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  • Can I transform this asynchronous java network API into a monadic representation (or something else

    - by AlecZorab
    I've been given a java api for connecting to and communicating over a proprietary bus using a callback based style. I'm currently implementing a proof-of-concept application in scala, and I'm trying to work out how I might produce a slightly more idiomatic scala interface. A typical (simplified) application might look something like this in Java: DataType type = new DataType(); BusConnector con = new BusConnector(); con.waitForData(type.getClass()).addListener(new IListener<DataType>() { public void onEvent(DataType t) { //some stuff happens in here, and then we need some more data con.waitForData(anotherType.getClass()).addListener(new IListener<anotherType>() { public void onEvent(anotherType t) { //we do more stuff in here, and so on } }); } }); //now we've got the behaviours set up we call con.start(); In scala I can obviously define an implicit conversion from (T = Unit) into an IListener, which certainly makes things a bit simpler to read: implicit def func2Ilistener[T](f: (T => Unit)) : IListener[T] = new IListener[T]{ def onEvent(t:T) = f } val con = new BusConnector con.waitForData(DataType.getClass).addListener( (d:DataType) => { //some stuff, then another wait for stuff con.waitForData(OtherType.getClass).addListener( (o:OtherType) => { //etc }) }) Looking at this reminded me of both scalaz promises and f# async workflows. My question is this: Can I convert this into either a for comprehension or something similarly idiomatic (I feel like this should map to actors reasonably well too) Ideally I'd like to see something like: for( d <- con.waitForData(DataType.getClass); val _ = doSomethingWith(d); o <- con.waitForData(OtherType.getClass) //etc )

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  • MySQL get content from web page (or other network resource)

    - by Rescommunes
    Is it possible to open a curl like object in MySQL? What I would like to do is create procedure which would check to see if a certain value is returned from a specific URL like http://example.com/inschedule?id=200&time=20m. The returned result would be a simple string like 1 or 0. I know it is better to have a script do this by putting a entry into a table etc. However, it would be much less complex for me to be able to do it this way. Thanks

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  • Ubuntu Wired network(ethernet does not work)

    - by badnaam
    It was working just fine, until the other day I yanked it out. The wireless works just fine on the same router. If I login to a windows 7 instance on this dual boot laptop then the ehternet works just fine. So it's not a hardware, cable or router issue. The card even gets an ip, but I can't connect to the internet. Here are the details from route, iptables, ifconfig, ping etc. Any ideas? I have been struggling with this for day, none seems to have an answer. http://pastie.org/954816

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  • Uniquely identifying mobile devices over a network for webforms

    - by Eric
    I'm designing a system for mobile devices that can be assigned only to one job at a time. So I need to be able to know which mobile device is being used by accessing it's own unique static IP address or its device ID. I don't want to assign an ID myself for every machine that comes in which is why a static IP would work great. However, in trying to retrieve the client ip address I'm retrieving the wireless router's ip or some other ip which is not the mobile device's ip. I want to store that ip in a table and control which jobs are assigned to it. How can I accomplish this? I've tried the following but I'm getting the wireless ip: var hostEntry = Dns.GetHostEntry(Dns.GetHostName()); var ip = ( from addr in hostEntry.AddressList where addr.AddressFamily.ToString() == "InterNetwork" select addr.ToString() ).FirstOrDefault(); I'd rather not set a cookie if there exists a better alternative. TIA!

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  • Use Network Services for FDT

    - by WillDonohoe
    Hi everybody, I've recently started using FDT, for a while I was using FlashDevelop, it had a really handy feature in Compiler options where you can set UseNetworkServices to false which would stop the compiled swf from connecting to the internet and became very useful for running standalone flash apps without security warnings when loading in an external xml file etc. Does anybody know if FDT has a similar function? If there isn't a way, then no worries, I can compile the project in Flash Develop, however it would be best if I can do it from FDT. Cheers guys, Will

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  • Get machine name for remote computer on local network

    - by durza
    Hi, I've 2 machines with names Comp1, Comp2. There is a DNS name for them, that mask them as one, let say DNSName. I get IP addresses for both machines via Dns.GetHostEntry("DNSName"). But when I try get Dns.GetHostEntry(ipAddress) entry.HostName always contains DNSName. I found some way to get name through WMI. But our policy doesn't allow WMI on remote machines. I can do parsing of nbstat -a output, but I would like to do some clean aproach to this. Is there some way?

