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• What is a SIP 'Gateway' and how is different from a SIP Proxy/Registrar?

  - by Shrey

  Recently I started looking at SIP implementation for a future work. I was reading (Googling) about what SIP means and how to go about implementing a end-to-end SIP enabled VoIP network. What I did not get is what use does a SIP Gateway is for? How different is it with respect to SIP proxy servers or a SIP DNS/Locator like server? I understand probably QoS would be one primary factor - like dedicating a set bandwidth for SIP/VoIP specific I/O over a network. Anything else? Can anyone help me with any other hints/pointers? I fully understand that is quite a basic question - but I really couldn't find any text which could clear my doubt about what 'Gateway' would mean in SIP context and what differentiates it from other SIP based network components (like Softphones, Proxies etc). Thanks a lot.

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• Unity falling body pendulum behaviour

  - by user3447980

  I wonder if someone could provide some guidance. Im attempting to create a pendulum like behaviour in 2D space in Unity without using a hinge joint. Essentially I want to affect a falling body to act as though it were restrained at the radius of a point, and to be subject to gravity and friction etc. Ive tried many modifications of this code, and have come up with some cool 'strange-attractor' like behaviour but i cannot for the life of me create a realistic pendulum like action. This is what I have so far: startingposition = transform.position; //Get start position newposition = startingposition + velocity; //add old velocity newposition.y -= gravity * Time.deltaTime; //add gravity newposition = pivot + Vector2.ClampMagnitude(newposition-pivot,radius); //clamp body at radius??? velocity = newposition-startingposition; //Get new velocity transform.Translate (velocity * Time.deltaTime, Space.World); //apply to transform So im working out the new position based on the old velocity + gravity, then constraining it to a distance from a point, which is the element in the code i cannot get correct. Is this a logical way to go about it?

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• Dell EqualLogic vs. EMC VNXe [closed]

  - by Untalented

  We've been looking into SMB SANs and based on the competitive pricing I've been getting we're really liking these two array's. There are some pro's to both solutions, but I've unable to really decide which to choose. The EMC offers better expandability since you can buy an additional shelf (roughly $1200) and can add drives then to the array. However, the Dell unit is still very nice. Can anyone comment on their experiences with the two and thoughts on this? Also, to get the VMware Storage API support you need VMware Enterprise. How much additional performance does this provide? It's roughly $15k more than the Essentials Plus bundle we're looking at (this is a small environment [3 Hosts 1 Array].

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• Routing Essentials

  - by zharvey

  I'm a programmer trying to fill a big hole in my understanding of networking basics. I've been reading a good book (Networking Bible by Sosinki) but I have been finding that there is a lot of "assumed" information contained, where terms/concepts are thrown at the reader without a proper introduction to them. I understand that a "route" is a path through a network. But I am struggling with visualizing some routing-based concepts. Namely: How do routes actually manifest themselves in the hardware? Are they just a list of IP addresses that get computed at the network layer, and then executed by the transport? What kind of data exists in a so-caleld routing table? Is a routing-table just the mechanism for holding these lists of IP address (read above)? What are the performance pros/cons for having a static route, as opposed to a dynamic route?

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• Optimized algorithm for line-sphere intersection in GLSL

  - by fernacolo

  Well, hello then! I need to find intersection between line and sphere in GLSL. Right now my solution is based on Paul Bourke's page and was ported to GLSL this way: // The line passes through p1 and p2: vec3 p1 = (...); vec3 p2 = (...); // Sphere center is p3, radius is r: vec3 p3 = (...); float r = ...; float x1 = p1.x; float y1 = p1.y; float z1 = p1.z; float x2 = p2.x; float y2 = p2.y; float z2 = p2.z; float x3 = p3.x; float y3 = p3.y; float z3 = p3.z; float dx = x2 - x1; float dy = y2 - y1; float dz = z2 - z1; float a = dx*dx + dy*dy + dz*dz; float b = 2.0 * (dx * (x1 - x3) + dy * (y1 - y3) + dz * (z1 - z3)); float c = x3*x3 + y3*y3 + z3*z3 + x1*x1 + y1*y1 + z1*z1 - 2.0 * (x3*x1 + y3*y1 + z3*z1) - r*r; float test = b*b - 4.0*a*c; if (test >= 0.0) { // Hit (according to Treebeard, "a fine hit"). float u = (-b - sqrt(test)) / (2.0 * a); vec3 hitp = p1 + u * (p2 - p1); // Now use hitp. } It works perfectly! But it seems slow... I'm new at GLSL. You can answer this questions in two ways: Tell me there is no solution, showing some proof or strong evidence. Tell me about GLSL features (vector APIs, primitive operations) that makes the above algorithm faster, showing some example. Thanks a lot!

