C’est quoi un serveur DNS et quel en est son rôle ?
Nous allons aborder ici un serveur dont le rôle est essentiel dans Internet, je veux parler bien évidemment du serveur DNS. Vous verrez qu’il est utilisé partout sans forcément que vous vous en rendiez compte.Comme d’habitude pas de termes trop compliqués, je vais vous donner une définition du DNS expliquée de façon simple et répondre aux questions : « C’est quoi un serveur DNS et quel est son rôle ? ». Et pour terminer, nous aborderons également le lien avec le domaine.
Définition et rôle du DNS
Tout d’abord : DNS veut dire « Domain Name System » ou système de nom de domaine. Je vais tout d’abord vous expliquer le fonctionnement, puis nous aborderons la notion de nom de domaine (ou de sous-domaine).
Pour vous expliquer, le rôle et le fonctionnement d’un serveur DNS, je vais reprendre l’exemple du téléphone.
Vous souhaitez appeler quelqu’un dont vous ne connaissez pas le n° de téléphone ?
Que faites-vous ? ….
…. vous utilisez un annuaire !
Et bien voila, un serveur DNS est un annuaire pour ordinateur. Lorsque vous voulez accéder à un ordinateur dans le réseau, votre ordinateur va interroger le serveur DNS pour récupérer l’adresse de l’ordinateur que vous voulez joindre. Une fois, que votre ordinateur aura récupéré l’adresse du destinataire, il pourra le joindre directement avec son adresse IP.
Le serveur DNS va permettre de faire la relation entre nom d’ordinateur et adresse IP. (ramené au téléphone, on obtient : nom de l’abonné et n°).
Vous allez me dire :
» mais je ne cherche jamais à joindre un ordinateur dans le réseau ! «
A quoi, je vais vous répondre :
» bien sur que si ! «
» Actuellement vous lisez ces lignes qui ne sont stockés pas sur votre ordinateur, donc votre ordinateur s’est connecté à un serveur pour récupérer les pages qui sont affichées sur votre écran. «
Exemple
Reprenons en modèle ce que vous avez fait pour arriver sur cette page, et regardons comment le serveur DNS est intervenu sans que vous le sachiez.
Vous avez lancé votre navigateur Internet et vous avez « www.google.fr » comme moteur de recherche par défaut. Donc la page google s’est affichée. Voici le mécanisme complet et regardez à quel endroit le serveur DNS est appelé.
Dans l’exemple ci-dessus, on voit que la requête « quelle est l’adresse de www.google.fr » a répondu 74.125.230.248. Cette requête s’appelle une résolution de nom de domaine.
Si l’on poursuit, on peut constater que le serveur DNS n’est utilisé que sur la partie 1-Question et 2-Réponse. Une fois que l’ordinateur a récupéré l’adresse du serveur à joindre, il n’a plus besoin du serveur DNS.
Cette adresse IP n’est pas une adresse au hasard. Elle correspond bien à un des serveurs de Google. (il y en a évidemment un grand nombre). Donc, si dans votre dans la barre d’adresse de votre navigateur, vous tapez : http://74.125.230.248, la page de recherche de Google doit s’afficher.
Attention, cela fonctionne à l’heure ou j’écris ces lignes, mais ce ne sera peut-être pas le cas au moment ou vous les lirez. (le serveur 74.125.230.248 sera peut-être éteint ? ou affecté à de nouvelle tâches ?)
Pour faire le test vous cliquer sur : http://74.125.230.248
NB du 05/01/2016 : Comme je vous le disais au-dessus, l’adresse peut avoir changé, et c’est le cas : Essayez maintenant avec http://74.125.206.94
Et chez moi ?
La plupart des personnes ignorent cette notion est c’est bien compréhensible. Alors comment cela peut-il fonctionner chez moi puisque je n’ai jamais renseigné ces serveurs ?