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  • [C++] Passing around objects to network packet handlers ?

    - by xeross
    Hey, I've been writing a networking server for a while now in C++ and have come to the stage to start looking for a way to properly and easily handle all packets. I am so far that I can figure out what kind of packet it is, but now I need to figure out how to get the needed data to the handler functions. I had the following in mind: Have a map of function pointers with the opcode as key and the function pointer as value Have all these functions have 2 arguments, packet and ObjectAccessor ObjectAccessor class contains various functions to fetch various items such as users and alike Perhaps pass the user's guid too so we can fetch it from the objectaccessor I'd like to know the various implementations others have come up with, so please comment on this idea and reply with your own implementations. Thanks, Xeross

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  • Possible to use Javascript to access the client side's network(knowingly)

    - by Earlz
    I recently found an exploit in my router to basically give me root access. The catch? There is a nonce hidden form value that is randomly generated and must be sent in for it to work that makes it difficult to do "easily" So basically I'm wanting to do something like this in javascript: get http://192.168.1.254/blah use a regex or similar to extract the nonce value put the nonce value into a hidden field in the current page submit the form by POST to http://192.168.1.254/blah complete with the nonce value and other form values I want to send in. Is this at all possible using only HTML and Javascript? I'm open to things like "must save HTML file locally and then open", which I'm thinking is one way around the cross domain policy. But anyway, is this at all possible? I'm hoping for this to be able to run from at least Firefox and Chrome. The audience for this is those with some technical know how.

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  • New ways for backup, recovery and restore of Essbase Block Storage databases – part 2 by Bernhard Kinkel

