NET 211 - Wireless Networking

Chapter 11, Managing a Wireless LAN
Chapter 12: Wireless Network Troubleshooting and Optimization


This lesson covers two chapters about related topics. Objectives important to this lesson:

  1. Risks
  2. Security defenses for wireless LANs
  3. Tools to monitor a wireless network
  4. Maintaining a wireless LAN
  5. Troubleshooting interference
  6. Troubleshooting a WLAN configuration
  7. Troubleshooting wireless devices
Chapter 11

The author begins this chapter with another story that seems unrelated to the chapter objectives. Then he comes out of nowhere with a few pages about risk management. This topic is not even in the listed objectives, so I have added it as point 1 above.

The text introduces us to some vocabulary, illustrated by a story about someone who wants to buy new rims for his car. The story is useful, but not necessary to understand the terms.

  • Asset - information, hardware, software, or people that we care about
  • Threat - a potential form of loss or damage; many threats are only potential threats
  • Threat agent - a vector for the threat, a way for the threat to occur; could be a person, an event, or a program running an attack
  • Vulnerability - a weak spot where an attack is more likely to succeed
  • Exploit - a method of attack
  • Risk - the probability of a loss

The text tells us on page 395 that there are three options when dealing with risks. Mr. Ciampa actually presents a longer list in another book, so let's use that one. Some options are known by multiple names:

  • Avoidance, defense - make every effort to avoid your vulnerabilities being exploited; make the attack less possible, make the threat less likely to occur; avoid risk by performing the activity associated with the risk with greater care or in a different way
  • Transference - in general, letting someone else worry about it
    In the ITIL model, this is included in the definition of a service:
    "A service is a means of delivering value to customers by facilitating outcomes customers want to achieve without the ownership of specific costs and risks."
    A reader might misunderstand this statement, thinking that the customer does not pay anything. That is not the case. An IT service provider would assume the costs and risks of an operation in return for the customer's payment for the service. This can be done in-house or by outsourcing.
  • Mitigation - this method seeks to reduce the effects of an attack, to minimize and contain the damage that an attack can do; Incident Response plans, Business Continuity plans, and Disaster Recovery plans are all part of a mitigation plan
  • Acceptance - this counter-intuitive idea makes sense if the cost of an incident is minimal, and the cost of all of the other methods is too high to accept; the basic idea here is that it costs less just to let it happen in some cases
  • Terminate - simply stop the business activities that are vulnerable to a given threat; we cannot be exposed to a threat if we do not do what the threat affects

The author moves away from the general discussion of risks to discuss social engineering attacks. It begins with another story about people simply asking for access to a building and an office, and making a request for a password change. A primary aspect of social engineering is all about asking people for information they see no reason to keep secret.

Psychological Approaches

The following is a list of six attitudes/approaches a social engineer might take when making a request for a password change.

  • Authority - pretend to be someone who has the right to make the request
  • Intimidation - in an oppressive environment, it may be easy to use fear of what would happen if the request is not granted
  • Consensus/social proof - tell a believable lie that others have granted this request in the past
  • Scarcity - tell the victim that you are short on time, or you have to get this before it can't be done
  • Urgency - tell the victim that you need this right now, and that you will complete the red tape later
  • Familiarity/Liking - act like one of the family, especially one who appreciate the work the victim does for the company
  • Trust - use details about the organization to make it seem like you are a part of it

Someone who is practiced in manipulating people may be able to choose between these approaches easily, based on the attitude of the person on the other end of the phone, email, or messaging application. A skilled operator may be able to do much more if the can manipulate the person they are working on. Offering the person coffee, chocolate, or other simple gifts may make it easier to get them to do what you want.

Basic information about a target or a work site may be obtained from documents on a public facing website, a Facebook site, unshredded trash, or a phone call to the right person. Mr. Ciampa offers this advice to prospective social engineers in another text:

  • Ask for a little information from each of several people, building your required knowledge base without alerting the victims
  • Ask for what the victim is likely to be able to provide; don't ask for something inconsistent with the victim's job or role
  • Be pleasant and flattering, but in moderation
  • Don't ask for so much that it raises suspicion about you
  • Asking for help often triggers sympathy, thanking the victim helps them believe they have done something good

The best approach is to be a good actor, and to find the key to getting the right response from the victim. Take a look at this blog about acting. On the page that link leads to, there is some good advice about portraying emotion. In the context of this discussion, imagine yourself as the unsuspecting victim. Imagine the actress in the photos as the grifter. Which of her expressions is the one you relate to the most? Which is the one you want to help? Now, what do you look like when you react in sympathy to her? You are communicating to her that you are ready to hear and fulfill her requests. (If you can't see her face clearly enough, follow the link to her page. The photos are much clearer there, and her advice about showing emotion may be helpful to you.)