Les serveurs DNS fonctionnent en cascade. Pour expliquer cela on pourrait dire que lorsque qu’un serveur ne connait pas la réponse, il va demander à son « parent »
Chez vous, le serveur DNS est votre box (sauf si vous avez renseigné autre chose), et si votre box ne sait pas répondre, elle va interroger son parent : le(s) serveur(s) DNS de votre fournisseur d’accès. Cela peut remonter comme ça jusqu’aux serveurs racines. (on va dire pour simplifier que les serveurs DNS racines sont les serveurs de base du système : on ne peut pas remonter plus haut.)
La configuration DNS de votre ordinateur (ou tablette, et tout autre équipement connecté chez vous) est fournie par le serveur DHCP.
Un fichier
Peut-être en entendrez vous parler si vous travaillez dans l’informatique (ou si vous bricolez un peu). Un fichier présent sur la machine peut remplacer les requêtes DNS.
Ce fichier est le fichier « host » (hôte en français). Il va contenir la correspondance entre les adresses demandées et les adresses IP. Sur chaque ligne de ce fichier on va retrouver au début l’adresse IP suivi d’un espace ou d’une tabulation et ensuite du ou des nom(s) correspondant à cette adresse. Exemple : 74.125.230.248 www.google.fr
La sécurité
Parlons juste un peu de sécurité.
Pour bien comprendre de quoi je veux parler, je vais reprendre l’exemple du téléphone :
Imaginez que vous ayez entre les mains un faux annuaire (piraté) ou les numéros de téléphone ne soient pas les bons, et vous renvoie vers des pirates.
Vous ayez besoin d’appeler votre banque : Vous appelez le numéro de téléphone et vous allez forcément tomber sur des pirates (mais vous ne le savez pas).
Au bout du fil, on peut vous demander des informations confidentielles, et vous les donnerez en tout confiance !!!
Il faut bien comprendre que cela peut être pareil avec des serveurs DNS et qu’il existe des virus qui modifie vos paramètres réseaux ou votre fichier « hosts » pour faire pointer les requêtes DNS vers des serveurs pirates.
Une des blagues des administrateurs réseaux est de modifier, au sein de l’entreprise, une des entrées DNS d’un site vers un autre site. (Par exemple : faire pointer Facebook vers le site des Tortues Ninja ! : ainsi chaque fois que quelqu’un voudra aller sur Facebook, il se retrouvera sur le site des Tortues Ninja)
Changer de DNS
Sachez qu’il est tout à fait possible de changer de DNS. Lorsque vous utilisez votre connexion Internet, les adresses des serveurs DNS sont généralement ceux de votre FAI, mais sachez qu’il est possible d’en changer. Vous trouverez ci-dessous des sites proposant des listes de serveurs :
et je peux également vous en donner 2 très connus :
OpenDNS : 208.67.220.222 et 208.67.222.220
Google : 8.8.8.8 et 8.8.4.4
Pourquoi changer de DNS ?
Je vois 2 raisons principales pour changer de DNS :
Si vous avez peur d’être « espionné », (car un serveur DNS) sait exactement quels sites vous consultez, mais il peut également vous renvoyer vers les sites qu’il a choisi.
Si vous trouvez votre accès un peu lent, (car rappelez-vous un serveur DNS est appelé à chaque page consultée) et plus il mettra du temps à répondre, plus la page mettra du temps à s’afficher.
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After listening to Xie Baolin s explanation, Wang Xuexin understood.Li Yunlong sent a telegram to the headquarters, and the chief asked strangely What You are also interested in this matter Li Yunlong secretly glanced at Wang Xuexin and laughed.
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There were more than 30 vehicles, and there were at least 800 or 900 people.As long as there is a little cloud or fog, it is difficult to find.
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But Mao Xiong has no scruples in this regard. Even because the devils have 700,000 troops in the northeast and are preparing to pinch Mao Xiong with Hans, Mao Xiong and the Eighth Route Army have common interests in this regard
Mao Xiong aids the Eighth Route Army with equipment, and the Eighth Route Army uses these equipment to make trouble behind the devils, which means weakening the devils The power makes it impossible to balance.