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• Strategy for hosting 700+ domains names, each with a static HTML site

  - by jonschlinkert

  I have a portfolio of more than 700 domain names, and ideally I'd like to put up a single-page HTML/CSS/JavaScript webpage for each domain. Is there a system/strategy/workflow that will allow me to: Automate the deployment of new websites, quickly and easily without having to manually initiate each new website in an admin panel. For instance, I've seen dropbox-based solutions that claim to make it simple to setup new websites on your dropbox account, but you still have to set each one up in an admin interface first. It would be so much easier to have a folder naming convention that allowed the user to easily clone/copy/duplicate sites inside their Dropbox App folder (https://www.dropbox.com/developers/blog/23) to create new ones. Sounds interesting, however... It's easy to manage CNAMEs on the registrar-side, but is there a way to quickly associate CNAMEs with new websites (on the hosting side), maybe using the method offered by gh-pages-style (https://help.github.com/articles/setting-up-a-custom-domain-with-pages)? With GitHub's gh-pages, all you have to do is drop a file called CNAME into your repo, with the domain name you want associated with the repo inside the file. gh-pages isn't a good solution for what I'm doing though unfortunately. I'm also a front-end developer, specializing in rapid web development and "front-end build systems", so I building and maintaining static assets for hundreds of sites is no problem. It's the hosting-side that I really struggle with. Any suggestions?

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• Event notifications for Reporting Systems

  - by Marc Schluper

  The last couple of months I have been working on an application that allows people to browse a data mart. Nice, but nothing new. In this context I have an idea that I want to publish before anyone else patents it: event notifications. You see, reporting systems are not used as much as we’d like. Typically, users don’t know where to look for reports that might interest them. At best, there are some standard reports that people generate every so often, i.e. based on a time trigger. Or some reporting systems can be configured to send monthly reports around, for convenience. But apart from that, the reporting system is just sitting there, waiting for the rare curious user who makes the effort to dig a bit for treasures to be found. Wouldn’t it be great if there were data triggers? Imagine we could configure the reporting system to let us know when something interesting has happened. It would send us a message containing a link that would take us to the relevant section of the reporting system, showing a report with all the data pertaining to that event, preparing us for proper actions. Here in the North West this would really be great. You see, it rains here most of the time from October to June, so why even check the weather forecast? But sometimes, sometimes it snows. And sometimes the sun shines. So rather than me going to the weather site and seeing over and over again that it will be raining, making me think “why bother?” I’d like to configure the weather site so that it lets me know when the rain stops. Now, hopefully nobody has patented this idea already. Let me know.

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• Easiest way to move my Windows installation to an SSD?

  - by Jon Artus

  I've taken the plunge and bought an SSD and want to move my existing Windows installation over. The current hard disk is 500Gb, but I've trimmed the contents down to about ~40Gb. I'm transferring it across to a 100Gb SSD and looking for the easiest way just to copy everything across and set the SSD up as a boot device. I've looked at a few tools like Macrium Reflect, but they don't seem able to restore to a smaller drive. Do I need to go for something like PING to do this? I'm trying to avoid scary Linux-based boot utilities if possible, does anyone know of an easier way?

