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• Lenovo W530 microphone problem

  - by user214245

  Lenovo W530 running Xubuntu 13.10 The microphone appears not to be working. 2 tests made one with audacity and a second with skype. In both instances there appears to be no input. 'Input devices' in the volume control module, also 'recording' indicates background static only. I have opened alsamixer and ensured that everything including microphone boost is set to high. I have tried the changes to alsa-base.conf without success.

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• Déploiement d'une instance GNU/Linux Debian 7 sous CloudStack, premier tutoriel d'une série sur Cloudstack

  Bonjour, Citation: CloudStack est un logiciel de cloud computing open source pour la création, la gestion et le déploiement de services de cloud d'infrastructure. Il utilise des hyperviseurs existants tels que KVM, vSphere, XenServer et / XCP pour la virtualisation. En plus de sa propre API, CloudStack prend également en charge les Amazon Web Services. Voici une série de tests effectués par Ikoula sur ce logiciel. Je vous présente ce tutoriel sur Cloudstack:Déploiement d'une instance...

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• Le kit du bon développeur Rails, partie 3. Par l'équipe de Synbioz

  Dernière partie de notre série d'articles sur les gems à connaitre par un développeur Rails. Dans le premier article, nous nous étions attardés sur l'authentification, la recherche et la pagination. Dans la deuxième partie, ce fut au tour de l'internationalisation et de la gestion de fichiers. Dans ce dernier article, les gems concernant les tests et la gestion des tâches annexes seront à leur tour abordées.

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• git workflow for separating commits

  - by gman

  Best practices with git (or any VCS for that matter) is supposed to be to have each commit do the smallest change possible. But, that doesn't match how I work at all. For example I recently I needed to add some code that checked if the version of a plugin to my system matched the versions the system supports. If not print a warning that the plugin probably requires a newer version of the system. While writing that code I decided I wanted the warnings to be colorized. I already had code that colorized error message so I edited that code. That code was in the startup module of one entry to the system. The plugin checking code was in another path that didn't use that entry point so I moved the colorization code into a separate module so both entry points could use it. On top of that, in order to test my plugin checking code works I need to go edit UI/UX code to make sure it tells the user "You need to upgrade". When all is said and done I've edited 10 files, changed dependencies, the 2 entry points are now both dependant on the colorization code, etc etc. Being lazy I'd probably just git add . && git commit -a the whole thing. Spending 10-15 minutes trying to manipulate all those changes into 3 to 6 smaller commits seems frustrating which brings up the question Are there workflows that work for you or that make this process easier? I don't think I can some how magically always modify stuff in the perfect order since I don't know that order until after I start modifying and seeing what comes up. I know I can git add --interactive etc but it seems, at least for me, kind of hard to know what I'm grabbing exactly the correct changes so that each commit is actually going to work. Also, since the changes are sitting in the current directory it doesn't seem like it would be easy to run tests on each commit to make sure it's going to work short of stashing all the changes. And then, if it were to stash and then run the tests, if I missed a few lines or accidentally added a few too many lines I have no idea how I'd easily recover from that. (as in either grab the missing lines from the stash and then put the rest back or take the few extra lines I shouldn't have grabbed and shove them into the stash for the next commit. Thoughts? Suggestions? PS: I hope this is an appropriate question. The help says development methodologies and processes

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• Déploiement et configuration réseau d'une instance CloudStack, deuxième tutoriel d'une série sur Cloudstack

  Bonjour, Citation: CloudStack est un logiciel de cloud computing open source pour la création, la gestion et le déploiement de services de cloud d'infrastructure. Il utilise des hyperviseurs existants tels que KVM, vSphere, XenServer et / XCP pour la virtualisation. En plus de sa propre API, CloudStack prend également en charge les Amazon Web Services. Voici une série de tests effectués par Ikoula sur ce logiciel. Je vous présente ce deuxième tutoriel sur Cloudstack:Déploiement...

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• Unittest test case only touches the file name

  - by Chen OT

  I was told that unittest is fast and the tests which touches DB, across network, and touches FileSystem are not unittest. In one of my testcases, its input are the file names (amount about 300~400) under a specific folder. Although these input are part of file system, the execution time of this test is very fast. Should I moved this test, which is fast but touches file system, to higher level test?

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• Ten Things I Wish I'd Known When I Started Using tSQLt and SQL Test

  The tSQLt framework is a great way of writing unit tests in the same language as the one being tested, but there are some 'Gotchas' that can catch you out. Dave Green lists a few tips he wished he'd read beforehand. Are you sure you can restore your backups? Run full restore + DBCC CHECKDB quickly and easily with SQL Backup Pro's new automated verification. Check for corruption and prepare for when disaster strikes. Try it now.