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You mean, those two ancient bodies I think it should be about the same, after all, there are many unique skills in Zifu, and some people say that no matter how strong they are, they may not be the opponent of Lin Xuan.Lin Xuan stepped out, the aura on his body swept through the nine heavens, his hands formed seals, and blasted forward, the sky and the earth split, and an ancient magic mountain descended from the sky.
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Xiao Jianren went on to say One day before the incident, a colleague happened to catch Master Seven talking with a woman.Is it really necessary to do this We can completely discuss our own issues without conflict.
The people around suddenly felt that this should be the case.In many cases, to judge who is behind the scenes, you only need to see who benefits the most.
Many young disciples around couldn t help but lower their heads desperately not to be seen smiling.
I guess it s probably because it s too far away from here.It was a pity to both Wang Zhihan and Lin Haoming that the three eyed woman After discovering that Lin Haoming was dodging, he ignored Lin Haoming and immediately dodged.
When they arrived at the temple on the top of the mountain, several people did not gather together.Friends don t have these taboos. It s also because we followed the Demon King that we were lucky enough to know these things and went to Wusha Continent once Pan Qi said.
If you miss it, it may be difficult to find it in the human world.Lin Haoming didn t ask, after all, if he really became a foreign monk.
You are Luo Xiyuan suddenly saw someone blocking her way, and she was a Nascent Soul cultivator.Hey, I really didn t expect that someone here would welcome us like this At this moment, Lin Haoming heard Yan Yang s mocking mockery.
You know, although Peach calls her master, she has never spoken in this tone, but this girl can make her become like this.In this way, there is no problem with Lin Haoming s seemingly insignificant request.
The sea monster insects soon arrived above the multicolored flowers, and one of them landed directly on the bud of a flower with petals the size of a palm, while the other circled and danced around the flower.With her presence, this auction can at least increase the income by 3 to 5 When Lin Haoming really returned to the people of Tianmomen, Qin Aorou immediately spoke
Yeah, otherwise I wouldn t have spent so much time asking her for help.
They are very angry and have no spiritual wisdom. Therefore, they are often used to cultivate the fruit of life, but even if they have the previous conditions, It really takes a lot of energy to cultivate it successfully, so even in the upper The Panther Pill: A Holistic Guide to Understanding and Managing This Powerful Herb realm, this thing is very precious, if you use an analogy, it is almost equivalent to the Condensation Pill, which is helpful for advancing Jindan Hearing this, Lin Haoming basically understood.
Under urging, , m
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Needless Zytanz: Unveiling the Mysteries of a Unique Gemstone to say, the possibility of him escaping from this girl s clutches was very slim.He can understand at a glance that this is definitely a teleportation array, an ultra long distance teleportation array.
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The trunks and branches of the big trees are no different from ordinary big trees.Okay, since this is the case, I have other male genitalia enhancement things, so I won t stay any longer, and leave Seeing this, Lin Yan also said goodbye and left.
This space does not change from day to night, the only difference is that the night is a little darker, and the day is a little brighter, but the brightness is still groggy, and Lin Haoming has already spent several days under the pursuit of those desolate beasts.Following the huge figure, it fell towards Conquer Your Workouts: Unveiling the Power of Men's Stamina Tablets the ground, no matter how terrifying this giant bird is.
Seems to be worried too. At this time, the mysterious man restrained his seemingly furious breath, and said softly It s okay.Really Lin Haoming said disapprovingly. Shen Yan completely stuck to Lin Haoming s body, her rosy lips moved close to Lin Haoming s ear, exhaling Ruolan said Of course, if you don t believe me, you can try it now, and I will be yours alone in the future, always A certain one doesn t want to try Lin Haoming suddenly became fierce from being tepid, grabbed Shen Yan s neck, and lifted her up directly.