    - by Alexandra Georgescu
    After discussing in the first part of this article new options in Essbase for the general backup and restore, this second part will deal with the also rather new feature of Transaction Logging and Replay, which was released in version 11.1, enhancing existing restore options. Tip: Transaction logging and replay cannot be used for aggregate storage databases. Please refer to the Oracle Hyperion Enterprise Performance Management System Backup and Recovery Guide (rel. 11.1.2.1). Even if backups are done on a regular, frequent base, subsequent data entries, loads or calculations would not be reflected in a restored database. Activating Transaction Logging could fill that gap and provides you with an option to capture these post-backup transactions for later replay. The following table shows, which are the transactions that could be logged when Transaction Logging is enabled: In order to activate its usage, corresponding statements could be added to the Essbase.cfg file, using the TRANSACTIONLOGLOCATION command. The complete syntax reads: TRANSACTIONLOGLOCATION [ appname [ dbname]] LOGLOCATION NATIVE ?ENABLE | DISABLE Where appname and dbname are optional parameters giving you the chance in combination with the ENABLE or DISABLE command to set Transaction Logging for certain applications or databases or to exclude them from being logged. If only an appname is specified, the setting applies to all databases in that particular application. If appname and dbname are not defined, all applications and databases would be covered. LOGLOCATION specifies the directory to which the log is written, e.g. D:\temp\trlogs. This directory must already exist or needs to be created before using it for log information being written to it. NATIVE is a reserved keyword that shouldn’t be changed. The following example shows how to first enable logging on a more general level for all databases in the application Sample, followed by a disabling statement on a more granular level for only the Basic database in application Sample, hence excluding it from being logged. TRANSACTIONLOGLOCATION Sample Hyperion/trlog/Sample NATIVE ENABLE TRANSACTIONLOGLOCATION Sample Basic Hyperion/trlog/Sample NATIVE DISABLE Tip: After applying changes to the configuration file you must restart the Essbase server in order to initialize the settings. A maybe required replay of logged transactions after restoring a database can be done only by administrators. The following options are available: In Administration Services selecting Replay Transactions on the right-click menu on the database: Here you can select to replay transactions logged after the last replay request was originally executed or after the time of the last restored backup (whichever occurred later) or transactions logged after a specified time. Or you can replay transactions selectively based on a range of sequence IDs, which can be accessed using Display Transactions on the right-click menu on the database: These sequence ID s (0, 1, 2 … 7 in the screenshot below) are assigned to each logged transaction, indicating the order in which the transaction was performed. This helps to ensure the integrity of the restored data after a replay, as the replay of transactions is enforced in the same order in which they were originally performed. So for example a calculation originally run after a data load cannot be replayed before having replayed the data load first. After a transaction is replayed, you can replay only transactions with a greater sequence ID. For example, replaying the transaction with sequence ID of 4 includes all preceding transactions, while afterwards you can only replay transactions with a sequence ID of 5 or greater. Tip: After restoring a database from a backup you should always completely replay all logged transactions, which were executed after the backup, before executing new transactions. But not only the transaction information itself needs to be logged and stored in a specified directory as described above. During transaction logging, Essbase also creates archive copies of data load and rules files in the following default directory: ARBORPATH/app/appname/dbname/Replay These files are then used during the replay of a logged transaction. By default Essbase archives only data load and rules files for client data loads, but in order to specify the type of data to archive when logging transactions you can use the command TRANSACTIONLOGDATALOADARCHIVE as an additional entry in the Essbase.cfg file. The syntax for the statement is: TRANSACTIONLOGDATALOADARCHIVE [appname [dbname]] [OPTION] While to the [appname [dbname]] argument the same applies like before for TRANSACTIONLOGLOCATION, the valid values for the OPTION argument are the following: Make the respective setting for which files copies should be logged, considering from which location transactions are usually taking place. Selecting the NONE option prevents Essbase from saving the respective files and the data load cannot be replayed. In this case you must first manually load the data before you can replay the transactions. Tip: If you use server or SQL data and the data and rules files are not archived in the Replay directory (for example, you did not use the SERVER or SERVER_CLIENT option), Essbase replays the data that is actually in the data source at the moment of the replay, which may or may not be the data that was originally loaded. You can find more detailed information in the following documents: Oracle Hyperion Enterprise Performance Management System Backup and Recovery Guide (rel. 11.1.2.1) Oracle Essbase Online Documentation (rel. 11.1.2.1)) Enterprise Performance Management System Documentation (including previous releases) Or on the Oracle Technology Network. If you are also interested in other new features and smart enhancements in Essbase or Hyperion Planning stay tuned for coming articles or check our training courses and web presentations. You can find general information about offerings for the Essbase and Planning curriculum or other Oracle-Hyperion products here; (please make sure to select your country/region at the top of this page) or in the OU Learning paths section, where Planning, Essbase and other Hyperion products can be found under the Fusion Middleware heading (again, please select the right country/region). Or drop me a note directly: [email protected]. About the Author: Bernhard Kinkel started working for Hyperion Solutions as a Presales Consultant and Consultant in 1998 and moved to Hyperion Education Services in 1999. He joined Oracle University in 2007 where he is a Principal Education Consultant. Based on these many years of working with Hyperion products he has detailed product knowledge across several versions. He delivers both classroom and live virtual courses. His areas of expertise are Oracle/Hyperion Essbase, Oracle Hyperion Planning and Hyperion Web Analysis. Disclaimer: All methods and features mentioned in this article must be considered and tested carefully related to your environment, processes and requirements. As guidance please always refer to the available software documentation. This article does not recommend or advise any explicit action or change, hence the author cannot be held responsible for any consequences due to the use or implementation of these features.

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  • Azure eBook Update #1 &ndash; 16 authors so far!