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• Déploiement et configuration réseau (firewall) d'une instance CloudStack avec Apache préinstallé, troisième tutoriel d'une série sur Cloudstack

  Bonjour, Citation: CloudStack est un logiciel de cloud computing open source pour la création, la gestion et le déploiement de services de cloud d'infrastructure. Il utilise des hyperviseurs existants tels que KVM, vSphere, XenServer et / XCP pour la virtualisation. En plus de sa propre API, CloudStack prend également en charge les Amazon Web Services. Voici une série de tests effectués par Ikoula sur ce logiciel. Je vous présente ce troisième tutoriel sur Cloudstack:Déploiement...

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• Quick introduction to the Web Load Test features of Visual Studio 2010

  any developers are not even aware that you can set up and run some very sophisticated web load tests for an ASP.NET Application right from within Visual Studio. This article provides a quick introduction to the Web Load Test features of Visual Studio 2010.  read moreBy Peter BrombergDid you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Déployer une instance Debian 7 avec un WordPress prêt à l'emploi en quelques secondes avec CloudStack, quatrième tutoriel d'une série sur Cloudstack

  Bonjour, Citation: CloudStack est un logiciel de cloud computing open source pour la création, la gestion et le déploiement de services de cloud d'infrastructure. Il utilise des hyperviseurs existants tels que KVM, vSphere, XenServer et / XCP pour la virtualisation. En plus de sa propre API, CloudStack prend également en charge les Amazon Web Services. Voici une série de tests effectués par Ikoula sur ce logiciel. Je vous présente ce quatrième tutoriel sur Cloudstack:Déployer...

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• Comparing multiple revisions of the same C File

  - by Draineh

  Hi, I just wondered if anyone had any tricks or programs they used when comparing two of the same file but different versions? I appear to have foolishly made a modification at some point today (Went a few hours without running any tests) and it has stopped the whole project working - without throwing up any errors so it must be subtle whatever I have done. I just thought that there must be a program out there that might highlight differences etc. Otherwise, a step by step search might be in order! Thanks

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• Les rumeurs sur le service de streaming musical par abonnement de YouTube se précisent, YouTube Music Key serait facturé à 9,99 dollars par mois

  Les rumeurs sur le service de streaming musical par abonnement de YouTube se précisent, YouTube Music Key serait facturé à 9,99 dollars par mois Depuis quelques mois des rumeurs circulaient sur YouTube et des tests potentiels d'un nouveau service qui facturerait la consommation de musique et clip vidéo sans publicité et octroierait aux abonnés la possibilité de télécharger des chansons dans leurs dispositifs mobiles. Nos confrères d'Android Police ont mené leur petite enquête sur le sujet et...

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• Robohornet : le benchmark de navigateurs qui voit plus loin que JavaScript, critiqué par Mozilla et forké par Microsoft

  Robohornet : le benchmark de navigateurs qui voit plus loin que JavaScript Critiqué par Mozilla et forké par Microsoft Google vient de lancer la version alpha de Robohornet. C'est un outil open source qui regroupe une série de tests de comparaison (benchmarks) entre les navigateurs Web. Sa particularité est qu'il prend en compte en plus de JavaScript et ses différents frameworks populaires, le rendu HTML, les animations CSS et les manipulations DOM. [IMG]http://idelways.developpez.com/news/images/robohornet-logo.gif[/IMG] Logo de RoboHornet Alex Komoroske, ingénieur et responsable du projet Robohornet chez Google...

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• Visual Studio 2013 Preview sort avec .NET 4.5.1 et Team Foundation Server 2013, l'EDI apporte plus de 5 000 nouvelles API

  Visual Studio 2013 Preview sort avec .NET 4.5.1 et Team Foundation Server 2013 l'EDI apporte plus de 5 000 nouvelles APIAprès Windows 8.1 Preview, c'est au tour de l'environnement de développement de Microsoft Visual Studio 2013 de pointer son nez.La build a été l'occasion pour Microsoft de dévoiler la Preview de Visual Studio 2013, de Team Foundation Server 2013 et de .NET 4.5.1Visual Studio 2013 apporte de nouveaux outils de productivité pour le contrôle de version, de profiling, de tests, de collaboration, de contrôles de sources, de gestion du portfolio agile, de suivi du cycle de vie des applications (ALM) et près de 5 000 ...

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• Should debug code be left in place, always, or added only when debugging and removed when the bug has been found?