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• Replacing sick NTP server source and re-synching (with internal time currently 2 minutes late)

  - by l0c0b0x

  One of the external NTP servers (the primary one--currently) we're using as source seems to not be responding to NTP calls. Unfortunately, on our core router (Cisco 6509), the NTP functionality hasn't switched to the secondary NTP external server as it was expected. As a result, our core router which is pretty much our main internal NTP source is 2 minutes late. I'm planning to fix the external router issue by making the external NTP source be the one currently working. I'm wondering, how much will a 2 minute change affect my users and services? Specially since these days, we're heavily relying on certificate-based authentication. We're a Windows/Cisco shop. Internal NTP setup: [Core Router 1 / Cisco 6509]: looking out to two external NTP servers (in which the primary one is not responding to NTP calls) [Core Router 2]: Synching with Core router 1 (primary), working external router (secondary) [Other Cisco network devices]: Synching with Core router 1 (primary), core router 2 (secondary) [Domain controller(s)]: Synching with Core router 1 [All windows clients/servers]: Synching with domain controllers

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• Interpolation between two 3D points?

  - by meds

  I'm working with some splines which define a path a character follows (you can see a gameplay video here to get a better understanding of what's going on: http://www.youtube.com/watch?v=BndobjOiZ6g). Basically the characters 'forward' look direction is set to the 'forward' direction of the spline and when players tilt their phone left and right the character is strafed along its 'right' coordinate. The issue with this is (rather obviously) in performance, interpolating over a spline to find the nearest position and tangent relative to the player is an incredibly costly operation. To get by this I cache a finite number of positions in what I call 'SplineDetails', the class is as follows: public class SplineDetails { public SplineDetails() { Forward = Vector3.forward; Position = Vector3.one * float.MaxValue; Alpha = -1; } public float Alpha; // [0,1] measured along length of spline where 0 is the initial point and 1 is the end point of the spline public Vector3 Position; // the point of the spline at this alpha public Vector3 Forward; // the forward tangent of the spline at this alpha } I populate this with say 30 coordinates and I can give a rough estimate of a coordinate and 'forward' based on a position past in. It's not as accurate but it's much faster. But now I'd like to make the system work better by estimating positions and 'forward' directions by interpolating between two of the cached points though I'm stuck trying to figure out some logic. My first problem is, how can I determine between which two points the object is? Given each point can be placed at different intervals along the spline it could mean that two points in front or behind the object can be closer to the object. The other problem is to figure out the proportion between the two paths it's between, i.e. if there is a point a at coordinate (0,0,0) and point b at coordinate (1,0,0) if the object is at position (0.5,0,0) then the result it should give is '0.5' (as it is equal distance away from point a and point b). That's a simple example, but what if the object is at coordinate (0.5,3,0) for example?

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• Conditional formatting

  - by djerry

  I have a rather annoying format I need to implement. There are 2 cells, both containing a date (cell A and B). B contains a date (24-06-2011). Cell B should be colored if cell A is between a date range, based on cell B. So if cell A lies between cell B - 7 days and cell B - 11 days, then it should be triggered. So with numbers: If B is 24-06-2011 then the range (which is not in any cell in the spreadsheet) is 13-06-2011 until 17-06-2011. If the date in cell A (let's say 14-06-2011) is in that range, cell B should be colored. Any ideas?

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• Introducing Code Map for Visual Studio 2012 September CTP

  - by krislankford

  As part of the Visual Studio 2012 CTP for September, Visual Studio got a little sexier at helping you discover and visualize your code. The introduction of the Code Map feature helps compliment the variety of other tools that are included with Visual Studio to help you analyze and visualize your projects and solutions. Code Map leverages the dgml format within Visual Studio that is currently used b the Architecture and Modeling tools. This is a nice addition that gets us from point A to point B a little faster. The great thing about Code Map is that you can gain access to the functionality from directly within your code from the context menu. This Code Map functionality is also context specific based on your cursor. You can evaluate and add items such as methods and variables directly to the Code Map window. As you add items the Code Map surface is updated to show your new item plus any relationships and dependencies that have been introduced in your code. Something that is also very nice is that the Code Map surface is interactive and allows you to use the F12 button (Go To Definition) which can help you navigate your code especially is you are adding items that span multiple files or projects. To get started all you have to do is go out and download the September CTP for Visual Studio 2012 located here. Happy Coding!   Code Map Window

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• good literature for teaching object oriented thinking in C [closed]