The text continues with a discussion of several other approaches under this heading.

  • Impersonation - An attacker might impersonate anyone who might seem to belong in the environment being surveilled or attacked. It is common to impersonate a help desk employee when calling a victim. It is also common to impersonate an employee, a delivery person, or a repair person when the ploy calls for infiltrating a site.
  • Phishing - Phishing is the solicitation of personal or company information, typically through an official looking email. Some variations on phishing:
    • Spear phishing - sending the email to specific people, customizing it to look like a message sent to them by an entity with some of their personal information already
    • Whaling - This is spear phishing but it focuses on big (wealthy or data rich) targets.
    • Pharming - sending an email that takes the person directly to a web site (the phisher's site) instead of asking the reader to follow a link
    • Google phishing - the phisher sets up a fake search engine that will send people to the phishing web site on specific searches (presumably it returns real search results on searches that would not lead to a page the phisher has prepared)
  • Spam - The section on spam, unsolicited email, seems out of place in this discussion. Most spam may only be looking for a customer, but some spam is sent with the intent to steal, abuse, and sell the payment information that a person might volunteer to provide.
  • Hoaxes - In the larger sense, all social engineering involves a hoax of some kind. First the grifter finds a mark, then he tells the mark the tale, and offers the deal. In the sense that the text means here, a hoax is distraction from reality, such as when the attacker pretends that there is a virus outbreak that is affecting the potential victim. It sets the idea in the victim's mind that the attacker is trying to help and should be assisted in his/her efforts.
  • Typo squatting - Most people are not great typists. The text explains that this is why other people (the bad ones) register domain names that are similar but not identical to real domains. They are hoping that the bad typists among us will misspell a URL and find ourselves on their site instead of the one we wanted, where we might volunteer information by trying to log in with credentials that can then be abused, sold, or ransomed. This technique is also called URL hijacking by the text.
  • Watering hole attack - The attacker determines that targets in the company/agency often visit a particular web site, called the watering hole in this scenario. It may be easier to infect that site than to attack the individuals directly, and then to take advantage of the real target.

Physical Approaches

  • Dumpster diving - Attackers doing research on a company can learn a lot from the trash the company discards. The text provides a table on page 73 with seven suggestions about things to look for in a target's trash.
  • Tailgating - The concept behind tailgating is simple. Someone who does not have authorization to pass through a secure entry point will gain access by simply following an authorized person through it, or by waiting for the door to open as someone exits through it. This might be done with or without the knowledge or cooperation of the authorized person.

The author returns to thoughts about defenses against attacks on page 398. He discusses three major areas of defense: security policies, training for users, and security processes.

Security policies

Let me borrow from another course we are offering this term. That text says that policies are inexpensive (they are just rules) but hard to implement, because they have no effect if people do not comply with them. So, what makes a good policy that people will follow? First, let's make a distinction between four terms:

  • Guideline - a guideline is a suggestion or a proposal that people should follow, but may choose not to follow (if they are idiots)
  • Policy - a policy is a plan that influences decisions;
    a policy is a rule for making decisions and choosing actions;
    a policy needs to be understood by those meant to follow it because it is a set of rules about what actions are acceptable and what actions are unacceptable
  • Standard - a statement of what must be done to comply with a policy;
    example: a standard might require that workstations bought for use in a particular area (e.g. systems development) must be either of two specific approved workstation models in order to comply with a policy that we only purchase workstations from a short list from a contracted vendor; a standard is typically more specific and narrow than a policy, and tells you how do what you need to do so you don't break the rules
  • Practice - if a policy and its standards are still a bit vague, a practice is a document that spells out more specifically what we must do to be in compliance;
    if standards are specific enough, a statement of practice may not be necessary;
    if different work areas, for example, must follow the rules in different ways, they may each have a statement of practice to tell staff how to comply in their jobs

Most texts have a list of requirements for a policy to be effective:

  • Must be properly written - understandable, relevant, clear
  • Must be distributed - despite the principle that ignorance of the law is not an excuse, it is not sensible to expect staff to comply with a policy they are not told about
  • Must be read - if we email a policy statement to all employees, does that guarantee that they all will read it?
  • Must be understood and agreed to - it is frequently amazing that people will agree completely with a policy as long as it applies to someone else, not them
  • Must be uniformly applied - the rules should be the same rules for everyone, or the policy will cause those who must follow it to resent those who do not and those who make and enforce the rules

Our text lists some purposes that a good security policy can serve. These purposes support the the other two areas, as well, so let's take a look at them:

  • It can describe an intention and a direction that the organization endorses, such as addressing security issues that caused a breach.
  • It can be a formal notification of a risk, the organization's choice about addressing that risk, and the expectations the organization has for the actions of its staff
  • It can promote awareness of security in general, which may carry over to other activities.
  • It can provide expectations to staff that their actions will be monitored and those actions will have consequences if the policy is not followed.
The text briefly discusses some steps frequently used in assessing the risks a company is facing. This is covered in more depth in some texts, but the author hits several high points. Typically, the steps would occur in this order:
  1. Identify assets - This means to create a list, to evaluate everything on it, and to determine which ones we must, should, or may not protect. This step may also prioritize the assets in order of importance to the company.
  2. Threat evaluation - Some assets are threatened only by specific threats, and some are much more likely to occur than others. Which ones? The text asks us to consider which threats are hazardous to our company (not every company's list will be the same) and which of those are the most dangerous.
  3. Vulnerability appraisal - You need to look at each identified threat, and determine which vulnerabilities of which assets they actually threaten. Where are we weak in protecting our assets?
  4. Risk assessment - The text is a bit vague about assigning a value to a risk. If we can't measure it, it isn't science, according to common wisdom, so let me introduce a formula from another security text.

    Let's consider some vocabulary that will help:
    • Likelihood (L)- the probability that a threat will be realized (actually happen); in this method, it will be a number from .1 to 1.0. That's how we measure probability, isn't it? 0 means it won't happen, 1 means it will, and anything in between is how probable the event is.
    • Value (V) - the monetary value of the asset; this may be expressed as the income we lose if it is compromised and/or the cost to replace the asset; alternatively, this may be a relative value compared to other assets
    • Mitigation (M) - the percentage of the risk that we have protected against
    • Uncertainty (U) - a fudge factor to express our confidence (or lack of it) in the other numbers; this is expressed as a percentage of the rest of the equation

    • The text observes that some risks have well known values. If we have to calculate one, we might do it like this:

      Risk = (V * L) - (V * M) + U * ( (V * L) - (V * M) )

      Assume the Value of an asset is 200.
      If the Likelihood of a threat being realized is 60%, the first term in this equation would be 200 * .6 = 120

      Let's assume the amount of protection (Mitigation) for this asset is 40%, so the second term would be 200 * .4 = 80

      The calculation for U depends on the rest of the equation. If we are only 90% sure of our Mitigation protection, the Uncertainty for this calculation is 10%, but what do we do with it? We multiply the uncertainty factor (10%) times the rest of the equation. So the third term would be ( (V*L) - (V*M) ) *  .1 = 40 * .1 = 4

      So for this example, Risk = (200 * .6) - (200 * .4) + .1 * ( (200 * .6) - (200 * .4) ) = 44
      Another way of looking at this might be to say that V * L is our likely loss if unprotected. V * M is the amount of the loss that we are protecting. The difference between the two is our probable loss, if we protect it. Finally, we add a percentage to the probable loss to reflect our uncertainty in the figures.

      This method will give us a number for each risk, so we can compare them to each other, and spend the most effort defending the right things.
  5. Risk mitigation - So what do we do to protect our risks, now that they are rated and prioritized? It depends on the risk, but the first step is usually to create security policies that apply to each risk, sometimes multiple policies.

The text discusses several types of policies:

  • Acceptable use policy - What are users allowed to do with our assets, and just as importantly, what are they not allowed to do? Everyone needs to be made aware of most policies, but this one is critical.
  • Password policy - A typical password policy sets rules about the age at which they expire, their minimum length, their required complexity, and how often a specific password may be reused. The text reminds us that a policy can contain more than the prompts a user will see when he/she is setting a new password. Advice about what makes a good password and what makes a poor password should also be included in the policy that is communicated to users.
  • Wireless policy - To relate the discussion back to this course, a wireless policy might state when personal wireless devices may or may not connect to the company network, matching rules for company owned wireless devices, whether encryption is required, whether company information may be stored or transmitted across what kind of network links. It is often part of this policy that company information shall never be transmitted across an unencrypted channel.

The text offers some general advice about writing a good security policy on page 402. The point is that if we always trust everyone, we have no security. If we never trust anyone, we have high security, but very little ease of use of our systems. The best level of security is usually one that allows people to do their job while protecting the most sensitive assets with the strongest protection. One way to do this is to make very sure we are allowing access only to the right people, then to allow them full access. As the text points out, there are extreme cases in which only the strongest security should be used, but those are usually rare.

In addition to publishing and enforcing security policies, another area of security is making users aware of security issues through training and awareness programs. There should be specific training for various activities, general awareness notices and information for all employees, and updated information when systems or policies are changed. The text offers a list of events that should seen as appropriate times to give this kind of information to users:

  • When hiring new staff
  • When our systems are attacked
  • When staff are promoted or change jobs
  • When there are annual or quarterly events like retreats or group meetings
  • When software changes
  • When hardware changes

The text moves on to discuss physical security for our installations. To understand the discussion, we should make sure we understand two phrases:

  • Physical assets - people, hardware, and supporting systems, which includes buildings and their various parts
  • Physical security - protecting the organization's physical assets, which includes designing and maintaining methods of protection

A thief who can steal your hardware can afford to take as much time as he needs to harvest information from it, which makes physical security as important as logical security.

The list of major physical controls below is a bit longer than the one in our text. It covers a few more ideas.

  • Walls, fences, and gates - obvious barriers make it clear to people that they are not allowed to walk beyond a certain point; gates are obvious points of access, but they are also filter points if you require staff to show permission to pass through them; these apply to external and internal environments
  • Guards - putting a guard on a gate, a door, or an asset allows you to set rules for passage and usage that can be interpreted by a human being or referred to an authorizing level of management
  • Dogs - guard dogs should probably appear as a subset of guards, whether they are working with handlers or left to patrol a sealed environment; a dog can sense things (noises, aromas) that a human guard cannot
  • ID cards (badges) - can be just a token or a photo ID, and may have a magnetic stripe, a computer chip, or an RFID; ID cards are both a proof of authorization and a problem: they need to be collected when an employee leaves their job, regardless of who decided they were leaving; the text describes tailgating, the practice of passing through a door that senses an authorization code by following someone who actually has authorization when you a) forgot yours, b) decided to be lazy, or c) are not authorized; it is the last variation we worry about, so some secure centers require that everyone passing a control point show their badge to the sensor to count heads; the text mentions the use of ID operated turnstiles, which are effective in metering traffic
  • Locks - as indicated above, some locks are opened with credentials; some locks require a key, and others require the intervention of an operator (e.g. guard, receptionist); biometric locks may be the most sophisticated locks: that means that unless they are sophisticated they won't work well
    • A door that stays locked if the electronic lock fails has a fail-secure lock.
    • A door that becomes unlocked if the electronic lock fails has a fail-safe lock. Since safe and secure are usually synonyms, this makes no sense. You just have to know which is which.
  • Cable locks - Devices that are meant to be moved are often built with little slots that may be used with cables which attach to desks, tables, or other structural features in the workplace. The idea is that if something is locked down, it is less likely to be stolen. It can still be stolen if the thief has a tool to cut the cable, and if the cable is securing your docking station, that means the thief may steal it as well as your laptop.
  • Mantrap - a vestibule or airlock with two doors that both lock if someone tries to pass through the second door to a secure area and fails; the idea is to alert security to a possible intrusion while containing the intruder
  • Video monitoring - allows recording of events, also allows fewer guards to watch over more areas by watching several screens at once; this typically adds a delay to response time, and may only be useful for collecting data after an event
  • Alarm systems - commonly associated with the opening of a door, may be triggered by sensors (motion, infrared, touch plates)

We return to wireless concerns on page 407. The author observes that the tools generally included with a wireless device only cover the senses of that device and will not give us much information about the network itself or other devices on it. He recommends using some features generally found on APs, such as the event log that records the devices that have associated with that AP.

The rest of the chapter repeats information we have seen on SNMP and introduces RMON, a Remote Network Monitoring utility that uses the SNMP protocol. Some advice is offered at the end of the chapter about maintenance of network equipment, but it adds little to the ideas about wireless networks.

Chapter 12

The last chapter we will cover in this course is Chapter 12, which is about troubleshooting. The author tells us that we should begin troubleshooting problems by determining which category the problem is part of. He lists three major categories:

  • RF interference - Although we are concerned with any interference, such as the EMI that can be generated by electric motors, for wireless LANs we care mostly about interference in the RF bands.

    Undesired signals from devices outside our network create what is usually called noise. The text suggests that we use a spectrum analyzer to find the RF noise floor, the background RF level in a given environment. Our signals must be stronger than this level if we are to hear them over that noise. We should assume that there will always be a noise floor in any environment.
    The text remarks on page 431 that interference can come from other wireless network devices, microwave ovens, cordless phones, wireless video cameras, microwave links, and wireless game controllers. This interference is mainly in the 2.4 GHz band. There can also be interference in the 5 GHz band from newer cordless phones, radar, perimeter sensors, and satellite devices.