    - by Eric Nelson
    I just wanted to share with folks where we are up to with the Windows Azure eBook (Check out the original post for full details) I have had lots of great submissions from folks with some awesome stuff to share on Azure. Currently we have 16 authors and 25 proposed articles. There is still a couple of days left to submit your proposal if you would like to get involved (see the original post ) and some topic suggestions below for which we don’t currently have authors. It is official – I’m excited! :-) Article Area Accepted Wikipedia Explorer: A case study how we did it and why. CaseSetudy Optional Patterns for the Windows Azure Platform (picking up 1 or 2 patterns that seem to be evolving) Architecture Optional Azure and cost-oriented architecture. Architecture Yes Code walkthrough of a comprehensive application submitted to newCloudApp contest CaseSetudy Yes Principles of highly scalable apps on Azure Compute Optional Auto-Scaling Azure Compute Yes Implementing a distributed cache using memcached with worker roles Interop Yes Building a content-based router service to direct requests to internal HTTP endpoints Compute Optional How to debug an Azure app by with a custom TraceListener & the AppFabric Service Bus AppFabric Yes How to host Java apps in Azure Interop Yes Bing Maps Tile Servers using Azure Blog Storage Interop Yes Tricks for storing time and date fields in Table Storage Storage Yes Service Runtime in Windows Azure Compute Yes Azure Drive Storage Optional Queries in Azure Table Storage Optional Getting RubyOnRails running on Azure Interop Yes Consuming Azure services within Windows Phone Interop Yes De-risking Your First Azure Project Architecture Yes Designing for failure Architecture Optional Connecting to SQL Azure In x Minutes SQLAzure Yes Using Azure Table Service as a NoSQL store via the REST API Storage Yes Azure Table Service REST API Storage Optional Threading, Scalability and Reliability in the Cloud Compute Yes Azure Diagnostics Compute Yes 5 steps to getting started with Windows Azure Introduction Yes The best tools for working with Windows Azure Tools Author Needed Understanding how SQL Azure works SQLAzure Author Needed Getting started with AppFabric Control Services AppFabric Author Needed Using the Microsoft Sync Framework with SQL Azure SQLAzure Author Needed Dallas - just a TV show or something more? Dallas Author Needed Comparing Azure to other cloud offerings Interop Author Needed Hybrid solutions using Azure and on-premise Interop Author Needed

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  • ASMLib

    - by wcoekaer
    Oracle ASMlib on Linux has been a topic of discussion a number of times since it was released way back when in 2004. There is a lot of confusion around it and certainly a lot of misinformation out there for no good reason. Let me try to give a bit of history around Oracle ASMLib. Oracle ASMLib was introduced at the time Oracle released Oracle Database 10g R1. 10gR1 introduced a very cool important new features called Oracle ASM (Automatic Storage Management). A very simplistic description would be that this is a very sophisticated volume manager for Oracle data. Give your devices directly to the ASM instance and we manage the storage for you, clustered, highly available, redundant, performance, etc, etc... We recommend using Oracle ASM for all database deployments, single instance or clustered (RAC). The ASM instance manages the storage and every Oracle server process opens and operates on the storage devices like it would open and operate on regular datafiles or raw devices. So by default since 10gR1 up to today, we do not interact differently with ASM managed block devices than we did before with a datafile being mapped to a raw device. All of this is without ASMLib, so ignore that one for now. Standard Oracle on any platform that we support (Linux, Windows, Solaris, AIX, ...) does it the exact same way. You start an ASM instance, it handles storage management, all the database instances use and open that storage and read/write from/to it. There are no extra pieces of software needed, including on Linux. ASM is fully functional and selfcontained without any other components. In order for the admin to provide a raw device to ASM or to the database, it has to have persistent device naming. If you booted up a server where a raw disk was named /dev/sdf and you give it to ASM (or even just creating a tablespace without asm on that device with datafile '/dev/sdf') and next time you boot up and that device is now /dev/sdg, you end up with an error. Just like you can't just change datafile names, you can't change device filenames without telling the database, or ASM. persistent device naming on Linux, especially back in those days ways to say it bluntly, a nightmare. In fact there were a number of issues (dating back to 2004) : Linux async IO wasn't pretty persistent device naming including permissions (had to be owned by oracle and the dba group) was very, very difficult to manage system resource usage in terms of open file descriptors So given the above, we tried to find a way to make this easier on the admins, in many ways, similar to why we started working on OCFS a few years earlier - how can we make life easier for the admins on Linux. A feature of Oracle ASM is the ability for third parties to write an extension using what's called ASMLib. It is possible for any third party OS or storage vendor to write a library using a specific Oracle defined interface that gets used by the ASM instance and by the database instance when available. This interface offered 2 components : Define an IO interface - allow any IO to the devices to go through ASMLib Define device discovery - implement an external way of discovering, labeling devices to provide to ASM and the Oracle database instance This is similar to a library that a number of companies have implemented over many years called libODM (Oracle Disk Manager). ODM was specified many years before we introduced ASM and allowed third party vendors to implement their own IO routines so that the database would use this library if installed and make use of the library open/read/write/close,.. routines instead of the standard OS interfaces. PolyServe back in the day used this to optimize their storage solution, Veritas used (and I believe still uses) this for their filesystem. It basically allowed, in particular, filesystem vendors to write libraries that could optimize access to their storage or filesystem.. so ASMLib was not something new, it was basically based on the same model. You have libodm for just database access, you have libasm for asm/database access. Since this library interface existed, we decided to do a reference implementation on Linux. We wrote an ASMLib for Linux that could be used on any Linux platform and other vendors could see how this worked and potentially implement their own solution. As I mentioned earlier, ASMLib and ODMLib are libraries for third party extensions. ASMLib for Linux, since it was a reference implementation implemented both interfaces, the storage discovery part and the IO part. There are 2 components : Oracle ASMLib - the userspace library with config tools (a shared object and some scripts) oracleasm.ko - a kernel module that implements the asm device for /dev/oracleasm/* The userspace library is a binary-only module since it links with and contains Oracle header files but is generic, we only have one asm library for the various Linux platforms. This library is opened by Oracle ASM and by Oracle database processes and this library interacts with the OS through the asm device (/dev/asm). It can install on Oracle Linux, on SuSE SLES, on Red Hat RHEL,.. The library itself doesn't actually care much about the OS version, the kernel module and device cares. The support tools are simple scripts that allow the admin to label devices and scan for disks and devices. This way you can say create an ASM disk label foo on, currently /dev/sdf... So if /dev/sdf disappears and next time is /dev/sdg, we just scan for the label foo and we discover it as /dev/sdg and life goes on without any worry. Also, when the database needs access to the device, we don't have to worry about file permissions or anything it will be taken care of. So it's a convenience thing. The kernel module oracleasm.ko is a Linux kernel module/device driver. It implements a device /dev/oracleasm/* and any and all IO goes through ASMLib - /dev/oracleasm. This kernel module is obviously a very specific Oracle related device driver but it was released under the GPL v2 so anyone could easily build it for their Linux distribution kernels. Advantages for using ASMLib : A good async IO interface for the database, the entire IO interface is based on an optimal ASYNC model for performance A single file descriptor per Oracle process, not one per device or datafile per process reducing # of open filehandles overhead Device scanning and labeling built-in so you do not have to worry about messing with udev or devlabel, permissions or the likes which can be very complex and error prone. Just like with OCFS and OCFS2, each kernel version (major or minor) has to get a new version of the device drivers. We started out building the oracleasm kernel module rpms for many distributions, SLES (in fact in the early days still even for this thing called United Linux) and RHEL. The driver didn't make sense to get pushed into upstream Linux because it's unique and specific to the Oracle database. As it takes a huge effort in terms of build infrastructure and QA and release management to build kernel modules for every architecture, every linux distribution and every major and minor version we worked with the vendors to get them to add this tiny kernel module to their infrastructure. (60k source code file). The folks at SuSE understood this was good for them and their customers and us and added it to SLES. So every build coming from SuSE for SLES contains the oracleasm.ko module. We weren't as successful with other vendors so for quite some time we continued to build it for RHEL and of course as we introduced Oracle Linux end of 2006 also for Oracle Linux. With Oracle Linux it became easy for us because we just added the code to our build system and as we churned out Oracle Linux kernels whether it was for a public release or for customers that needed a one off fix where they also used asmlib, we didn't have to do any extra work it was just all nicely integrated. With the introduction of Oracle Linux's Unbreakable Enterprise Kernel and our interest in being able to exploit ASMLib more, we started working on a very exciting project called Data Integrity. Oracle (Martin Petersen in particular) worked for many years with the T10 standards committee and storage vendors and implemented Linux kernel support for DIF/DIX, data protection in the Linux kernel, note to those that wonder, yes it's all in mainline Linux and under the GPL. This basically gave us all the features in the Linux kernel to checksum a data block, send it to the storage adapter, which can then validate that block and checksum in firmware before it sends it over the wire to the storage array, which can then do another checksum and to the actual DISK which does a final validation before writing the block to the physical media. So what was missing was the ability for a userspace application (read: Oracle RDBMS) to write a block which then has a checksum and validation all the way down to the disk. application to disk. Because we have ASMLib we had an entry into the Linux kernel and Martin added support in ASMLib (kernel driver + userspace) for this functionality. Now, this is all based on relatively current Linux kernels, the oracleasm kernel module depends on the main kernel to have support for it so we can make use of it. Thanks to UEK and us having the ability to ship a more modern, current version of the Linux kernel we were able to introduce this feature into ASMLib for Linux from Oracle. This combined with the fact that we build the asm kernel module when we build every single UEK kernel allowed us to continue improving ASMLib and provide it to our customers. So today, we (Oracle) provide Oracle ASMLib for Oracle Linux and in particular on the Unbreakable Enterprise Kernel. We did the build/testing/delivery of ASMLib for RHEL until RHEL5 but since RHEL6 decided that it was too much effort for us to also maintain all the build and test environments for RHEL and we did not have the ability to use the latest kernel features to introduce the Data Integrity features and we didn't want to end up with multiple versions of asmlib as maintained by us. SuSE SLES still builds and comes with the oracleasm module and they do all the work and RHAT it certainly welcome to do the same. They don't have to rebuild the userspace library, it's really about the kernel module. And finally to re-iterate a few important things : Oracle ASM does not in any way require ASMLib to function completely. ASMlib is a small set of extensions, in particular to make device management easier but there are no extra features exposed through Oracle ASM with ASMLib enabled or disabled. Often customers confuse ASMLib with ASM. again, ASM exists on every Oracle supported OS and on every supported Linux OS, SLES, RHEL, OL withoutASMLib Oracle ASMLib userspace is available for OTN and the kernel module is shipped along with OL/UEK for every build and by SuSE for SLES for every of their builds ASMLib kernel module was built by us for RHEL4 and RHEL5 but we do not build it for RHEL6, nor for the OL6 RHCK kernel. Only for UEK ASMLib for Linux is/was a reference implementation for any third party vendor to be able to offer, if they want to, their own version for their own OS or storage ASMLib as provided by Oracle for Linux continues to be enhanced and evolve and for the kernel module we use UEK as the base OS kernel hope this helps.

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  • Why does only "network" appear in Startup Disks on my Mac?

    - by nbolton
    I have a Linux dual boot setup with my Mac (with Leopard). When I open System Preferences Startup Disk I only see "Network Startup" and no HDD or BOOTCAMP as expected. So now, annoyingly, because "Network Startup" is the only option, it tries to start using the network (the flashing globe) for a short while rather than booting directly into Mac OS X. Is there a way to either fix Startup Disk or manually hack this?

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  • How do I add a broadcast IP to the loopback interface under os/x using ifconfig when my machine has no network?

    - by bandodeotarios
    I'm new to advanced network administration and I would like to do some testing with UDP broadcasting, so I need a broadcast address on my loopback interface. The machine is offline, in other words, there is no network. How can I accomplish that through ifconfig without having to buy a switch as one user in the comments suggested. In Linux all i have to do is use 127.255.255.255 and broadcasts work fine without any network or any switch. If I have a network i can just use 255.255.255.255, obviously.

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  • Should I remove all unmanged switches from my network?

    - by IMAbev
    I have a office network with approx 150 devices (computers/printers/ip phones). Almost all of the end point devices have straight run Cat5e from my Hp switches directly to the device. IP phones for each end user sit between the hp switch and computer. (hp switch - in to phone out of phone in to computer) While I have gotten rid of most of them, I still have a couple linksys unmanaged switches that split off to 2 or more devices. I have heard various reasons for removing these switches but not entirely sure if it actually degrades the network. I agree that eliminating these switches certainly cleans up the network from a management standpoint. Are these unmanaged switches bad for my network? Is there a clear advantage to having 'home run' cable runs to each of my end point devices?

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  • How do I protect a low budget network from rogue DHCP servers?