  - by Dipan Mehta

  Quite often C is the primary platform for the development. And when things are large scale, I have seen partitioning of the system as different objects is quite a natural thing. Some or many of the object orientated analysis and design principles are used here very well. This is not a debate question about whether or not C is a good candidate for object oriented programming or not. This is also NOT a question how to do OO in C. You can refer to this question and there are probably many such citations. As far as I am concerned, I have learned some of this things while working with many open source and commercial projects. (libjpeg, ffmpeg, Gstreamer which is based on GObject). I can probably extend a few references that explains some of these concepts such as - 1. Event Helix article, 2. Linux Mag article 3. one of my answers which links Schreiner's reference. Unfortunately, when we induct younger folks, it seems too hard to make them learn all of it the hard way. Usually, when we say it's C, a general reaction is to throw away all of the "Object thinking". Looking for help extending above references from those who have been in the similar areas of work. Are there any good formal literature that explains how Object thinking can be made to use while you are working in C? I have seen tons of book on general "object oriented paradigms" but they all focus on advanced languages mostly not in C. You see most C books - but most focus only on the syntax and the obfuscated corners of C and that's it. There are hardly ANY good reference, specially books or any systematic (I mean formal) literature on how to apply OO in C. This is very surprising given that so many large scale open source projects use C which are truly using this very well; but we hardly see any good formal literature on this subject.

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• How to take a copy of wubi ubuntu system as it is?

  - by rajat

  I have installed ubuntu (as a dual boot) using wubi (Windows-based UBuntu Installer) installer for windows, and have been working in linux since then. Now that I have many projects with many dependencies, I'd want to install the same ubuntu to other machines, so that I don't need to install Ubuntu first, and then each and every project and it's dependencies. There is a folder called ubuntu in my windows drive, which was created by wubi and which contains all the ubuntu stuff. Other machines have only windows 7 installed and have the same configuration. Is there any way to install the save ubuntu I am using to the other machines ?

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• Genetic Algorithm new generation exponentially increasing

  - by Rdz

  I'm programming Genetic Algorithm in C++ and after searching all kind of ways of doing GA'a operators (selection, crossover, mutation) I came up with a doubt. Let's say I have an initial population of 500. My selection will consist in getting the top 20% of 500(based on best fitness). So I get 100 individuals to mate. When I do the crossover I'll get 2 children where both together have 50% of surviving. So far so good. I start the mutation, and everything's ok.. Now when I start choosing the Next generation, I see that I have a big number of children (in this case, 4950 if you wanna know). Now the thing is, every time I run GA, if I send all the children to the next generation, the number of individuals per generation will increase exponentially. So there must be a way of choosing the children to fulfill a new generation without getting out of this range of the initial population. What I'm asking here is if there is anyway of choosing the children to fill the new generations OR should I choose somehow (and maybe reduce) the parents to mate so I don't get so many children in the end. Thanks :)

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• Client-Server MMOG & data structures sync when joining / playing

  - by plang

  After reading a few articles on MMOG architecture, there is still one point on which I cannot find much information: it has to do with how you keep in sync server data on the client, when you join, and while you play. A pretty vague question, I agree. Let me refine it: Let's say we have an MMOG virtual world subdivided into geographical cells. A player in a cell is mostly interested in what happens in the cell itself, and all the surrounding cells, not more. When joining the game for the first time, the only thing we can do is send some sort of "database dump" of the interesting cells to the client. When playing, I guess it would be very inefficient to do the same thing regularly. I imagine the best thing to do is to send "deltas" to the client, which would allow keeping the local database in sync. Now let's say the player moves, and arrives in another cell. Surrounding cells change, and for all the new cells the player subscribes, the same technique as used when joining the game has to be used: some sort of "database dump". This mechanic of joining/moving in a cell-based MMOG virtual world interests me, and I was wondering if there were tried and tested techniques in this domain. Thanks!

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• How (and when) to move users to mysqli and PDO_MYSQL?

