with specific devices, switches must be able to uniquely identify devices based on their MAC addresses, which means that they must operate on the data link layer of the OSI model.

Switches store the layer 2 address of every connected device in a CAM table, which acts as a kind of traffic cop. When a packet is transmitted, the switch reads the layer 2 header information in the packet and, using the CAM table as reference, determines to which port s to send the packet. Switches send packets only to specific ports, thus greatly reducing network traffic. Figure illustrates traffic flow through a switch. In this figure, com- puter A is sending data to only the intended recipient: computer B.

Multiple conversations can happen on the network at the same time, but information is communicated directly between the switch and intended recipient, not between the switch and all connected computers. A router is an advanced network device with a much higher level of function- ality than a switch or a hub.

A router can take many shapes and forms, but most have several LED indicator lights on the front and a few network ports on the back, depending on the size of the network. Figure shows an example of a router.

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Routers operate at layer 3 of the OSI model, where they are responsible for forwarding packets between two or more networks. The process routers use to direct the flow of traffic among networks is called routing. Several types of routing protocols dictate how different types of packets are routed to other networks.

Routers commonly use layer 3 addresses such as IP addresses to uniquely identify devices on a network. Computer B Computer D Figure ; The flow of traffic when computer A transmits data to computer 8 through a switch Routers 12 Chapter 1 in ii nil i 9 enteras v s Figure A low-level Cisco router suitable for use in o small to mid-sized network One way to illustrate the concept of routing is by using the analogy of a neighborhood with several streets. Think of the houses, with their addresses, as computers, and each street as a network segment, as shown in Figure From your house on your street, you can easily communicate with your neighbors in the other houses on the street.

This is similar to the operation of a switch that allows communication among all computers on a network segment. However, communicating with a neighbor on another street is like communicating with a computer that is not on the same segment. Figure Comparison of a routed network to neighborhood streets Referring to Figure , let's say that you're sitting at Vine Street and need to get to Dogwood Lane.

In order to do this, you must cross onto Oak Street, and then onto Dogwood Lane. Think of this as crossing network segments. If the device at The size and number of routers on a network will typically depend on the network's size and function. Personal and home-office networks may have only a small router located at the center of the network. A large corporate network might have several routers spread throughout various departments, all connecting to one large central router or layer 3 switch an advanced type of switch that also has built-in functionality to act as a router.

Figure shows the layout of a very common form of routed network. In this example, two separate networks are connected via a single router. If a computer on net- work A wishes to communicate with a computer on network B, the transmitted data must go through the router. Network A Network B Figure The flow of traffic when computer A transmits data to computer X through a router Traffic Classifications Network traffic can be divided among three main classes: broadcast, multicast, and unicast.

Each classification has a distinct characteristic that determines how packets in that class are handled by networking hardware. Broadcast Traffic A broadcast packet is one that is sent to all ports on a network segment, regard- less of whether that port is a hub or switch. All broadcast traffic is not created equally, however. There are layer 2 and layer 3 forms of broadcast traffic. Layer 3 also has a specific broadcast address. The highest possible IP address in an IP network range is reserved for use as the broadcast address.

For example, in a network configured with a In larger networks with multiple hubs or switches connected via different media, broadcast packets transmitted from one switch reach all the way to the ports on the other switches on the network, as they are repeated from switch to switch.

The extent to which broadcast packets travel is called the broadcast domain, which is the network segment where any computer can directly transmit to another computer without going through a router. Figure 14 Chapter 1 shows an example of two broadcast domains on a small network. Because each broadcast domain extends until it reaches the router, broadcast packets circulate only within this specified broadcast domain.

Figure : A broadcast domain extends to everything behind the current routed segment. Our earlier example describing how routing relates to a neighborhood also provides good insight into how broadcast domains work. You can think of a broadcast domain as being like a neighborhood street. If you stand on your front porch and yell, only the people on your street will be able to hear you. If you want to talk to someone on a different street, you need to find a way to speak to that person directly, rather than broadcasting yelling from your front porch.