  - by gablin

  I, for one, only add debug code (such as print statements) when I'm trying to locate a bug. And once I've found it, I remove the debug code (and add a test case which specifically tests for that bug). I feel that it's cluttering the real code and therefore has no place there unless I'm debugging. How do you do it? Do you leave the debug code in place, or remove it when obsolete (which may be difficult to judge when that is)?

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• Is the test, which touches the filenames under directory, a kind of unittest? [on hold]

  - by Chen OT

  I was told that unittest is fast and the tests which touches DB, across network, and touches FileSystem are not unittest. In one of my testcases, its input are the file names (amount about 300~400) under a specific folder. Although these input are part of file system, the execution time of this test is very fast. Should I moved this test, which is fast but touches file system, to higher level test?

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• jQuery UI 1.9 b1 est disponible, cette version intègre trois nouveaux widgets : Menu, Tooltip et Spinner

  jQuery UI 1.9 b1 est disponible Cette version intègre trois nouveaux widgets : Menu, Tooltip et Spinner Annoncée en novembre 2010 et plus officiellement en mars 2011, la refonte complète de jQuery UI est enfin disponible pour vos tests. Comme annoncé lors du démarrage du projet, il s'agit d'une version non rétrocompatible. Cette refonte a nécessité la construction de 8 versions intermédiaires, il y a eu 200 corrections de bugs et 2100 directives de travail. Elle intègre trois nouv...

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• Windows 8 : le Windows Store s'ouvre aux développeurs de 120 pays, la francophonie représentée de manière quasi exhaustive

  Windows Store : Microsoft fait le point sur les licences d'applications tests avant achat, ventes des fonctionnalités, nombre de machines utilisées Mise à jour du 13/03/2012 Le Windows Store a ouvert ses portes depuis quelques semaines et les utilisateurs peuvent déjà profiter gratuitement des premières applications de style Metro présentes sur la galerie. Pour cela, ils doivent disposer d'un compte Microsoft pour se connecter. Le modèle de licence des applications du magasin dont Microsoft vient de faire une description permet d'offrir aux clients l'accès à l'ensemble de leurs applications sur tous leurs appareils Windows 8, l...

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• Google dévoile Octane 2.0, la nouvelle version de son benchmark pour mesurer les performances des moteurs JavaScript

  Google dévoile Octane 2.0 la nouvelle version de benchmark pour mesurer les performances des moteurs JavaScriptGoogle annonce la sortie d'Octane 2.0 son outil de réalisation de banc d'essai pour la mesure des performances des moteurs JavaScript pour les navigateurs web.En plus d'apporter des correctifs pour les bogues des tests GameBoy emulator, Regex, CodeLoad, DeltaBlue et Navier Stroke de la version précédente, Octane 2.0 s'étoffe de quelques petits ajouts. Au rayon nouveauté, on note l'apparition...

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• Trying to find resources to learn how to test software [closed]

  - by Davek804

  First off, yes this is a general question, and I'd be perfectly happy to move this to another portion of SE, but I didn't see a more fitting sub. Basically, I am hoping a more experienced QA tester can come along and really fill in some basics for me. So far, websites seem to be sparse in terms of explaining languages involved, basic practices, etc. So, I'm sorry in advance if this is too general, but towards the end of this post I ask some specific questions if it's just absolutely unacceptable to speak in general terms. I just landed a position as Junior Systems and QA Engineer with a social media startup. Their QA and testing is almost nonexistent, so if I do a good job, I imagine I'll find a lot of bugs and have a secure role in the business. I'm pretty good with the systems aspect of my role, but I need to learn more about the QA and testing aspects. We run hardware that's touchscreen based - the user can use and interact with the devices. So, in terms of my QA role, in the short term, I need to build scripts to test the hardware/software as a 'user' to try to uncover bugs. First off, what language should these scripts be written in? Does anyone have some examples? What about the longer term 'automated testing'? I'm familiar with regression testing as the developer adds in new features, sure, but the 50,000 other types of testing, not so much. Most of our hardware runs dotnet/C# code, with some of the servers running Java - but I don't expect to need to run tests on the Java side at this point. I hope to meet with one developer today and try to get a good idea of the output from the hardware so that I can 'mock' this data that gets sent to servers, to try to bugtest. Eventually, we will be moving the hardware to be closer to where I live and work, so that I can test virtually and on real hardware. So a lot of the bugs we're dealing with now are like this: the Local Server, which kiosks report their data to gets updated from the kiosks, but the remote server does not. Or, vis versa when the user registers on a kiosk, the remote server updates but the local server does not. But yeah, without much more detail, I imagine a lot of this info isn't helpful. I've bought a book "How Google Tests Software", but it's really a book more about 'how their software testing is different from Microsoft'. It doesn't teach how to test so much as why their methods are better. Does anyone have a good book that I can buy? An ebook maybe? My local Barnes and Noble kinda had a terrible selection. I also figure a book from 2005 is not necessarily that good either.