  - by cj

  An important discussion on the PHP "internals" development mailing list is taking place. It's one that you should take some note of. It concerns the next step in transitioning PHP applications away from the very old mysql extension and towards adopting the much better mysqli extension or PDO_MYSQL driver for PDO. This would allow the mysql extension to, at some as-yet undetermined time in the future, be removed. Both mysqli and PDO_MYSQL have been around for many years, and have various advantages: http://php.net/manual/en/mysqlinfo.api.choosing.php The initial RFC for this next step is at https://wiki.php.net/rfc/mysql_deprecation I would expect the RFC to change substantially based on current discussion. The crux of that discussion is the timing of the next step of deprecation. There is also discussion of the carrot approach (showing users the benfits of moving), and stick approach (displaying warnings when the mysql extension is used). As always, there is a lot of guesswork going on as to what MySQL APIs are in current use by PHP applications, how those applications are deployed, and what their upgrade cycle is. This is where you can add your weight to the discussion - and also help by spreading the word to move to mysqli or PDO_MYSQL. An example of such a 'carrot' is the excellent summary at Ulf Wendel's blog: http://blog.ulf-wendel.de/2012/php-mysql-why-to-upgrade-extmysql/ I want to repeat that no time frame for the eventual removal of the mysql extension is set. I expect it to be some years away.

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• Time difference between servers after disaster recovery

  - by Sandokan

  We are running an old training system based on Windows Server 2003 and XP-clients. The solution is rather simple with four servers, two of them beeing DC:s. Everything is preconfigured and that goes for backup scheme as well. The backup software is Symantec BackupExec 2010. The scheme is a standard GF-F-S routine with full backups running once a week on Sundays. The other six days run differential backups. Now let's say in a worst case scenario, a server crashes on Saturday and we have to restore it from backup. The last backup will then be six days old and thus it will come online with six days old configurations. Will this pose a problem for the other servers or will the recovered server "get in line" eventually?

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• What would happen if I did a "Boot to VHD" to a VHD that was configured to run under Hyper-V?

  - by tbone

  Microsoft has a Hyper-V based VM I'm interested in running, however, I don't have access to a Windows Server 2008 machine to try it on, only a Windows 7 Pro x64 machine (Windows 7 does not support Hyper-V). This is the VM in question: This download contains three Windows Server 2008 R2 SP1 Hyper-V Virtual Machine set for evaluating and demonstrating Office 2010, SharePoint 2010 and Project Server 2010. 2010 Information Worker Demonstration and Evaluation Virtual Machine (SP1) http://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=27417 I came across a somewhat relevant article from Scott Hanselman: Less Virtual, More Machine - Windows 7 and the magic of Boot to VHD: http://www.hanselman.com/blog/LessVirtualMoreMachineWindows7AndTheMagicOfBootToVHD.aspx I realize other options are to convert this VM to a VMWare compatible VM or some of the options to run it under VirtualBox. But instead of those routes, I'm wondering: What would happen if I tried to go the "Boot to VHD" route using this Hyper-V VHD? Is it possible that during the boot process, Windows would simply notice that hardware had changed and adjust accordingly, installing the appropriate drivers and continuing on without a hitch?

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• What determines which Javascript functions are blocking vs non-blocking?

  - by Sean

  I have been doing web-based Javascript (vanilla JS, jQuery, Backbone, etc.) for a few years now, and recently I've been doing some work with Node.js. It took me a while to get the hang of "non-blocking" programming, but I've now gotten used to using callbacks for IO operations and whatnot. I understand that Javascript is single-threaded by nature. I understand the concept of the Node "event queue". What I DON'T understand is what determines whether an individual javascript operation is "blocking" vs. "non-blocking". How do I know which operations I can depend on to produce an output synchronously for me to use in later code, and which ones I'll need to pass callbacks to so I can process the output after the initial operation has completed? Is there a list of Javascript functions somewhere that are asynchronous/non-blocking, and a list of ones that are synchronous/blocking? What is preventing my Javascript app from being one giant race condition? I know that operations that take a long time, like IO operations in Node and AJAX operations on the web, require them to be asynchronous and therefore use callbacks - but who is determining what qualifies as "a long time"? Is there some sort of trigger within these operations that removes them from the normal "event queue"? If not, what makes them different from simple operations like assigning values to variables or looping through arrays, which it seems we can depend on to finish in a synchronous manner? Perhaps I'm not even thinking of this correctly - hoping someone can set me straight. Thanks!

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• You are or will be a laid off programmer - what do you do a year ago, right now, tomorrow, and next week?