    In the graphic above, taken with Acrylic Home, we see that there are two APs on channel 1 (there are actually five), and at least six on channel 6 (there are actually nine). In this case, the devices on channel 6 are interfering with each other a great deal because there are too many at nearly the same signal strength. A solution to this problem is addressed below.

    The text refers to interference on specific portions of the RF band as narrowband interference. Such interference from television, radio, and satellite transmitters typically does not affect wireless frequencies, but it can do so if the signal is very strong, as may happen when you are close to their transmitter. This would be an argument for not using wireless LANs inside a TV or radio station.

    Wideband interference is when a signal crosses over several frequencies, such as the entire usable 2.4 GHz band. As noted in the example above, you need to remove the device causing the interference, move your LAN, or go to a wired solution. When all else fails, remember that fibre optic network are immune to EMI and RFI.

    All-band Interference - The text explains that there are special problems when you have trouble with Frequency Hopping Spread Spectrum (FHSS) systems because they cover many frequencies over an entire band. This technology competes with regular wireless LAN use. The text tells us there are proposals to deal with this, but none are available as real solutions.

    Weather Interference - As noted earlier in the text, weather can refract an RF signal when it passes through weather that causes the air to change in density, and precipitation can cause RF deflection.

    Troubleshooting advice:
    • Use a spectrum analyzer to measure RF interference frequently. Things change, so you should watch out for those changes. You will not notice RF interference if you only use a packet sniffer.
    • Look for interference from the devices listed above, but watch out for new sources.
    • Maintain a suitable fade margin so that your system does not fall apart when a noise source suddenly increases in power.
    • Separate antennas as much as possible, which will result in proper coverage of desired areas, and less overlap of signals.

  • WLAN configuration settings - Several settings that an administrator can set for a wireless LAN can affect performance of that network. For example, if all WLANs in a given area use the same channel by default, there is a high probability of cochannel interference if they are are all close to each other. Note the proper assignment of channels in the two systems shown below. None of the adjacent WLANs uses the same channels as another WLAN that it overlaps. In the case of the 5 MHz WLANs in the image on the right, none of the WLANs should have a problem with adjacent channel interference. Each of the channels used is far enough away from those being used nearby that there should be no problems from this kind of interference.

    The text mentions incorrect power settings, which are not available on consumer equipment, only on commercial access points. Assuming you are using configurable equipment, you may want to consider whether increasing the power of an AP is worthwhile. If the AP can reach the device, but the device cannot reach the AP, there was no point to increasing the power. The text recommends a directional antenna for the AP, which may help in the situation on pages 434 and 435. It would also help to have another AP on the far side of the coverage area.

    There are some bullet points on page 436 that concern factors that can affect throughput on a network, in addition to those listed above.
    • AP processor speed - OK, but what are we going to do about it?
    • Distance from the AP - The obvious solution is to locate the AP and move closer to it.
    • Number of users on an AP - I have searched for an acceptable answer to this one, but there seems to be disagreement about how many users are too many.
    • Packet size - As we discussed before, smaller packets are better in most cases, and the network should manage that for us.

  • Problems with the wireless device (as opposed to problems from the other two sources) - The text discusses some common problems and offers a few suggestions about resolving them.
    • Near/Far - If a device is very close to an AP (near) and another is significantly distant from it (far), the near device may be transmitting a signal that is so strong relative to the far device that the AP only notices the near one. The text suggests moving the devices or changing their power levels, but this is only practical when the devices are stationary. Perhaps it would be desirable to place tables, desks, or seats in a circle around the AP in order to equalize the service it can perform for all users.
    • Hidden Nodes - As described previously, two devices may be located within range of an AP but not in range of each other, which results in collisions at the AP when both devices transmit. Again, the text addresses a solution that applies to a workplace with static locations. The best solution offered is to ad another AP for more coverage.
    • Windows Connection - The text presents a set of steps that a client on a Windows device will go through when connecting to an AP. This is interesting, but not very useful for troubleshooting. A possible exception is the note about APIPA addressing on the bottom of page 439. These are special addresses in a range that is otherwise never used, that are self assigned when a DHCP server cannot be reached. This feature needs to be turned on for a client to produce such an address, but it could be turned on as a way to notice when your DHCP server is not providing addresses to clients.
    • Troubleshooting steps -
      You can't attach to an AP if your device and the AP don't speak a common protocol.
      Make sure the preshared key is correct.
      If the AP filters on MAC addresses, it will exclude any device whose MAC address is missing or entered incorrectly.
      If the device has a switch to turn off its WiFi system, make sure the switch is set to ON. The ON and OFF positions are not clearly marked on most devices.