    - by Kenned
    I am helping a friend manage a shared internet connection in an apartment buildling with 80 apartments - 8 stairways with 10 apartments in each. The network is laid out with the internet router at one end of the building, connected to a cheap non-managed 16 port switch in the first stairway where the first 10 apartments are also connected. One port is connected to another 16 port cheapo switch in the next stairway, where those 10 apartments are connected, and so forth. Sort of a daisy chain of switches, with 10 apartments as spokes on each "daisy". The building is a U-shape, approximately 50 x 50 meters, 20 meters high - so from the router to the farthest apartment it’s probably around 200 meters including up-and-down stairways. We have a fair bit of problems with people hooking up wifi-routers the wrong way, creating rogue DHCP servers which interrupt large groups of the users and we wish to solve this problem by making the network smarter (instead of doing a physical unplugging binary search). With my limited networking skills, I see two ways - DHCP-snooping or splitting the entire network into separate VLANS for each apartment. Separate VLANS gives each apartment their own private connection to the router, while DHCP snooping will still allow LAN gaming and file sharing. Will DHCP snooping work with this kind of network topology, or does that rely on the network being in a proper hub-and-spoke-configuration? I am not sure if there are different levels of DHCP snooping - say like expensive Cisco switches will do anything, but inexpensive ones like TP-Link, D-Link or Netgear will only do it in certain topologies? And will basic VLAN support be good enough for this topology? I guess even cheap managed switches can tag traffic from each port with it’s own VLAN tag, but when the next switch in the daisy chain receives the packet on it’s “downlink” port, wouldn’t it strip or replace the VLAN tag with it’s own trunk-tag (or whatever the name is for the backbone traffic). Money is tight, and I don’t think we can afford professional grade Cisco (I have been campaigning for this for years), so I’d love some advice on which solution has the best support on low-end network equipment and if there are some specific models that are recommended? For instance low-end HP switches or even budget brands like TP-Link, D-Link etc. If I have overlooked another way to solve this problem it is due to my lack of knowledge. :)

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  • Why does a wired network slow down with user increase?

    - by Ed Briscoe
    If you had a wired network, 20 PCs hooked up to a 100 Mbit/sec switch (same onboard ethernet port speed) and you were just sending some test data round. What is the technical explanation as to why 20 machines sending test data around this network to each other is slower than one to one? I mean I know a busy network means it's slower but I'm really trying to understand some more technical details. Thanks for any help

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  • Esx servers in a DMZ

    - by James
    I have two ESX 3.5 servers in a DMZ. I can access these servers on any port from my lan via a VPN. Servers in the DMZ are unable to initiate connections back to the lan, for obvious reasons. I have a vCenter server on my lan and can initially connect to the esx servers fine. However the esx servers then try to send a hearth beat back to the vCenter server on udp/902 obviously this will not get back to the vCenter server, which then marks the ESX servers as not responding and disconnects. There are two broad solutions I can think of; 1) Try to tell vCenter to ignore not getting heart beats. The best I can do here is delay the disconnect by 3 mins. 2) Try some clever network solution. However again I am at loss. Note: The vCenter server is on a lan, and cannot be given a public IP, so firewall rules back will not work. And also I cannot setup a VPN from the DMZ to the lan. **I am adding the following, explanation that I added to the comments Ok maybe this is the bit that I not explaining well. The DMZ is on a remote site, an entirely independent network (network 1). The vCenter server is on our office lan (network 2). Network 2 can connect to any machine on any port on network 1. But network 1 is not allowed to initiate a connection to network 2. Any traffic destined to network 2 from network 1 gets dropped by the firewall as it is traffic to a non-routable address. The only solution I can think of is setting up a VPN from network 1 to network 2, but this is not acceptable So any clever folk out there any ideas? J

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  • samba share not on network after upgrading to Ubuntu 12.04LTS. [migrated]