  - by Adam Davis

  Many programmers, software engineers, and other technology professionals are out of work, facing layoffs, or are unprepared for layoffs though they feel secure right now. What should every programmer do right now (even if secure in their current job) to prepare them for layoffs down the road? If your boss came to your cubicle while you read this and laid you off: What would you do immediately after? What would you do tomorrow? What would you do next week? It obvious that one should always have an up to date resume, always get recommendations from people when they see you at your best (not when you're looking for a new job), etc. What are the things, step by step, that every programmer should do (or should consider doing) long before they are laid off, when they're laid off, and shortly after being laid off? This is a question with many possible facets. While I want to encourage discussion to center around programming career based answers, please reconsider before downvoting someone because they're thinking in terms of how they're going to prevent going into debt. Bonus catch-22 type question: You can study a new language or technology while out of work, but most places want you to have more than 1-2 months experience in a working environment, not just from a learning exercise. Is it worthwhile to place a priority on new (ideally in demand) skills, or should you instead hone existing skills?

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• SQL Server plus small files

  - by user1467163

  I have a MSSQL server, 3 volumes, that runs some processes that seem to take way too long. One of these processes reads in a zip file, then writes to a database based on what's in the zip file.... for each record. I have 2 volumes in use and am creating the third- so I am trying to plan how to do this. OS has to remain on vol. 1. The TLogs should probably go on the new volume and the mdf's on the existing vol.2.. Do I put the file store on the volume with the MDF's so they don't interfere with the TLog writes, or with the TLogs so they don't interfere with the TLog flush to the MDFs? I know it's best to have more servers / volumes but I have to make do with whats on hand for now. I appreciate any suggestions.

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• Hash Algorithm Randomness Visualization

  - by clstroud

  I'm curious if anyone here has any idea how the images were generated as shown in this response: Which hashing algorithm is best for uniqueness and speed? Ian posted a very well-received response but I can't seem to understand how he went about making the images. I hate to make a new question dedicated to this, but I can't find any means to ask him more directly. On the other hand, perhaps someone has an alternative perspective. The best I can personally come up with would be to have it almost like a bar graph, which would illustrate how evenly the buckets of the hash table are being generated. I have a working Cocoa program that does this, but it can't generate anything like what he showed there. So the question is two fold I suppose: A) How does one truly interpret the data he shows? Is it more than "less whitespace = better"? B) How does one generate such an image based on some set of inputs, a hash, and an index? Perhaps I'm misunderstanding entirely, but I really would like to know more about this particular visualization technique. Or maybe I'm mis-applying this to hash tables rather than just hashes in general, but in that case I don't know how it would be "bounded" for the image.

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• Why is my ethernet interface in promiscuous mode

  - by nhed

  I read that seeing a flag of M in netstat -i is the way to tell which of your interfaces is in promiscuous mode I run it and I see that eth1 is in promiscuous mode $ netstat -i Kernel Interface table Iface MTU Met RX-OK RX-ERR RX-DRP RX-OVR TX-OK TX-ERR TX-DRP TX-OVR Flg eth1 1500 0 1770161198 0 0 0 57446481 0 0 0 BMRU lo 16436 0 97501566 0 0 0 97501566 0 0 0 LRU This seems to be the case on all the machines I checked (All Centos6.0, both virtual and physical), any idea why ethernet devices would be in such a mode unless someone was running any pcap based app (sudo lsof | grep pcap shows nothing)? I did not see any mention of promiscuous in any of the config files (sudo grep -r promis /etc) Any ideas what puts the interface into that mode and why? p.s. most of the posts I see seem to be security related, this is not that

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• KVM to Xen migration

  - by qweet

  I've recently been appointed to create some VMs for production use, and went gung ho into making a KVM based VM instead of finding out what our production server uses. I've only recently found out though that our own servers use Xensource OS, and don't look like they're going to be upgraded in the near future. So for the moment, I'm stuck with either two choices- attempting to convert the KVM VM into a Xen VM, or rebuilding what I have into a new Xen VM. Being the lazy person I am, I would rather not have to rebuild the VM. I've looked for some documentation on a procedure to do this, but the only thing I can come up with is an ancient article with some vague instructions. So this is my question, Server Fault- can one migrate a KVM running on a KVM kernel to a Xen kernel? And if so, how?

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