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  • SQL 2012 Licensing Thoughts

    - by Geoff N. Hiten
    The only thing more controversial than new Federal Tax plans is new Licensing plans from Microsoft.  In both cases, everyone calculates several numbers.  First, will I pay more or less under this plan?  Second, will my competition pay more or less than now?  Third, will <insert interesting person/company here> pay more or less?  Not that items 2 and 3 are meaningful, that is just how people think. Much like tax plans, the devil is in the details, so lets see how this looks.  Microsoft shows it here: http://www.microsoft.com/sqlserver/en/us/future-editions/sql2012-licensing.aspx First up is a switch from per-socket to per-core licensing.  Anyone who didn’t see something like this coming should rapidly search for a new line of work because you are not paying attention.  The explosion of multi-core processors has made SQL Server a bargain.  Microsoft is in business to make money and the old per-socket model was not going to do that going forward. Per-core licensing also simplifies virtualization licensing.  Physical Core = Virtual Core, at least for licensing.  Oversubscribe your processors, that’s your lookout.  You still pay for  what is exposed to the VM.  The cool part is you can seamlessly move physical and virtual workloads around and the licenses follow.  The catch is you have to have Software Assurance to make the licenses mobile.  Nice touch there. Let’s have a moment of silence for the late, unlamented, largely ignored Workgroup Edition.  To quote the Microsoft  FAQ:  “Standard becomes our sole edition for basic database needs”.  Considering I haven’t encountered a singe instance of SQL Server Workgroup Edition in the wild, I don’t think this will be all that controversial. As for pricing, it looks like a wash with current per-socket pricing based on four core sockets.  Interestingly, that is the minimum core count Microsoft proposes to swap to transition per-socket to per-core if you are on Software Assurance.  Reading the fine print shows that if you are using more, you will get more core licenses: From the licensing FAQ. 15. How do I migrate from processor licenses to core licenses?  What is the migration path? Licenses purchased with Software Assurance (SA) will upgrade to SQL Server 2012 at no additional cost. EA/EAP customers can continue buying processor licenses until your next renewal after June 30, 2012. At that time, processor licenses will be exchanged for core-based licenses sufficient to cover the cores in use by processor-licensed databases (minimum of 4 cores per processor for Standard and Enterprise, and minimum of 8 EE cores per processor for Datacenter). Looks like the folks who invested in the AMD 12-core chips will make out like bandits. Now, on to something new: SQL Server Business Intelligence Edition. Yep, finally a BI-specific SKU licensed for server+CAL configurations only.  Note that Enterprise Edition still supports the complete feature set; the BI Edition is intended for smaller shops who want to use the full BI feature set but without needing Enterprise Edition scale (or costs).  No, you don’t get ColumnStore, Compression, or Partitioning in the BI Edition.  Those are Enterprise scale features, ThankYouVeryMuch.  Then again, your starting licensing costs are about one sixth of an Enterprise Edition system (based on an 8 core server). The only part of the message I am missing is if the current Failover Licensing Policy will change.  Do we need to fully or partially license failover servers?  That is a detail I definitely want to know.

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  • Python and a "time value of money" problem.

    - by jamieb
    (I asked this question earlier today, but I did a poor job of explaining myself. Let me try again) I have a client who is an industrial maintenance company. They sell service agreements that are prepaid 20 hour blocks of a technician's time. Some of their larger customers might burn through that agreement in two weeks while customers with fewer problems might go eight months on that same contract. I would like to use Python to help model projected sales revenue and determine how many billable hours per month that they'll be on the hook for. If each customer only ever bought a single service contract (never renewed) it would be easy to figure sales as monthly_revenue = contract_value * qty_contracts_sold. Billable hours would also be easy: billable_hrs = hrs_per_contract * qty_contracts_sold. However, how do I account for renewals? Assuming that 90% (or some other arbitrary amount) of customers renew, then their monthly revenue ought to grow geometrically. Another important variable is how long the average customer burns through a contract. How do I determine what the revenue and billable hours will be 3, 6, or 12 months from now, based on various renewal and burn rates? I assume that I'd use some type of recursive function but math was never one of my strong points. Any suggestions please? Edit: I'm thinking that the best way to approach this is to think of it as a "time value of money" problem. I've retitled the question as such. The problem is probably a lot more common if you think of "monthly sales" as something similar to annuity payments.

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  • How to reliably identify users across Internet?

    - by amn
    I know this is a big one. In fact, it may be used for some SO community wiki. Anyways, I am running a website that DOES NOT use explicit authentication of users. It's public as in open to everybody. However, due to the nature of the service, some users need to be locked out due to misbehavior. I am currently blocking IP addresses, but I am aware of the supposed fact that many people purposefully reset their DHCP client cache to have their ISP assign them new addresses. Is that a fact? I think it certainly is a lucrative possibility for some people who want to circumvent being denied access. So IPs turn out to be a suboptimal way of dealing with this. But there is nothing else, is it? MAC addresses don't survive on WAN (change from hop to hop?), and even if they did - these can also be spoofed, although I think less easily than IP renewal. Cookies and even Flash cookies are out of the question, because there are tons of "tutorials" how to wipe these, and those intent on wreaking havoc on Internet are well aware and well equipped against such rudimentary measures I would employ. Is there anything else to lean on? I was thinking heuristical profiling - collecting available data from client-side and forming some key with it, but have not gone as far as to implementing it - is it an option?

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  • Check for child duplicates

    - by ebb
    My console app will loop through each User to get their Websites, so that it can take new screenshots of them. However, to prevent taking screenshot of the same website twice I have to check whether there already has been taken screenshot of the website, while looping through another users websites. My current solution is: Database: User |--> ID: 1 |--> FirstName: Joe |--> ID: 2 |--> FirstName: Stranger Websites |--> ID: 1 |--> UserID: 1 |--> URL: http://site.com |--> ID: 2 |--> UserID: 2 |--> URL: http://site.com Console app: static void RenewWebsiteThumbNails() { Console.WriteLine("Starting renewal process..."); using (_repository) { var websitesUpdated = new List<string>(); foreach (var user in _repository.GetAll()) { foreach (var website in user.Websites.Where(website => !websitesUpdated.Contains(website.URL))) { _repository.TakeScreenDumpAndSave(website.URL); websitesUpdated.Add(website.URL); Console.WriteLine(new string('-', 50)); Console.WriteLine("{0} has successfully been renewed", website.URL); } } } } However, it seems wrong to declare a List for such a scenario, just to check whether a specific URL already has been added... any suggestions for an alternative way?

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  • AJAX filter MySQL results using checkboxes

    - by keepitnang
    I'm attempting to get to grips with displaying filterable MySQL data within a PHP page based on user checkbox selections. I have a database of domain names and the dates on which these will require renewal as per Nominet DAC information and I can get unfiltered data to display, but filtering results by domain extensions is proving tricky for me to accomplish. I should point out at this stage that I am a serious newcomer to many of the ideas I am trying to learn to work with here, so please be gentle. I have tried following some other articles on here also, but no dice. I have the following so far: HTML <input type="checkbox" class="extensions" name="extensions" value=".co.uk">.co.uk</input> <input type="checkbox" class="extensions" name="extensions" value=".org.uk">.org.uk</input> Script $('.extensions').live('click', function() { var all_boxes = $('.extensions'); var all_boxes_values = []; var i = 0; for (var i; i < all_boxes.length; i++) { if (all_boxes[i].checked) { all_boxes_values.push(all_boxes[i].value) } } var all_boxes_values_clean = all_boxes_values.join(", "); console.log(all_boxes_values_clean); $.get("sql-test.php", {q: all_boxes_values_clean}, function(result) { $("div#output").html(result); } )}); PHP $g = $_GET['q']; $extensionsql=""; $extension=1; if(isset($g)) { $extension=1; $param = "" . str_replace(",", "','", $_GET['q']) . ""; } And that's as far as I have gotten with my limited ability. What I would like to do next is search the column domainName for a string match and return the appropriate results to the user. Something to mimic something like the following but I'm not sure how to achieve it. Any help would be much appreciated: SELECT * FROM `refresh` WHERE `domainName` LIKE '%.co.uk%' AND renewalDate LIKE '%2012-06-30%' ORDER BY `domainName` ASC Thanks