    - by Sylvain Huard
    I just upgraded an old Ubuntu box to 12.04LTS (machine named A-Ubuntu). This is an upgrade not a format re-install. All the accounts and config were preserved. The basic setup is a local network with 2 Ubuntu machines (let say A-Ubuntu, B-Ubuntu) and a MAC (C-MAC). Before the upgrade, all of them could see each other by their names not only the IP address. The local network has a D-Link Router where everybody is connected with RJ-45 wired etherenet (not wi-fi). Since the A-Ubuntu upgrade, we can't see this machine name on the Network and its name is not on machine list in the D-Link router anymore. We can see it's IP address only. I can't access A-Ubuntu from the other two by its name but I can ping it with its address (192.168.0.109). From A-Ubuntu, I can connect and see the shared samba folders on B-Ubuntu and C-MAC. But from B-Ubuntu and C-MAc, I can't connect to A-Ubuntu. Correct me if I'm wrong but this tells me that Samba should be fine and the real problem is that A-Ubuntu does not advertise its name on the Network so the D-Link does not have it in its table so nobody else finds it. After a lot of googling, I see that it is the job of avahi and mdns to do so. Those packages are running, I checked multiple config files for samba, avahi, mdns to see as if it is like the examples on the WEB and also similar to what I find on the working B-Ubuntu machine. This is the same. I did multiple service restart with samba, avahi, remove the firewall to make sure it does not block the hostname broadcast. I rebooted multiple time to make sure the update I was making were effective. Still, Can't see the A-Ubuntu name on the network. Any idea what it can be?, Where to look next?

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  • If a managed network switch were to overheat, would you consider it no longer reliable?

    - by Scott Szretter
    Here is the scenario - I have a network switch, one of several in a stack. It's fan failed. Soon, there were reports of users with network issues. After quickly replacing the fan, the users were fine, network issues were resolved. I assume the unit was overheating, and thus failing somehow. Today someone suggested to me, that I should not assume the unit is 100% reliable anymore. So what do you think, would an overheat condition (less than 1 day with the fan stopped) potentially cause permanent damage that could at some point come to the surface as future network failures/issues? If it matters, we are talking managed switches such as 3Com/HP SuperStack , ProCurve or PWR-Plus.

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  • How to selectively route network traffic through VPN on Mac OSX Leopard?

    - by newtonapple
    I don't want to send all my network traffic down to VPN when I'm connected to my company's network (via VPN) from home. For example, when I'm working from home, I would like to be able to backup my all files to the Time Capsule at home and still be able to access the company's internal network. I'm using Leopard's built-in VPN client. I've tried unchecking "Send all traffic over VPN connection." If I do that I will lose access to my company's internal websites be it via curl or the web browser (though internal IPs are still reachable). It'd be ideal if I can selectively choose a set of IPs or domains to be routed through VPN and keep the rest on my own network. Is this achievable with Leopard's built-in VPN client? If you have any software recommendations, I'd like to hear them as well.

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  • Troubleshooting loss of network connectivity in Windows 2003 - What else to check?

    - by Benny
    We are facing a weird problem in our data center. Our Backup server (running EMC Networker) loses network connection every alternate day around 3:00 AM (Backup schedule starts at midnight). After 2 hours of outage, the network connectivity recovers automatically and back to normal. What we observed: It is unlikely to be network issue, since it is directly connected to server farm switch (layer 2 connection without any intermediate hops). Further, the server is connected to two different switches for Load balancing using Broadcomm Teaming. a) If it were a switch related issue it is unlikely that both the network ports go down, since they are connected to different switch. b) A possibility Vlan wide issue is also ruled out since other devices in the same Vlan are fine. c) Switch interface status is always up. But there are lot of packet drops during the outage period - Can be attributed to high interface utilization of the backup server (near 100%) d) Connectivity is restored without any change on network. Next suspect is resource utilization on Windows server. Both CPU and Memory have rarely exceeded 80%, but NIC card utilization is alarmingly high (near 100%) Not really sure how to investigate this?

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  • How to selectively route network traffic through VPN on Mac OS X Leopard?

    - by newtonapple
    I don't want to send all my network traffic down to VPN when I'm connected to my company's network (via VPN) from home. For example, when I'm working from home, I would like to be able to backup my all files to the Time Capsule at home and still be able to access the company's internal network. I'm using Leopard's built-in VPN client. I've tried unchecking "Send all traffic over VPN connection." If I do that I will lose access to my company's internal websites be it via curl or the web browser (though internal IPs are still reachable). It'd be ideal if I can selectively choose a set of IPs or domains to be routed through VPN and keep the rest on my own network. Is this achievable with Leopard's built-in VPN client? If you have any software recommendations, I'd like to hear them as well.

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