Multicast Traffic Multicast is a means of transmitting a packet from a single source to multiple destinations simultaneously. The goal of multicasting is to simplify this pro- cess by using as little bandwidth as possible. The optimization of this traffic lies in the number of times a stream of data is replicated in order to get to its destination.

The exact handling of multicast traffic is highly dependent on its implementation in individual protocols. The primary method of implementing multicast is via an addressing scheme that joins the packet recipients to a multicast group, which is how IP multicast works. This addressing scheme ensures that the packets cannot be transmitted to computers to which they are not destined.

In fact, IP devotes an entire range of addresses to multicast. If you see an IP address in the Unicast Traffic A unicast packet is transmitted from one computer directly to another. The details of how unicast functions depend on the protocol using it. For example, consider a device that wishes to communicate with a web server. This is a one-to-one connection, so this communication process would begin with the client device transmitting a packet to only the web server. This form of communication is an example of unicast traffic. You misunderstand what is going on at this level of network communication before you can begin troubleshooting network issues.

In the next chapter, we will build on these concepts and discuss more advanced net- work communication principles. This is most often referred to by packet analysts as sniffing the wire, tapping the network, or tapping into the wire. Simply put, this is the process of placing a packet sniffer on a net- work in the correct physical location.

Unfortunately, sniffing packets is not as simple as plugging a laptop into a network port and capturing traffic. In fact, it is sometimes more difficult to place a packet sniffer on a network's cabling system than it is to actually ana- lyze the packets. The challenge with sniffer placement is that a large variety of networking hardware is used to connect devices. Figure illustrates a typical situation. Because the three main devices on a modern network hubs, switches, and routers each handles traffic differently, you must be very aware of the physi- cal setup of the network you are analyzing.

Figure : Placing your sniffer on the network Is sometimes the biggest challenge you will face.


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The goal of this chapter is to help you develop an understanding of packet-sniffer placement in a variety of different network topologies. But first, let's look at how we're actually able to see all the packets that cross the wire we're tapping into. Before you can sniff packets on a network, you need a network interface card NIC that supports a promiscuous mode driver. Promiscuous mode is what allows a NIC to view all packets crossing the wire. As you learned in Chapter 1, with network broadcast traffic, it's common for clients to receive packets that are not actually destined for them.

ARP, which is used to determine which MAC address corresponds to a particular IP address, is a crucial fixture on any network, and it's a great example of traffic sent to hosts other than the intended recipient.


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  • To find the matching MAC address, ARP sends a broadcast packet to every device on its broadcast domain in hopes that the correct client will respond. A broadcast domain the network segment where any computer can directly transmit to another computer without going through a router can consist of several computers, but only one client on that domain should be interested in the ARP broadcast packet that is transmitted.

    It would be terribly inefficient for every computer on the network to actually process the ARP broadcast packet. Instead, the NICs of the devices on the network for whom the packet is not destined recognize that the packet is of no use to them, and the packet is discarded rather than being passed to the CPU for processing.

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    The discarding of packets not destined for the receiving host improves processing efficiency, but it's not so great for packet analysts. As analysts, we typically want to see every packet sent across the wire so that we don't risk missing some crucial piece of information. When operating in promiscuous mode, the NIC passes every packet it sees to the host's processor, regardless of addressing. Once the packet makes it to the CPU, it can then be grabbed by a packet-sniffing application for analysis. For the purposes of this book, you must have a NIC and an operating sys- tem that support the use of promiscuous mode.

    The only time you do not need to sniff in promiscuous mode is when you want to see only the traffic sent directly to the MAC address of the interface from which you are sniffing. If you cannot legally obtain these privileges on a system, chances are that you should not be performing any type of packet sniffing on that particular network. Sniffing on a network that has hubs installed is a dream for any packet analyst. As you learned in Chapter 1 , traffic sent through a hub goes through every port connected to that hub.