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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In the evening two days ago, it is reasonable to say that after the material exchange, Lin Haoming was going to leave, but after he was about to leave, this Hu Lanfei sent someone to invite him to go.small ship. In fact, when Lin Haoming saw these people for the first time, he hadn t thought about the state of these people for a while.
When the sky was about to turn dark, most of Erzhu s family had been killed, and the few who remained had fled back.You know the ancient devil language, don t you know Huang Lei continued to ask curiously.
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Lin Haoming s heart trembled when he heard this, but he showed a horrified expression on the surface Miss Hu, what are you talking about Don t scare me, Hu Lanfei is dead How is this possible, he
Obviously
Obviously What Hu Lanqian looked at Lin Haoming and asked.That s because the Dragon King has survived the previous disasters.
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Then why do you think you came here Tian Wei asked back.So Lin Haoming asked the people on board to continue picking.
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It is estimated that it will start in the afternoon.When Lin Haoming took the mana fruit directly, he would recover a certain amount of mana.
Before the boat came down, did Lin Haoming go over Instead, he sent Lan Fei to greet him.Everyone here has no bread, and the team leader Not even some other food, such as candy and the like.
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I have a spare here. I will take you to other places later.In the so called prisoner of war camp area, in fact, there is no lounge, it is also a barracks, and there are some equipment for exercise and recreational activities outside.
He is definitely a young man who knows how to fight, and he is ashamed to be raised by Lin Haoming, so I want you to join me.Still sticking to his will, he can be considered a strong general, but his injuries are also serious, so he can t do anything, so Ning Lin, who is only Understanding the Market Demand in his early seventies, has become the main general under his appearance.
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Wei Shun admired. Is he looking at you as a joke Lin Haoming shook his head and said.The two chose to sit in the private room by the side of the road, and ordered a few big dishes.
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Spicy and bold. Looking at Lin Haoming, he also felt a little interested, and couldn t help but asked The Lake Goddess here can Understanding the Market Demand also subdue demons, and she is much more heroic than that in Jingguo.Very wrong. In fact, for Lin Haoming, it was also the first time I was able to sleep relatively peacefully there, and I was always vigilant afterwards.
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As for the monsters, Lin Haoming has not yet done some more detailed investigations.You all know that, even Ye Zi I also know. Lin Haoming said.
The Dai soldiers who had already rushed out ran back into the camp under the order.Don t tell you those things. When you gave him a choice, he was doomed to end today.
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Mrs. Jin saved him and used him to help Lin Jue deal with it.With so many people, there is no room for maneuver, unless he gives up most of them, but it doesn t look like him Even if he really gives up, can he survive in such an environment This is a dead end What if he can beat the opponent How is this possible, