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The Sesame Street method: one of these things is not like the other ... The Sesame Street method is really simple, easy to apply, quick, and reasonably effective, ... – PowerPoint PPT presentation

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Title: Chapter 3 outline


1
Chapter 3 outline
  • What is network management?
  • Internet-standard management framework
  • Structure of Management Information SMI
  • Management Information Base MIB
  • SNMP Protocol Operations and Transport Mappings
  • Security and Administration
  • ASN.1
  • Network management in the real world
  • External pressures and constraints
  • Time issues
  • Tools of the trade

2
Tools of the Trade
  • Do not fear. There is still hope for the network
    manager. This hope comes in the form of
    different kinds of tools to assist in management.
  • Analytical skills
  • Procedures and supports
  • Software tools
  • Experience
  • Keep in mind that these tools tend to be
    expensive, hard to find, and do not necessarily
    do everything you need to do.
  • Nevertheless, having lots of options is good.
    Remember When your only tool is a hammer, every
    problem looks like a nail!

3
Analytical Approaches
  • There are many different analytical approaches
    that are useful in diagnosing problems and
    developing solutions that solve them.
  • In this course, we look at the following
    different techniques
  • The Delta method identifying network changes
  • The Napoleon method divide and conquer
  • The Sesame Street method one of these things is
    not like the other
  • The SOAP method Subjective data, Objective
    data, Analysis, and Plan
  • The Simple Simon method who has done this
    before
  • Scientific methods formal evaluation techniques

4
The Delta Method
  • We can be our own worst enemies sometimes.
  • A lot of problems dealt with in network
    management arise from changes made by humans in
    the network.
  • Sometimes there was a mistake in the change that
    led to the problem at hand.
  • Sometimes the change was fine, but there was a
    hidden dependency that broke when the change was
    made.
  • Sometimes the problem manifests itself
    immediately. Sometimes it remains hidden, only
    surfacing later when not expected (e.g. the next
    reboot).

5
The Delta Method
  • The worst kinds of changes are
  • Changes that were made and forgotten.
  • Changes that were made and not communicated.
  • Changes that were attempted, failed, and
    therewas no fallback position planned.
  • What does this tell us?
  • All changes must be planned and communicated.
  • All changes must be documented.
  • All changes must be immediately verified
    afterbeing made to uncover problems as soon as
    possible.
  • All changes must have a fallback position, just
    incase something unforeseen goes horribly wrong.

6
The Delta Method Troubleshooting
  • Suppose you did not follow the rules on the
    previous slide. What should you do?
  • Blame yourself. Always ask yourself the
    question What have I done lately? Be prepared
    to undo those changes to find out if you are the
    culprit.
  • Start asking other network managers if they have
    changed anything. Perhaps a coworker changed
    something, did not let you know, and that is now
    the source of the problem.
  • Ask vendors to see if they have made changes that
    you have adopted that could cause the problem.
  • Ask outsiders that connect with your network to
    see if they have made changes (e.g. your ISP).
  • Check with users with enough access privileges
    that they could cause the problem.

7
The Delta Method Planning for Change
  • Changes should not be implemented without a lot
    of thought and planning in advance!
  • Here is what should be done
  • Risk/benefit analysis. Each change can cause
    unforeseen problems. Does the benefits from the
    change outweigh the risks involved? Remember
    If it isnt broken, dont fix it!
  • Do a pilot test. Test out changes in an isolated
    non-production environment where they would do
    little damage if something went wrong.
  • Do incremental rollouts. After a pilot test, do
    not make the change everywhere at once. Do it in
    pieces to see if something happens along the way.
  • Have a fallback position. Make sure you can
    recover if things go wrong in your changes.

8
The Napoleon Method
  • This is basically a divide and conquer approach
    to diagnosing network problems.
  • The premise is that the location of a problem can
    be found more easily by splitting the problem
    area into smaller, manageable pieces.
  • Once you find the piece containing the problem,
    you repeat the divide and conquer process again,
    until you have completely isolated and located
    the problem at hand.
  • This approach can be useful when the delta method
    is not helping you solve a problem.
  • Not all changes are under your control, and many
    of them can be hidden and hard to detect.

9
The Napoleon Method Getting Started
  • When you first find out about a problem in the
    network, what should you do first?
  • See if it is a problem affecting only one user or
    host (a local problem) or with a large group of
    users or hosts (a systemic problem).
  • If it is local, you are done with systemic divide
    and conquer and can proceed to local analysis of
    the problem (which can include local divide and
    conquer as well).
  • If not, you need to collect more information and
    proceed with systemic divide and conquer.

10
The Napoleon MethodSystemic Divide and Conquer
  • The first step is to determine exactly which
    group of users or hosts is affected.
  • It is not likely that everyone with the problem
    has noticed or reported the situation.
  • Once you have a good idea of just who is
    affected, you need to figure out where those
    affected fit into your networks organization.
  • Basically, what do they have in common?
  • If need be, you may need to divide your network
    organization into smaller and smaller pieces
    until you find the portion that contains the
    problem.
  • You are then ready for local divide and conquer
    (and other local techniques).

11
The Napoleon MethodLocal Divide and Conquer
  • Think about your first exposure to search
    algorithms in first and second year.
  • You started with a linear search. Simple, but
    pretty expensive when there were a lot of items.
  • You then were introduced to the much faster
    binary search. Split the items in half, check
    for what you are looking for, and repeat in the
    appropriate half until you find it. This was a
    divide and conquer search algorithm!
  • This same general idea can help in further
    isolating and locating problems in networks and
    systems!

12
The Napoleon MethodLocal Divide and Conquer
  • A network example of local divide and conquer
  • Suppose you have a network connected by a series
    of hubs, and there is a problem on the network
    that is disrupting communications.
  • Instead of checking hub-by-hub, disconnect half
    of the hubs and see if the rest can communicate.
    If they can, the problem lies in the disconnected
    half.
  • Otherwise, the problem should lie in the half
    that is still connected.
  • Repeat this process on the half with the problem
    until the hub with the problem is located and
    isolated.
  • This approach can then be applied to individual
    ports on the hub to further localize the problem
    and to help find a solution.

13
The Napoleon MethodLocal Divide and Conquer
  • A host example of divide and conquer
  • Suppose you have a PC with Windows that fails to
    boot properly.
  • Instead of trying to disable individual drivers
    or modules started at boot time to locate the
    problem,first try a safe boot with no extras
    loaded.
  • If that works, add a group of them back to the
    system configuration, and try again. If it
    works, the problem lies in the group not added.
    If not, the problem is in this group.
  • By repeating the process over and over, the
    problem module can be located without much
    difficulty.

14
The Napoleon Method Drawbacks
  • This approach does not always work as well as
    one would like.
  • What if the problem involves multiple network
    components, instead of just one? An unlucky
    division of the network can result in two halves
    that work on their own, but not when put
    together.
  • What if the problem is intermittent? You might
    falsely assume the problem is in a location where
    it really is not, because it worked the one time
    when you tested the portion of the network it is
    in.
  • What if the problem is not a broken or not broken
    situation? If the problem is somewhere in the
    middle (for example, the network is not
    performing as fast as it could, but still works),
    this approach might not help out very much.

15
The Sesame Street Method
  • Think of the old Sesame Street song
  • One of these things is not like the others, One
    of these things just isnt the same!
  • The general principle involved is fairly simple.
  • Given a group of two or more items on a network,
    and one of these items is not functioning
    correctly, a comparison to a correctly working
    item should indicate what the problem is and how
    to solve it.
  • Typically, the way in which the items are
    different is also the reason the non-functioning
    item is broken.
  • Changing the configuration of the non-functioning
    item to be just like the configuration of a
    working item often fixes the problem.

16
The Sesame Street Method Ruling Out
  • Ruling out can be a very good problem solving
    technique for network management.
  • If you can determine what a problem is not, you
    are one step closer to figuring out what the
    problem is.
  • Examples
  • Suppose a user is having difficulty using a
    certain application on their workstation. You
    can rule out workstation problems by having the
    user try it on a different workstation. If it
    works there, it is not a workstation problem, but
    an account problem.
  • Suppose the only differences between a working
    computer and one that is not is the amount of
    memory, video card, and network adapter. If you
    give both the same memory, and the problem stays,
    you know it must be one of the other two.

17
The Sesame Street Method Good Comparisons
  • Making good comparisons is not always as easy as
    it sounds.
  • Are you really comparing the same thing? Make
    sure you compare apples to apples, and not to
    oranges!
  • Some identical things are intentionally
    configured differently. For example, routers and
    servers will often have vastly different
    configurations, even when they perform similar
    functions.
  • If different people or tools configure identical
    items, chances are good they could look very
    different but both still be functionally correct.
    The same people or tools may still configure
    identical things differently too the
    differences might not matter.

18
The Sesame Street Method A Good Tip
  • The Sesame Street method is really simple, easy
    to apply, quick, and reasonably effective, if
    comparisons can be made relatively easily.
  • To help do this, keep as many things the same as
    possible!
  • The more things are the same, the easier the
    comparisons are, and the easier it is to spot
    differences that could explain problems.
  • To do this
  • Develop standard procedures and scripts for
    configuring hardware, software, and user
    accounts.
  • Standardize on a few hardware and software
    platforms from a limited number of vendors unless
    there are compelling reasons not to.

19
The SOAP Method
  • The acronym SOAP stands for
  • Subjective data. This is what users report as
    their problem in the network, and any symptoms
    of the problem they have observed.
  • Objective data. This is what the network manager
    observes either directly, by investigation, or
    through data monitored and collected by
    management tools.
  • Analysis. This is what the network manager
    deduces to be the problem based on the above
    data.
  • Plan. This is how the network manager will treat
    the problem and perform follow-up.
  • With the plan in place, hopefully you are headed
    in the right direction.

20
The SOAP Method
  • This is usually a more rigorous and more formal
    method of attacking network problems.
  • You may want to try out the other methods first!
  • It can involve a lot of writing and tracking to
    record all of the data, analyses and plans.
  • Keep in mind that the problem might not be solved
    in the first attempt. The follow-up in the plan
    usually includes another iteration of SOAP if the
    plan does not successfully resolve the problem.
  • The SOAP method actually originated from the
    medical profession as a common tool for doctors
    to assist in patient diagnostics.

21
The SOAP Method Things to Keep in Mind
  • If the problem is complex, be prepared for
    several iterations of SOAP.
  • Sometimes, the plans of the first few runs
    through SOAP will be get more data, and then
    analyze the situation again.
  • Do not give up! The right data will eventually
    come by that will help resolve the situation.
  • If really stuck, get a consultation with someone
    else that has a fresh view of the problem with no
    preconceptions. Sometimes, you can be too close
    to the problem to effectively solve it.

22
The Simple Simon Approach
  • Sometimes, the simplest way to solve a problem
    is to find out if anybody else has had the same
    problem before.
  • If so, how did they solve it?
  • Every problem has to have some poor soul that is
    the first to discover it. Fortunately, chances
    are usually pretty good that it isnt you!
  • This can be a good reason not to live on the
    leading edge of technology sometimes!
  • If you are not the first to adopt new technology,
    chances are quite good you will not be the first
    torun into problems using it!

23
The Simple Simon ApproachTechnical Support
  • Most vendors have technical support sites with
    great features to help in management problems.
  • Searchable knowledge bases. (Do not use the main
    search feature on the vendors home page, as this
    usually hits lots of marketing press releases.
    Go to their technical support area and search
    from there.)
  • Frequently asked questions.
  • Technical specifications and documentation.
  • Downloaded patches and upgrades for various
    problems.
  • Discussion forums.
  • Contacts for further help.

24
The Simple Simon ApproachTechnical Support
  • When those avenues of technical support do not
    work out, sometimes direct contact is necessary.
  • Talking with another person can be quite helpful,
    but you have to be prepared first.
  • Gather all of your SOAP notes.
  • Make sure you have lists of the hardware and
    software involved, network configurations, time
    relationships, reproducibility information, and
    so on.
  • If you do not have this information, you are
    likely to get a brush off, and have the blame put
    on yourself, or another vendor involved in the
    problem.

25
The Simple Simon ApproachTechnical Support
  • Also keep in mind that some vendors have many
    tiers of technical support.
  • Some of it is available for free.
  • Some of it is available only to those willing to
    pay for it. Depending on how much you are
    willing to spend, you will get different levels
    of support.
  • Depending on budget availability, buying extended
    technical support from a vendor can save you a
    lot of headaches.
  • It can also save you time, and consequently
    money.
  • This is how you justify the expense when thetime
    comes!

26
The Simple Simon ApproachGoing to the Internet
  • The general Internet can be a good source of
    information (and misinformation) when it comes to
    support for network management problems.
  • Mailing lists can put you in contact with
    vendors, developers, and other experts that might
    be able to help you out.
  • Usenet newsgroups are good discussion forums can
    be a useful source of real world, unsanitized
    information that can help you out.
  • Search engines like Google can really help you
    sift through not just web pages, but also
    archived mailing lists, and Usenet too!

27
Scientific Methods
  • The previous approaches have been largely
    informal or technology driven.
  • The application of more formal, rigorous, and
    scientific methods and tools can also be useful
    in many cases.
  • They tend to be very time consuming, and
    therefore expensive, to carry out, but they can
    reveal information otherwise unobtainable.
  • For example, a correlation analysis of data
    collected during rigorous experimentation can
    give insight into the dependencies and
    relationships in measured data. This can be used
    to help determine causality which event or
    events introduced the studied problem into the
    network in the first place.

28
Scientific Methods Types of Evaluations
  • In formally evaluating a network of computers
    there are a few main techniques
  • Theoretical modeling. A mathematical model of
    the network is constructed to assist in reasoning
    about the performance and behaviour of the
    network.
  • Simulation. A simulation represents the
    operation and features of a network under a
    variety of different operating conditions.
  • Experimentation. A rigorous method of taking
    measurements from a real network environment (or
    real users of the network) under a variety of
    controlled operating conditions.

29
Scientific Methods Trade Offs
  • When can the evaluation techniques be used?
  • Models and simulations can be used before a
    network is even constructed or deployed.
  • Experimentation requires the network to be built
    and deployed for measurements to take place.
  • How do the different techniques scale?
  • Theoretical models do not scale well at all
    once the network is sufficiently large, modeling
    all of its components becomes impossible.
  • Simulations can handle medium sized environments.
    Once they get too large, it becomes difficult to
    accurately represent them in simulations.
  • Experimentation can be conducted on any sized
    network, although the volume of measured data in
    large networks can be overwhelming.

30
Scientific Methods Trade Offs
  • How much do the different techniques cost?
  • Theoretical models and simulations tend not to
    take too much time or money to use.
  • Experimentation can take a considerable amount of
    time, and money, since it uses the real network.
    If the network needs to be isolated during
    experimentation, it cannot be used for useful
    work, which again costs money in downtime.
  • How complex are the different techniques to
    develop?
  • All of the techniques can be reasonably complex
    and take time to develop, if they are to be used
    properly.

31
Scientific Methods Trade Offs
  • How accurate are the different techniques?
  • Theoretical models tend to have the least
    accuracy, since capturing the behaviour of the
    network is hard, especially when we do not fully
    understand it. Assumptions and simplifications
    tend to be needed.
  • Simulations tend to have better accuracy than
    models since they are representing the network in
    a more operational and less mathematical fashion.
    Fewer assumptions and simplifications tend to be
    needed.
  • Experimentation tends to have the best accuracy
    overall since you are measuring the real network
    under real conditions. One must remember the
    principle of certainty, though You cannot
    measure the behaviour of the network without
    influencing the behaviour in subtle ways.

32
Scientific Methods A Final Word
  • If you are interested in formal evaluations of
    computer systems and networks, you have to read
    the book
  • The Art of Computer Systems Performance
    Analysis Techniques for Experimental Design,
    Measurement, Simulation, and Modeling, by Raj
    Jain.
  • It is an invaluable resource for formal studies
    of computer network operations.
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