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• The Huge Disaster Within The Linux 2.6.35 Kernel

  <b>Phoronix:</b> "While the 2.6.35 code has not even seen its first release candidate yet, there are some massive performance drops in a variety of different tests that have yet to be corrected and nothing like we have encountered with previous kernel release cycles especially for a regression that has lived now for about one week."

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• Chrome : Google se met au 64 bits sur Windows 7 et 8 et propose une version plus rapide, stable et sécurisée de son navigateur

  Chrome : Google se met au 64 bits sur Windows 7 et 8 et propose une version plus rapide, stable et sécurisée de son navigateur Google vient de publier les versions tests de Chrome destinées aux utilisateurs de Windows 7 et Windows 8 sur le canal réservé aux développeurs ainsi que via Google Chrome Canary afin de « donner une expérience plus rapide et plus sûre de la navigation ». Google a estimé que cette version offrent aux utilisateurs trois principaux avantages : la vitesse puisque le 64-bits...

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• iptables syn flood countermeasure

  - by Penegal

  I'm trying to adjust my iptables firewall to increase the security of my server, and I found something a bit problematic here : I have to set INPUT policy to ACCEPT and, in addition, to have a rule saying iptables -I INPUT -i eth0 -j ACCEPT. Here comes my script (launched manually for tests) : #!/bin/sh IPT=/sbin/iptables echo "Clearing firewall rules" $IPT -F $IPT -Z $IPT -t nat -F $IPT -t nat -Z $IPT -t mangle -F $IPT -t mangle -Z $IPT -X echo "Defining logging policy for dropped packets" $IPT -N LOGDROP $IPT -A LOGDROP -j LOG -m limit --limit 5/min --log-level debug --log-prefix "iptables rejected: " $IPT -A LOGDROP -j DROP echo "Setting firewall policy" $IPT -P INPUT DROP # Deny all incoming connections $IPT -P OUTPUT ACCEPT # Allow all outgoing connections $IPT -P FORWARD DROP # Deny all forwaring echo "Allowing connections from/to lo and incoming connections from eth0" $IPT -I INPUT -i lo -j ACCEPT $IPT -I OUTPUT -o lo -j ACCEPT #$IPT -I INPUT -i eth0 -j ACCEPT echo "Setting SYN flood countermeasures" $IPT -A INPUT -p tcp -i eth0 --syn -m limit --limit 100/second --limit-burst 200 -j LOGDROP echo "Allowing outgoing traffic corresponding to already initiated connections" $IPT -A OUTPUT -p ALL -m state --state ESTABLISHED,RELATED -j ACCEPT echo "Allowing incoming SSH" $IPT -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set --name SSH -j ACCEPT echo "Setting SSH bruteforce attacks countermeasures (deny more than 10 connections every 10 minutes)" $IPT -A INPUT -p tcp --dport 22 -m recent --update --seconds 600 --hitcount 10 --rttl --name SSH -j LOGDROP echo "Allowing incoming traffic for HTTP, SMTP, NTP, PgSQL and SolR" $IPT -A INPUT -p tcp --dport 25 -i eth0 -j ACCEPT $IPT -A INPUT -p tcp --dport 80 -i eth0 -j ACCEPT $IPT -A INPUT -p udp --dport 123 -i eth0 -j ACCEPT $IPT -A INPUT -p tcp --dport 5433 -i eth0.2654 -s 172.16.0.2 -j ACCEPT $IPT -A INPUT -p udp --dport 5433 -i eth0.2654 -s 172.16.0.2 -j ACCEPT $IPT -A INPUT -p tcp --dport 8983 -i eth0.2654 -s 172.16.0.2 -j ACCEPT $IPT -A INPUT -p udp --dport 8983 -i eth0.2654 -s 172.16.0.2 -j ACCEPT echo "Allowing outgoing traffic for ICMP, SSH, whois, SMTP, DNS, HTTP, PgSQL and SolR" $IPT -A OUTPUT -p tcp --dport 22 -j ACCEPT $IPT -A OUTPUT -p tcp --dport 25 -o eth0 -j ACCEPT $IPT -A OUTPUT -p tcp --dport 43 -o eth0 -j ACCEPT $IPT -A OUTPUT -p tcp --dport 53 -o eth0 -j ACCEPT $IPT -A OUTPUT -p udp --dport 53 -o eth0 -j ACCEPT $IPT -A OUTPUT -p tcp --dport 80 -o eth0 -j ACCEPT $IPT -A OUTPUT -p udp --dport 80 -o eth0 -j ACCEPT #$IPT -A OUTPUT -p tcp --dport 5433 -o eth0 -d 176.31.236.101 -j ACCEPT #$IPT -A OUTPUT -p udp --dport 5433 -o eth0 -d 176.31.236.101 -j ACCEPT #$IPT -A OUTPUT -p tcp --dport 8983 -o eth0 -d 176.31.236.101 -j ACCEPT #$IPT -A OUTPUT -p udp --dport 8983 -o eth0 -d 176.31.236.101 -j ACCEPT $IPT -A OUTPUT -p tcp --sport 5433 -o eth0.2654 -j ACCEPT $IPT -A OUTPUT -p udp --sport 5433 -o eth0.2654 -j ACCEPT $IPT -A OUTPUT -p tcp --sport 8983 -o eth0.2654 -j ACCEPT $IPT -A OUTPUT -p udp --sport 8983 -o eth0.2654 -j ACCEPT $IPT -A OUTPUT -p icmp -j ACCEPT echo "Allowing outgoing FTP backup" $IPT -A OUTPUT -p tcp --dport 20:21 -o eth0 -d 91.121.190.78 -j ACCEPT echo "Dropping and logging everything else" $IPT -A INPUT -s 0/0 -j LOGDROP $IPT -A OUTPUT -j LOGDROP $IPT -A FORWARD -j LOGDROP echo "Firewall loaded." echo "Maintaining new rules for 3 minutes for tests" sleep 180 $IPT -nvL echo "Clearing firewall rules" $IPT -F $IPT -Z $IPT -t nat -F $IPT -t nat -Z $IPT -t mangle -F $IPT -t mangle -Z $IPT -X $IPT -P INPUT ACCEPT $IPT -P OUTPUT ACCEPT $IPT -P FORWARD ACCEPT When I launch this script (I only have a SSH access), the shell displays every message up to Maintaining new rules for 3 minutes for tests, the server is unresponsive during the 3 minutes delay and then resume normal operations. The only solution I found until now was to set $IPT -P INPUT ACCEPT and $IPT -I INPUT -i eth0 -j ACCEPT, but this configuration does not protect me of any attack, which is a great shame for a firewall. I suspect that the error comes from my script and not from iptables, but I don't understand what's wrong with my script. Could some do-gooder explain me my error, please? EDIT: here comes the result of iptables -nvL with the "accept all input" ($IPT -P INPUT ACCEPT and $IPT -I INPUT -i eth0 -j ACCEPT) solution : Chain INPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 1 52 ACCEPT all -- eth0 * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 0 0 LOGDROP tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x17/0x02 limit: avg 100/sec burst 200 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 state NEW recent: SET name: SSH side: source 0 0 LOGDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 recent: UPDATE seconds: 600 hit_count: 10 TTL-Match name: SSH side: source 0 0 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 0 0 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 0 0 ACCEPT udp -- eth0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:123 0 0 ACCEPT tcp -- eth0.2654 * 172.16.0.2 0.0.0.0/0 tcp dpt:5433 0 0 ACCEPT udp -- eth0.2654 * 172.16.0.2 0.0.0.0/0 udp dpt:5433 0 0 ACCEPT tcp -- eth0.2654 * 172.16.0.2 0.0.0.0/0 tcp dpt:8983 0 0 ACCEPT udp -- eth0.2654 * 172.16.0.2 0.0.0.0/0 udp dpt:8983 0 0 LOGDROP all -- * * 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 0 0 LOGDROP all -- * * 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 0 0 ACCEPT all -- * lo 0.0.0.0/0 0.0.0.0/0 2 728 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:43 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:53 0 0 ACCEPT udp -- * eth0 0.0.0.0/0 0.0.0.0/0 udp dpt:53 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 0 0 ACCEPT udp -- * eth0 0.0.0.0/0 0.0.0.0/0 udp dpt:80 0 0 ACCEPT tcp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 tcp spt:5433 0 0 ACCEPT udp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 udp spt:5433 0 0 ACCEPT tcp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 tcp spt:8983 0 0 ACCEPT udp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 udp spt:8983 0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 91.121.190.78 tcp dpts:20:21 0 0 LOGDROP all -- * * 0.0.0.0/0 0.0.0.0/0 Chain LOGDROP (5 references) pkts bytes target prot opt in out source destination 0 0 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 5/min burst 5 LOG flags 0 level 7 prefix `iptables rejected: ' 0 0 DROP all -- * * 0.0.0.0/0 0.0.0.0/0 EDIT #2 : I modified my script (policy ACCEPT, defining authorized incoming packets then logging and dropping everything else) to write iptables -nvL results to a file and to allow only 10 ICMP requests per second, logging and dropping everything else. The result proved unexpected : while the server was unavailable to SSH connections, even already established, I ping-flooded it from another server, and the ping rate was restricted to 10 requests per second. During this test, I also tried to open new SSH connections, which remained unanswered until the script flushed rules. Here comes the iptables stats written after these tests : Chain INPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 600 35520 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0 6 360 LOGDROP tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x17/0x02 limit: avg 100/sec burst 200 0 0 LOGDROP tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 STRING match "w00tw00t.at.ISC.SANS." ALGO name bm TO 65535 0 0 LOGDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 STRING match "Host: anoticiapb.com.br" ALGO name bm TO 65535 0 0 LOGDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 STRING match "Host: www.anoticiapb.com.br" ALGO name bm TO 65535 105 8820 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 10/sec burst 5 830 69720 LOGDROP icmp -- * * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 state NEW recent: SET name: SSH side: source 0 0 LOGDROP tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 recent: UPDATE seconds: 600 hit_count: 10 TTL-Match name: SSH side: source 0 0 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 0 0 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 0 0 ACCEPT udp -- eth0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:80 0 0 ACCEPT udp -- eth0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:123 0 0 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 0 0 ACCEPT tcp -- eth0.2654 * 172.16.0.1 0.0.0.0/0 tcp spt:5433 0 0 ACCEPT udp -- eth0.2654 * 172.16.0.1 0.0.0.0/0 udp spt:5433 0 0 ACCEPT tcp -- eth0.2654 * 172.16.0.1 0.0.0.0/0 tcp spt:8983 0 0 ACCEPT udp -- eth0.2654 * 172.16.0.1 0.0.0.0/0 udp spt:8983 16 1684 LOGDROP all -- * * 0.0.0.0/0 0.0.0.0/0 Chain FORWARD (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 0 0 LOGDROP all -- * * 0.0.0.0/0 0.0.0.0/0 Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes) pkts bytes target prot opt in out source destination 600 35520 ACCEPT all -- * lo 0.0.0.0/0 0.0.0.0/0 0 0 LOGDROP tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 owner UID match 33 0 0 LOGDROP udp -- * eth0 0.0.0.0/0 0.0.0.0/0 udp dpt:80 owner UID match 33 116 11136 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED 0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:25 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:53 0 0 ACCEPT udp -- * eth0 0.0.0.0/0 0.0.0.0/0 udp dpt:53 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 0 0 ACCEPT udp -- * eth0 0.0.0.0/0 0.0.0.0/0 udp dpt:80 0 0 ACCEPT tcp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 tcp dpt:5433 0 0 ACCEPT udp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 udp dpt:5433 0 0 ACCEPT tcp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 tcp dpt:8983 0 0 ACCEPT udp -- * eth0.2654 0.0.0.0/0 0.0.0.0/0 udp dpt:8983 0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp dpt:43 0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 91.121.190.18 tcp dpts:20:21 7 1249 LOGDROP all -- * * 0.0.0.0/0 0.0.0.0/0 Chain LOGDROP (11 references) pkts bytes target prot opt in out source destination 35 3156 LOG all -- * * 0.0.0.0/0 0.0.0.0/0 limit: avg 1/sec burst 5 LOG flags 0 level 7 prefix `iptables rejected: ' 859 73013 DROP all -- * * 0.0.0.0/0 0.0.0.0/0 Here comes the log content added during this test : Mar 28 09:52:51 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=52 TOS=0x00 PREC=0x00 TTL=51 ID=55666 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:52:51 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=52 TOS=0x00 PREC=0x00 TTL=51 ID=55667 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:52:51 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=64 TOS=0x00 PREC=0x00 TTL=51 ID=55668 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:52:51 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=64 TOS=0x00 PREC=0x00 TTL=51 ID=55669 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:52:52 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=64 TOS=0x00 PREC=0x00 TTL=51 ID=55670 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:52:54 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=64 TOS=0x00 PREC=0x00 TTL=51 ID=55671 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:52:58 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=64 TOS=0x00 PREC=0x00 TTL=51 ID=55672 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:52:59 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=6 Mar 28 09:52:59 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=7 Mar 28 09:52:59 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=8 Mar 28 09:52:59 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=9 Mar 28 09:52:59 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=59 Mar 28 09:53:00 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=152 Mar 28 09:53:01 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=246 Mar 28 09:53:02 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=339 Mar 28 09:53:03 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=432 Mar 28 09:53:04 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=524 Mar 28 09:53:05 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=617 Mar 28 09:53:06 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=711 Mar 28 09:53:07 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=804 Mar 28 09:53:08 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=176.31.236.101 DST=176.31.238.3 LEN=84 TOS=0x00 PREC=0x00 TTL=63 ID=0 DF PROTO=ICMP TYPE=8 CODE=0 ID=7430 SEQ=897 Mar 28 09:53:16 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:c0:62:6b:e3:5c:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=60 TOS=0x00 PREC=0x00 TTL=51 ID=61402 DF PROTO=TCP SPT=57637 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 Mar 28 09:53:19 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:c0:62:6b:e3:5c:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=60 TOS=0x00 PREC=0x00 TTL=51 ID=61403 DF PROTO=TCP SPT=57637 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 Mar 28 09:53:21 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=64 TOS=0x00 PREC=0x00 TTL=51 ID=55674 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK URGP=0 Mar 28 09:53:25 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:c0:62:6b:e3:5c:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=60 TOS=0x00 PREC=0x00 TTL=51 ID=61404 DF PROTO=TCP SPT=57637 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 Mar 28 09:53:37 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=116 TOS=0x00 PREC=0x00 TTL=51 ID=55675 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK PSH URGP=0 Mar 28 09:53:37 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=116 TOS=0x00 PREC=0x00 TTL=51 ID=55676 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK PSH URGP=0 Mar 28 09:53:37 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=180 TOS=0x00 PREC=0x00 TTL=51 ID=55677 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK PSH URGP=0 Mar 28 09:53:38 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=180 TOS=0x00 PREC=0x00 TTL=51 ID=55678 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK PSH URGP=0 Mar 28 09:53:39 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=180 TOS=0x00 PREC=0x00 TTL=51 ID=55679 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK PSH URGP=0 Mar 28 09:53:39 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:c0:62:6b:e3:5c:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=60 TOS=0x00 PREC=0x00 TTL=51 ID=5055 DF PROTO=TCP SPT=57638 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 Mar 28 09:53:41 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=180 TOS=0x00 PREC=0x00 TTL=51 ID=55680 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK PSH URGP=0 Mar 28 09:53:42 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:c0:62:6b:e3:5c:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=60 TOS=0x00 PREC=0x00 TTL=51 ID=5056 DF PROTO=TCP SPT=57638 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 Mar 28 09:53:45 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:10:8c:cf:28:39:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=180 TOS=0x00 PREC=0x00 TTL=51 ID=55681 DF PROTO=TCP SPT=57504 DPT=22 WINDOW=501 RES=0x00 ACK PSH URGP=0 Mar 28 09:53:48 localhost kernel: iptables rejected: IN=eth0 OUT= MAC=00:25:90:54:d7:88:c0:62:6b:e3:5c:80:08:00 SRC=194.51.74.245 DST=176.31.238.3 LEN=60 TOS=0x00 PREC=0x00 TTL=51 ID=5057 DF PROTO=TCP SPT=57638 DPT=22 WINDOW=5840 RES=0x00 SYN URGP=0 If I correctly interpreted these results, they say that ICMP rules were correctly interpreted by iptables, but SSH rules were not. This does not make any sense... Does somebody understand where my error comes from? EDIT #3 : After some more tests, I found out that commenting the SYN flood countermeasure removes the problem. I continue researches in this way but, meanwhile, if somebody sees my anti SYN flood rule error...

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• Big Data – Buzz Words: What is MapReduce – Day 7 of 21

  - by Pinal Dave

  In yesterday’s blog post we learned what is Hadoop. In this article we will take a quick look at one of the four most important buzz words which goes around Big Data – MapReduce. What is MapReduce? MapReduce was designed by Google as a programming model for processing large data sets with a parallel, distributed algorithm on a cluster. Though, MapReduce was originally Google proprietary technology, it has been quite a generalized term in the recent time. MapReduce comprises a Map() and Reduce() procedures. Procedure Map() performance filtering and sorting operation on data where as procedure Reduce() performs a summary operation of the data. This model is based on modified concepts of the map and reduce functions commonly available in functional programing. The library where procedure Map() and Reduce() belongs is written in many different languages. The most popular free implementation of MapReduce is Apache Hadoop which we will explore tomorrow. Advantages of MapReduce Procedures The MapReduce Framework usually contains distributed servers and it runs various tasks in parallel to each other. There are various components which manages the communications between various nodes of the data and provides the high availability and fault tolerance. Programs written in MapReduce functional styles are automatically parallelized and executed on commodity machines. The MapReduce Framework takes care of the details of partitioning the data and executing the processes on distributed server on run time. During this process if there is any disaster the framework provides high availability and other available modes take care of the responsibility of the failed node. As you can clearly see more this entire MapReduce Frameworks provides much more than just Map() and Reduce() procedures; it provides scalability and fault tolerance as well. A typical implementation of the MapReduce Framework processes many petabytes of data and thousands of the processing machines. How do MapReduce Framework Works? A typical MapReduce Framework contains petabytes of the data and thousands of the nodes. Here is the basic explanation of the MapReduce Procedures which uses this massive commodity of the servers. Map() Procedure There is always a master node in this infrastructure which takes an input. Right after taking input master node divides it into smaller sub-inputs or sub-problems. These sub-problems are distributed to worker nodes. A worker node later processes them and does necessary analysis. Once the worker node completes the process with this sub-problem it returns it back to master node. Reduce() Procedure All the worker nodes return the answer to the sub-problem assigned to them to master node. The master node collects the answer and once again aggregate that in the form of the answer to the original big problem which was assigned master node. The MapReduce Framework does the above Map () and Reduce () procedure in the parallel and independent to each other. All the Map() procedures can run parallel to each other and once each worker node had completed their task they can send it back to master code to compile it with a single answer. This particular procedure can be very effective when it is implemented on a very large amount of data (Big Data). The MapReduce Framework has five different steps: Preparing Map() Input Executing User Provided Map() Code Shuffle Map Output to Reduce Processor Executing User Provided Reduce Code Producing the Final Output Here is the Dataflow of MapReduce Framework: Input Reader Map Function Partition Function Compare Function Reduce Function Output Writer In a future blog post of this 31 day series we will explore various components of MapReduce in Detail. MapReduce in a Single Statement MapReduce is equivalent to SELECT and GROUP BY of a relational database for a very large database. Tomorrow In tomorrow’s blog post we will discuss Buzz Word – HDFS. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Big Data, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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• OSI Model

  - by kaleidoscope

  The Open System Interconnection Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer network protocol design. In its most basic form, it divides network architecture into seven layers which, from top to bottom, are the Application, Presentation, Session, Transport, Network, Data Link, and Physical Layers. It is therefore often referred to as the OSI Seven Layer Model. A layer is a collection of conceptually similar functions that provide services to the layer above it and receives service from the layer below it. Description of OSI layers: Layer 1: Physical Layer ·         Defines the electrical and physical specifications for devices. In particular, it defines the relationship between a device and a physical medium. ·         Establishment and termination of a connection to a communications medium. ·         Participation in the process whereby the communication resources are effectively shared among multiple users. ·         Modulation or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. Layer 2: Data Link Layer ·         Provides the functional and procedural means to transfer data between network entities. ·         Detect and possibly correct errors that may occur in the Physical Layer. The error check is performed using Frame Check Sequence (FCS). ·         Addresses is then sought to see if it needs to process the rest of the frame itself or whether to pass it on to another host. ·         The Layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. ·         MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. ·         LLC layer controls frame synchronization, flow control and error checking.   Layer 3: Network Layer ·         Provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks. ·         Performs network routing functions, and might also perform fragmentation and reassembly, and report delivery errors. ·         Network Layer Routers operate at this layer—sending data throughout the extended network and making the Internet possible.   Layer 4: Transport Layer ·         Provides transparent transfer of data between end users, providing reliable data transfer services to the upper layers. ·         Controls the reliability of a given link through flow control, segmentation/de-segmentation, and error control. ·         Transport Layer can keep track of the segments and retransmit those that fail. Layer 5: Session Layer ·         Controls the dialogues (connections) between computers. ·         Establishes, manages and terminates the connections between the local and remote application. ·         Provides for full-duplex, half-duplex, or simplex operation, and establishes checkpointing, adjournment, termination, and restart procedures. ·         Implemented explicitly in application environments that use remote procedure calls. Layer 6: Presentation Layer ·         Establishes a context between Application Layer entities, in which the higher-layer entities can use different syntax and semantics, as long as the presentation service understands both and the mapping between them. The presentation service data units are then encapsulated into Session Protocol data units, and moved down the stack. ·         Provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer. Layer 7: Application Layer ·         This layer interacts with software applications that implement a communicating component. ·         Identifies communication partners, determines resource availability, and synchronizes communication. o       When identifying communication partners, the application layer determines the identity and availability of communication partners for an application with data to transmit. o       When determining resource availability, the application layer must decide whether sufficient network or the requested communication exists. o       In synchronizing communication, all communication between applications requires cooperation that is managed by the application layer. Technorati Tags: Kunal,OSI,Networking

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