Home > Articles > Networking

  • Print
  • + Share This
This chapter is from the book

Appropriate Analysis: Some Analyzer Scenarios

Let's take a look at a couple scenarios in which analyzer use helped me out. In all cases, I was confronted by problems where we arrived at a theory, which then was proven through the use of the packet analyzer. This is how all of your analysis sessions should go.

I Can't Print, Again

Let's travel back to a problem we've discussed previously in Hour 19, "Internet and Intranet Troubleshooting: TCP/IP at Work." Remember how I found a UNIX host that would not spool more than one print job to a given network print server at one time, even if that print server had multiple printers attached to it? In other words, the host assumed that each print server only had one printer—a seriously wrong assumption! In this scenario, even though I had proved to myself that the host was at fault by using black box troubleshooting, I wanted evidence to submit to the vendor to prove that its stuff worked differently (wrongly) from other vendors' implementations of UNIX printing in order to try to force the vendor to fix it.

It was fairly easy to take a trace of this by specifying a capture filter of the print server's MAC address or TCP/IP address. Why not the UNIX host? Because the UNIX host had hundreds and hundreds of users, all accessing it via TCP/IP—had I specified the UNIX host, I would have had a little more data than I could handle.

I set up two test queues (queue1 and queue2) on the suspect host—one for each printer on the print server. As a "control experiment," I set up the same two queues on another host. I started the analyzer capture, went back to my desk, and quickly printed two jobs to the two test queues. I went back to the analyzer, stopped the capture, and saved it to disk, giving it the filename problem.

Then I did the exact same procedure, but used another host to print to the queues. I called this trace file good because this capture illustrated what happens with a UNIX host that's not brain dead. (Although the vendor didn't immediately act, our salesperson saw that we acted on this objective data and bought something else, which had good long-term effects on our leverage with this vendor—so it was worth doing. In fact, when we started having more problems with the machine and implementation of UNIX, we were given a new machine in reparation.)

Here are the important points to remember when submitting analyzer traces to a vendor:

  • Traces should be small. Filter as much as you can. If you have extraneous "stuff" during the initial capture, do a post-capture filter to remove everything but pertinent data.

  • Traces should be discrete. In particular, it is very useful to submit traces showing a "good" event versus a "bad" event.

  • Traces should be backed up with an objective and succinct description of the problem, describing what troubleshooting measures were taken.

Slow Databases 'R Us

Remember when we discussed file sharing databases in Hour 20, "In-depth Application Troubleshooting?" Unfortunately, these are still widely in use, and running into problems with these is pretty common. Let's take a look at the packet trace that I did in one case to prove that sequential record searching (rather than indexed) was in use on one database file. Again, this wasn't a problem in the vendor's 100-record database, but it was a huge problem once they sold it to my customer—who had tens of thousands of records.

The symptom of the problem was pressing Next Record on the work order system. Remember that databases are usually composed of more than one table, and more than one database file. To go to the "next record" in this work order database, another database was first consulted (to gather customer information to show on the screen). Because a sequential, rather than seeking (index-based) search was in use, this meant that finding the customer data could be quite a lengthy process!

How'd I prove this? Simply by capturing the network traffic generated at the workstation when the Next Record button was pressed. Then, I scrolled through the capture, and indeed, I found that sequential record reads were being used.

Here's how. Check out Figure 21.9. It shows the information that you'll need to start doing any type of file-and-print analysis. (This happens to be of an NCP session, but the basics are the same whether you're doing SMB or NFS.) First, you want to establish "where does the file get opened?" So, in packet #108, you see the OPEN (the details in the decode are what differentiate an OPEN from a CREATE) requested by the workstation. In packet #109, you see an important piece of data returned by the server: the file handle. A file handle is simply a number that refers back to the file. In subsequent file operations, you will not see the filename, just the handle.

Figure 21.9 When dealing with file-oriented captures, discovering the file handle that the server allocates is a good first step.