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  • NTPD seems to delete all network interfaces

    - by Aurelin
    We have a couple of virtual interfaces configured on eth0 on a CentOS, and every now and then, they went down seemingly out of the blue. Now after going through the log files, I found out that apparently ntpd deletes all eth0 interfaces, and that dhclient automatically brings eth0 back up. The virtual interfaces, however, stay down which causes several of our websites to be inaccessible. Can someone explain to me why ntpd deletes interfaces? Can / should that be turned off, or can / should I configure dhclient to bring the virtual interfaces back up automatically, too? EDIT// The log files that I should've posted : Nov 12 13:10:28 raptor dhclient[20048]: DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x6a825e97) Nov 12 13:10:42 raptor dhclient[20048]: DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 8 (xid=0x24554092) Nov 12 13:10:42 raptor dhclient[20048]: DHCPOFFER from 96.126.108.78 Nov 12 13:10:42 raptor dhclient[20048]: DHCPREQUEST on eth0 to 255.255.255.255 port 67 (xid=0x24554092) Nov 12 13:10:42 raptor dhclient[20048]: DHCPACK from 96.126.108.78 (xid=0x24554092) Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #31 eth0, 50.116.50.97#123, interface stats: received=3255, sent=3256, dropped=0, active_time=1559394 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #32 eth0:0, 50.116.53.56#123, interface stats: received=3, sent=0, dropped=0, active_time=1559391 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #33 eth0:1, 66.175.211.192#123, interface stats: received=2, sent=0, dropped=0, active_time=1559389 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #34 eth0:2, 50.116.53.95#123, interface stats: received=3, sent=0, dropped=0, active_time=1559387 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #35 eth0:3, 97.107.132.32#123, interface stats: received=2, sent=0, dropped=0, active_time=1559385 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #36 eth0:4, 50.116.56.201#123, interface stats: received=2, sent=0, dropped=0, active_time=1559383 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #37 eth0:5, 66.175.212.121#123, interface stats: received=2, sent=0, dropped=0, active_time=1559381 secs Nov 12 13:10:42 raptor ntpd[2109]: Deleting interface #38 eth0:6, 66.175.215.137#123, interface stats: received=2, sent=0, dropped=0, active_time=1559379 secs Nov 12 13:10:44 raptor NET[1573]: /sbin/dhclient-script : updated /etc/resolv.conf Nov 12 13:10:44 raptor dhclient[20048]: bound to 50.116.50.97 -- renewal in 32692 seconds. Nov 12 13:10:45 raptor ntpd[2109]: Listening on interface #39 eth0, 50.116.50.97#123 Enabled The eth0 config : DEVICE="eth0" ONBOOT="yes" BOOTPROTO="dhcp" IPV6INIT="no" IPADDR=50.116.50.97 NETMASK=255.255.255.0 GATEWAY=50.116.50.1 And the virtual interfaces (I posted the first one only, they look the same for the most part) : # Configuration for eth0:0 DEVICE=eth0:0 BOOTPROTO=none # This line ensures that the interface will be brought up during boot. ONBOOT=yes # eth0:0 IPADDR=50.116.53.56 NETMASK=255.255.255.0

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  • Session Report: What’s New in JSF: A Complete Tour of JSF 2.2

    - by Janice J. Heiss
    On Wednesday, Ed Burns, Consulting Staff Member at Oracle, presented a session, CON3870 -- “What’s New in JSF: A Complete Tour of JSF 2.2,” in which he provided an update on recent developments in JavaServer Faces 2.2. He began by emphasizing that, “JavaServer Faces 2.2 continues the evolution of the Java EE standard user interface technology. Like previous releases, this iteration is very community-driven and transparent.” He pointed out that since JSF was introduced at the 2001 JavaOne Keynote, it has had a long and successful run and has found a home in applications where the UI logic resides entirely on the server where the model and UI logic is. In such cases, the browser performs fairly simple functions. However, developers can take advantage of the power of browsers, something that Project Avatar is focused on by letting developers author their applications so the UI logic is running on the client and communicating to the back end via RESTful web services. “Most importantly,” remarked Burns, “JSF 2.2 offers a really good migration path because even in the scope of one application you could have an app written with JSF that has its UI logic on the server and, on a gradual basis, you could migrate parts of the app over to use client-side technologies. This can be done at any level of granularity – per page or per collection of pages. It all depends on what you want to do.” His presentation, which focused on the basic new features of JSF 2.2, began by restating the scope of JSF and encouraged attendees to check out Roger Kitain’s session: CON5133 “Techniques for Responsive Real-Time Web UIs.” Burns explained that JSF has endured because, “We still need web apps that are maintainable, localizable, quick to build, accessible, secure, look great and are fun to use.” It is used on every continent – the curious can go here to check out where its unofficial usage is tracked. He emphasized the significance of the UI logic being substantially on the server. This: Separates Component Semantics from Rendering, Allows components to “own” their little patch of the UI -- encode/decode, And offers a well-defined lifecycle: Inversion of Control. Burns reminded attendees that JSR-344, the spec for JSF 2.2, is now on Java Community Process 2.8, a revised version of the JCP that allows for more openness and transparency. He then offered some tools for community access to JSF 2.2:    * Public java.net projects spec http://jsf-spec.java.net/ impl http://jsf.java.net/ Open Source: GPL+Classpath Exception    * Mailing Lists [email protected]                                Public readable archive, JSPA signed member read/write [email protected]                                     Public readable archive, any java.net member read/write                         All mail sent to jsr344-experts is sent to users. * Issue Tracker spec http://jsf-spec.java.net/issues/ impl http://jsf.java.net/issues/ JSF 2.2, which is JSR 344, has a Public Review Draft planned by December 2012 with no need for a Renewal Ballot. The Early Draft Review of JSR 344 was published on December 8, 2011. Interested developers are encouraged to offer their input. Six Big Ticket Features of JSF 2.2 Burns summarized the six big ticket features of JSF 2.2:* HTML5 Friendly Markup Support Pass through attributes and elements * Faces Flows* Cross Site Request Forgery Protection* Loading Facelets via ResourceHandler* File Upload Component* Multi-Templating He explained that he called it “HTML 5 friendly” because there is really nothing HTML 5 specific about it -- it could be 4. But it enables developers to use new elements that are present in HTML5 without having a JSF component library that is written to take advantage of those specifically. It gives the page author the ability to use plain HTML5 to write their page, but to still take advantage of the server-side available in JSF. He presented a demo showing JSF 2.2’s ability to leverage the expressiveness of HTML5. Burns then explained the significance of face flows, which offer function points and quantify how much work has taken place, something of great value to JSF users. He went on to talk about JSF 2.2.’s cross-site request forgery protection (CSRF) and offered details about how it protects applications against attack. Then he talked about JSF 2.2’s File Upload Component and explained that the final specification will have Ajax and non-Ajax support. The current milestone has non-Ajax support implemented. He then went on to explain its capacity to add facelets through ResourceHandler. Previously, JSF 2.0 added Facelets and ResourceHandler as disparate units; now in JSF 2.2 the two concepts are unified. Finally, he explained the concept of multi-templating in JSF 2.2 and went on to discuss more medium-level features of the release. For an easy, low maintenance way of staying in touch with JSF developments go to JSF’s Twitter page where every month or so, important updates are offered.

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  • Calculated Fields - Idiosyncracies

    - by PointsToShare
    © 2011 By: Dov Trietsch. All rights reserved Calculated Fields and some of their Idiosyncrasies Did you try to write a calculate field formula directly into the screen? Good Luck – You’ll need it! Calculated Fields are a sophisticated OOB feature of SharePoint, so you could think that they are best left to the end users – at least to the power users. But they reach their limits before the “Professionals “do, and the tough ones come back to us anyway. Back to business; the simpler the formula, the easier it is. Still, use your favorite editor to write it, then cut it and paste it to the ridiculously small window. What about complex formulae? Write them in steps! Here is a case in point and an idiosyncrasy or two. Our welders need to be certified and recertified every two years. Some of them are certifiable…., but I digress. To be certified you need to pass an eye exam, and two more tests – test A and test B. for each of those you have an expiry date. When renewed, each expiry date is advanced by two years from the date of renewal. My users wanted a visual clue so that when the supervisor looks at the list, she’ll have a KPI symbol telling her if anything expired (Red), is going to expire within the next 90 days (Yellow) or is not to be worried about (green). Not all the dates are filled and any blank date implies a complete lack of certification in the particular requirement. Obviously, I needed to figure the minimal of these 3 dates – a simple enough formula: =MIN([Date_EyeExam], {Date_TestA], [Date_TestB]). Aha! Here is idiosyncrasy #1. When one of the dates is a null, MIN(Date1, Date2) returns the non null date. Null is construed as “Far, far away”. The funny thing is that when you compare it to Today, the null is the lesser one. So a null it is less than today, but not when MIN is calculated. Now, to me the fact that the welder does not have an exam date, is synonymous with his exam being prehistoric, or at least past due. So here is what I did: Solution: Let’s set a blank date to 1/1/1800. How will we do that? Use the IF. IF([Field] rel relValue, TrueValue, FalseValue). rel is any relationship operator <, >, <=, >=, =, <>. If the field is related to the relValue as prescribed, the “IF” returns the TrueValue, otherwise it returns the FalseValue. Thus: =IF([SomeDate]="",1/1/1800,[SomeDate]) will return 1/1/1800 if the date is blank and the date itself if not. So, using this formula, if the welder missed an exam, the returned exam date will be far in the past. It would be nice if we could take such a formula and make it into a reusable function. Alas, here is a calculated field serious shortcoming: You cannot write subs and functions!! Aha, but we can use interim calculated fields! So let’s create 3 calculated fields as follows: 1: c_DateTestA as a calculated field of the date type, with the formula:  IF([Date_TestA]="",1/1/1800,[Date_TestA]) 2: c_DateTestB as a calculated field of the date type, with the formula:  IF([Date_TestB]="",1/1/1800,[Date_TestB]) 3: c_DateEyeExam as a calculated field of the date type, with the formula:  IF([Date_EyeExam]="",1/1/1800,[Date_EyeExam]) And now use these to get c_MinDate. This is again a calculated field of type date with the formula: MIN(c_DateTestA, cDateTestB, c_DateEyeExam) Note that I missed the square parentheses. In “properly named fields – where there are no embedded spaces, we don’t need the square parentheses. I actually strongly recommend using underscores in place of spaces in all the field names in your lists. Among other things, it makes using CAML much simpler. Now, we still need to apply the KPI to this minimal date. I am going to use the available KPI graphics that come with SharePoint and are always available in your 12 hive. "/_layouts/images/kpidefault-2.gif" is the Red KPI "/_layouts/images/kpidefault-1.gif" is the Yellow KPI "/_layouts/images/kpidefault-0.gif" is the Green KPI And here is the nested IF formula that will do the trick: =IF(c_MinDate<=Today,"/_layouts/images/kpidefault-2.gif", IF(cMinDate<Today+90,"/_layouts/images/kpidefault-1.gif","/_layouts/images/kpidefault-0.gif")) Nice! BUT when I tested, it did not work! This is Idiosyncrasy #2: A calculated field based on a calculated field based on a calculated field does not work. You have to stop at two levels! Back to the drawing board: We have to reduce by one level. How? We’ll eliminate the c_DateX items in the formula and replace them with the proper IF formulae. Notice that this needs to be done with precision. You are much better off in doing it in your favorite line editor, than inside the cramped space that SharePoint gives you. So here is the result: MIN(IF([Date_TestA]="",1/1/1800,[ Date_TestA]), IF([Date_TestB]="",1/1/1800,[ Date_TestB]), 1/1/1800), IF([Date_EyeExam]="",1/1/1800,[Date_EyeExam])) Note that I bolded the parentheses and painted them red. They have to match for this formula to work. Now we can leave the KPI formula as is and test again. This time with SUCCESS! Conclusion: build the inner functions first, and then embed them inside the outer formulae. Do this as long as necessary. Use your favorite line editor. Limit yourself to 2 levels. That’s all folks! Almost! As soon as I finished doing all of the above, my users added yet another level of complexity. They added another test, a test that must be passed, but never expires and asked for yet another KPI, this time in Black to denote that any test is not just past due, but altogether missing. I just finished this. Let’s hope it ends here! And OH, the formula  =IF(c_MinDate<=Today,"/_layouts/images/kpidefault-2.gif",IF(cMinDate<Today+90,"/_layouts/images/kpidefault-1.gif","/_layouts/images/kpidefault-0.gif")) Deals with “Today” and this is a subject deserving a discussion of its own!  That’s all folks?! (and this time I mean it)

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  • show hidden div tag from another page

    - by neueweblernen
    I'm trying to link to an all-inclusive FAQ page from various pages. The answers are contained in tags, nested within a line item of an unordered list housed by categories. The FAQ page has the following categories: Practical Nurse Exam Online Renewal Practice Hours etc. Under Practical Nurse Exam, there are sub categories, subjects, with questions below in tags that expand onClick. (e.g. Examination Day, Exam Results, etc.) Let's say I'm on a different page called Registration and there's a link to the FAQs for Exam Results. I'm able to link to the page and included the hashtag on the anchor or Exam Results, but it does not expand the subcategory. I've read this thread but it didn't work for me. Please help! The code is below: <script type="text/javascript"> function toggle(Info,pic) { var CState = document.getElementById(Info); CState.style.display = (CState.style.display != 'block') ? 'block' : 'none'; } window.onload = function() { var hash = window.location.hash; // would be "#div1" or something if(hash != "") { var id = hash.substr(1); // get rid of # document.getElementById(id).style.display = 'block'; } } </script> <style type="text/css"> .FAQ { cursor:hand; cursor:pointer; } .FAA { display:none; padding-left:20px; text-indent:-20px; } #FAQlist li { list-style-type: none; } #FAQlist ul { margin-left:0px; } headingOne{ font-family:Arial, Helvetica, sans-serif; color:#66BBFF; font-size:20px; font-weight:bold;} </style> Here's the body (part of it anyway) <headingOne class="FAQ" onClick="toggle('CPNRE', this)">PRACTICAL NURSE EXAM</headingOne> <div class="FAA" id="CPNRE"> <h3><a name="applying">Applying to write the CPNRE</a></h3> <ul id="FAQlist" style="width:450px;"> <li class="FAQ"> <p onclick="toggle('faq1',this)"> <strong>Q: How much does it cost to write the exam?</strong></p> <div class="FAA" id="faq1"> <b>A.</b> In 2013, the cost for the first exam writing is $600.00 which includes the interim license fee. See <a href="https://www.clpnbc.org/What-is-an-LPN/Becoming-an-LPN/Canadian-Practical-Nurse-Registration-Examination/Fees-and-Deadlines.aspx"> fee schedule</a>.</div> <hr /> </li> and here's the body of the other page that contains the link and the same script syntax as the all-inclusive FAQ page. This is just a test, that's not exactly what it will say: <a onclick="toggle('CPNRE', this)" href="file:///S|/Designs/Web stuff/FAQ all inclusive.html#applying"> click here</a>

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  • Network throughput issue (ARP-related)

