Home > Articles > Security > Network Security

Network Sniffers: Is Open Source Right for You?

There are commercial-grade sniffers available from manufacturers such as Fluke, Network General, and others. While these hardware tools can provide a much deeper level of analysis, you can build an inexpensive network sniffer using open source software and a low-end Intel PC. This chapter reviews several open source Ethernet sniffers.
This chapter is from the book

You can now properly secure and harden your systems and test your network for security vulnerabilities using proactive tools that help to keep your network healthy and secure. Now we will look at some tools that help you to act and react if you have a computer attack or security issue on your network in spite of all your preparations. Network sniffers fit into this category along with intrusion detection systems and wireless sniffers.

Chapter Overview

Concepts you will learn:

  • Network sniffer fundamentals

  • Ethernet history and operation

  • How to do safe and ethical network sniffing

  • Sample sniffer configurations

  • Network sniffer applications

Tools you will use:

Tcpdump, WinDump, and Ethereal

Simply put, a network sniffer listens or "sniffs" packets on a specified physical network segment. This lets you analyze the traffic for patterns, troubleshoot specific problems, and spot suspicious behavior. A network intrusion detection system (NIDS) is nothing more than a sophisticated sniffer that compares each packet on the wire to a database of known bad traffic, just like an anti-virus program does with files on your computer.

Sniffers operate at a lower level than all of the tools described thus far. Referring to the OSI Reference model, sniffers inspect the two lowest levels, the physical and data link layers.

OSI Layer Number

Layer Name

Sample Protocols

Layer 7

Application

DNS, FTP, HTTP, SMTP, SNMP, Telnet

Layer 6

Presentation

XDR

Layer 5

Session

Named Pipes, RPC

Layer 4

Transport

NetBIOS, TCP, UDP

Layer 3

Network

ARP, IP, IPX, OSPF

Layer 2

Data Link

Arcnet, Ethernet, Token Ring

Layer 1

Physical

Coaxial, Fiber Optic, UTP

The physical layer is the actual physical cabling or other media used to create the network. The data link layer is where data is first encoded to travel over some specific medium. The data link layer network standards include 802.11 wireless, Arcnet, coaxial cable, Ethernet, Token Ring, and many others. Sniffers are generally specific to the type of network they work on. For example, you must have an Ethernet sniffer to analyze traffic on an Ethernet LAN.

There are commercial-grade sniffers available from manufacturers such as Fluke, Network General, and others. These are usually dedicated hardware devices and can run into the tens of thousands of dollars. While these hardware tools can provide a much deeper level of analysis, you can build an inexpensive network sniffer using open source software and a low-end Intel PC.

This chapter reviews several open source Ethernet sniffers. I chose to feature Ethernet in this chapter because it is the most widely deployed protocol used in local area networks. The chances are that your company uses an Ethernet network or interacts with companies that do.

It used to be that the network world was very fragmented when it came to physical and data link layer transmission standards; there was no one dominant standard for LANs. IBM made their Token Ring topology standard for their LAN PCs. Many companies that used primarily IBM equipment used Token Ring because they had no other choice. Arcnet was popular with smaller companies because of its lower cost. Ethernet dominated the university and research environment. There were many other protocols, such as Apple's AppleTalk for Macintosh computers. These protocols were usually specific to a particular manufacturer. However, with the growth of the Internet, Ethernet began to become more and more popular. Equipment vendors began to standardize and focus on low-cost Ethernet cards, hubs, and switches. Today, Ethernet has become the de facto standard for local area networks and the Internet. Most companies and organizations choose it because of its low cost and interoperability.

A Brief History of Ethernet

Bob Metcalfe invented Ethernet in 1973 while at the Xerox Palo Alto Research Center. (This same innovative place also fostered the invention of the laser printer and the graphical user interface, among other things.) Bob and his team developed and patented a "multipoint data connection system with collision detection" that later became known as Ethernet. Bob went on to form a company specifically dedicated to building equipment for this new protocol. This company eventually became 3Com, one of the largest network companies in the world. Luckily, Ethernet was released into the public domain so other companies could build to the specification. This was not true of Token Ring and most of the other network protocols of the day. If Ethernet had been kept proprietary or limited to only one company's hardware, it probably wouldn't have developed into the dominant standard it is today. It was eventually adopted as an official standard by the International Electrical and Electronic Engineers (IEEE), which all but assured it wide acceptance by corporate and government users worldwide. Other standards have been developed based on Ethernet, such as Fast Ethernet, Gigabit Ethernet, and Wi-Fi.

Ethernet handles both the physical media control and the software encoding for data going onto a network. Since Ethernet is a broadcast topology, where every computer can potentially "talk" at once, it has a mechanism to handle collisions—when data packets from two computers are transmitted at the same time. If a collision is detected, both sides retransmit the data after a random delay. This works pretty well most of the time. However, this is also a downside to the Ethernet architecture. All computers attached to an Ethernet network are broadcasting on the same physical wire, and an Ethernet card on the network sees all the traffic passing it. The Ethernet card is designed to process only packets addressed to it, but you can clearly see the security implication here.

Imagine if the way the postal system worked was that a bag containing all the mail was dropped off at the end of the street and each resident picked through it for their mail and then passed it along. (It might be interesting to see who subscribed to Playboy and who was getting the past due notices.) This fictional system is not very secure nor does it make efficient use of everyone's time, but that is essentially how Ethernet was designed.

Nowadays, most Ethernet networks are switched to improve efficiency. This means that instead of each Ethernet port seeing all the traffic, it sees only traffic intended for the machine plugged into it. This helps alleviate some of the privacy and congestion issues, but plenty of broadcast traffic still goes to every port. Broadcast traffic is sent out to every port on the network usually for discovery or informational purposes. This happens with protocols such as DHCP, where the machine sends out a broadcast looking for any DHCP servers on the network to get an address from. Machines running Microsoft Windows are also notorious for putting a lot of broadcast traffic on the LAN.

Other broadcast types are often seen on Ethernet LANs. One is Address Resolution Protocol (ARP); this is when a machine first tries to figure out which MAC address relates to which IP address (see the sidebar on MAC addresses in Chapter 3). Ethernet networks use an addressing scheme called Medium Access Control (MAC) addresses. They are 12-digit hexadecimal numbers, and are assigned to the card at the factory. Every manufacturer has its own range of numbers, so you can usually tell who made the card by looking at the MAC address. If a machine has an IP address but not the Ethernet address, it will send out ARP packets asking, "Who has this address?" When the machine receives a reply, it can then send the rest of the communication to the proper MAC address. It is this kind of traffic that make Ethernet LANs still susceptible to sniffer attacks even when they use switching instead of broadcasting all traffic to every port. Additionally, if hackers can get access to the switch (these devices are often poorly secured), they can sometimes turn their own ports into a "monitor" or "mirror" port that shows traffic from other ports.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020