Now look at Figure 21.10. Packet #110 is the initial read request. Notice two things about the decode—the first of which is that this packet uses the same file handle as in Figure 21.9, that is, file handle 000092930200. (One analysis trick, whether you're dealing with SYN numbers, file handles, or any other long number: just remember the last four numbers when you're bouncing between packets. If there's a question, sure, compare the whole thing, but for quick reads, using the last four digits usually works out fine.) If a different file handle was displayed, you know you're dealing with the wrong file.

Figure 21.10 The initial read request for this problem starts at file offset 0—the beginning of the file.

Second, note that you're starting at file offset 0. This could be an index file, being checked from the beginning, but it's not. (The decode of Figure 21.9 shows that the file name is not an index.) What if it was an index? In this case, you would expect that the file seeking would start jumping around, as indexes are sorted, and typically use a binary search, a concept that we discussed in Hour 5, "The Napoleon Method: Divide and Conquer."

Scanning through the next couple of transactions tells the tale. Each one of the subsequent transactions looks similar to the one shown in Figure 21.11: It increments the offset by a small amount, which is basically the definition of what a sequential read sequence is. Again, this is a totally crazy and irresponsible thing to do if you are designing a fast database: Any field that gets searched needs some sort of index, which, when used, avoids sequential reads through binary search.

Figure 21.11 Future offsets in this problem show that sequential reads are occurring because file offsets keep incrementing in a predictable, sequential way.

At this point, you'd filter this trace to start at packet 108, and progress through perhaps 10–20 sequential reads. That should be enough for your vendor to get the idea. And, in our case, it was. We received fixed code within 30 days of reporting this. That's not bad.

Identifying a Station

In addition to analyzing and reporting bad network events, another use of an analyzer can be to identify workstations by MAC address using application data.

We've all been at sites where the MAC addresses weren't terribly well documented, so any MAC-related error was difficult to run down. For example, suppose Windows exclaims that there's a duplicate TCP/IP address on MAC address 00:00:C9:05:89:62. If you don't have switches and can't use the port-to-MAC table as we discussed in Hour 19, you might think that you're totally stuck.

Undocumented MAC addresses can be a nightmare. If your analyzer doesn't automatically identify network names for you, you might think that you're out of luck. The same goes for when your expert analyzer tells you that 00:08:02:55:29:2A is probably a bad network card and is causing many network errors.

But, no problem—you've got a wiretap, right? You can listen to all the traffic generated by this workstation, and it's likely that you'll get something that will identify the user. By taking a look at the data in the hexadecimal or character-oriented decode window, you can see various data that might lead you to identify the workstation's user (or department).

This is something that takes a little practice, but use your head and you'll get good at it in no time. For example, filtering on Telnet sessions will give you the entirety of a user's Telnet. Find the Password: prompt sent by the server, as in Figure 21.12, and you'll get the login name. The only problem is that you will likely have to assemble the password manually: As you go backward, the username data will present itself. To add to the fun, it's likely that the username will be "character-by-character," rather than the whole thing in one data packet. So, if the user name was "joe," you would see an "e" in packet #40's Telnet data section, and then an "o" in #37, with "j" coming right before that. The astute reader will point out that there are packets sent by the workstation (192.168.1.202) in between #45 and #40—what's up with that? Do the experiment: You'll see that they don't contain character data.

Figure 21.12 Telnet session usernames can be found in the packets immediately preceding the Password prompt.

Too much of a pain? Check out some of the Telnet data itself. You might see a report or a menu screen that only a particular user or department uses. This sort of use of an analyzer is a good opportunity to get good at reading your protocol decodes. But clearly, documenting your MAC addresses is the real solution.

TIP

When looking for the start of any TCP-based session, go down in the TCP decode and filter on synchronize=1. This will get you to the beginning of the session. It's the equivalent of saying "hello?" when you first pick up the telephone—the next steps, like "may I speak to Ms. So-and-so?" are likely in a nearby packet. Of course, encrypted authentications are going to make this a lot harder.

  • + Share This
  • 🔖 Save To Your Account

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