    - by Joel Coel
    The small college where I work is having some very strange network issues. I'm looking for any advice or ideas here. We were fine over the summer, but the trouble began few days after students returned to campus in force for the fall term. Symptoms The main symptom is that internet access will work, but it's very slow... often to the point of timeouts. As an example, a typical result from Speedtest.net will return .4Mbps download, but allow 3 to 8 Mbps upload speed. Lesser symptoms may include severely limited performance transferring data to and from our file server, or even in some cases the inability to log in to the computer (cannot reach the domain controller). The issue crosses multiple vlans, and has effected devices on nearly every vlan we operate. The issue does not impact all machines on the network. An unaffected machine will typically see at least 11Mbps download from speedtest.net, and perhaps much more depending on larger campus traffic patterns at the time. There is one variation on the larger issue. We have one vlan where users were unable to log into nearly all of the machines at all. IT staff would log in using a local administrator account (or in some cases cached credentials), and from there a release/renew or pinging the gateway would allow the machine to work... for a while. Complicating this issue is that this vlan covers our computer labs, which use software called Deep Freeze to completely reset the hard drives after a reboot. It could just the same issue manifesting differently because of stale data on machines that have not permanently altered low-level info for weeks. We were able to solve this, however, by creating a new vlan and moving the labs over to the new vlan wholesale. Instigations Eventually we noticed that the effected machines all had recent dhcp leases. We can predict when a machine will become "slow" by watching when a dhcp lease comes up for renewal. We played with setting the lease time very short for a test vlan, but all that did was remove our ability to predict when the machine would become slow. Machines with static IPs have pretty much always worked normally. Manually releasing/renewing an address will never cause a machine to become slow. In fact, in some cases this process has fixed a machine in that state. Most of the time, though, it doesn't help. We also noticed that mobile machines like laptops are likely to become slow when they cross to new vlans. Wireless on campus is divided up into "zones", where each zone maps to a small set of buildings. Moving to a new building can place you in a zone, thereby causing you to get a new address. A machine resuming from sleep mode is also very likely to be slow. Mitigations Sometimes, but not always, clearing the arp cache on an effected machine will allow it to work normally again. As already mentioned, releasing/renewing a local machine's IP address can fix that machine, but it's not guaranteed. Pinging the default gateway can also sometimes help with a slow machine. What seems to help most to mitigate the issue is clearing the arp cache on our core layer-3 switch. This switch is used for our dhcp system as the default gateway on all vlans, and it handles inter-vlan routing. The model is a 3Com 4900SX. To try to mitigate the issue, we have the cache timeout set on the switch all the way down to the lowest possible time, but it hasn't helped. I also put together a script that runs every few minutes to automatically connect to the switch and reset the cache. Unfortunately, this does not always work, and can even cause some machines to end up in the slow state for a short time (though these seem to correct themselves after a few minutes). We currently have a scheduled job that runs every 10 minutes to force the core switch to clear it's ARP cache, but this is far from perfect or desirable. Reproduction We now have a test machine that we can force into the slow state at will. It is connected to a switch with ports set up for each of our vlans. We make the machine slow by connecting to different vlans, and after a new connection or two it will be slow. It's also worth noting in this section that this has happened before at the start of prior terms, but in the past the problem has gone away on it's own after a few days. It solved itself before we had a chance to do much diagnostic work... hence why we've allowed it to drag so long into the term this time 'round; the expectation was this would be a short-lived situation. Other Factors It's worth mentioning that we have had about half a dozen switches just outright fail over the last year. These are mainly 2003/2004-era 3Coms (mostly 4200's) that were all put in at about the same time. They should still be covered under warranty, buy HP has made getting service somewhat difficult. Mostly in power supplies that have failed, but in a couple cases we have used a power supply from a switch with a failed mainboard to bring a switch with a failed power supply back to life. We do have UPS devices on all but three of four switches now, but that was not the case when I started two and a half years ago. Severe budget constraints (we were on the Dept. of Ed's financially challenged institutions list a couple years back) have forced me to look to the likes of Netgear and TrendNet for replacements, but so far these low-end models seem to be holding their own. It's also worth mentioning that the big change on our network this summer was migrating from a single cross-campus wireless SSID to the zoned approach mentioned earlier. I don't think this is the source of the issue, as like I've said: we've seen this before. However, it's possible this is exacerbating the issue, and may be much of the reason it's been so hard to isolate. Diagnosis At first it seemed clear to us, given the timing and persistent nature of the problem, that the source of the issue was an infected (or malicious) student machine doing ARP cache poisoning. However, repeated attempts to isolate the source have failed. Those attempts include numerous wireshark packet traces, and even taking entire buildings offline for brief periods. We have not been able even to find a smoking gun bad ARP entry. My current best guess is an overloaded or failing core switch, but I'm not sure on how to test for this, and the cost of replacing it blindly is steep. Again, any ideas appreciated.

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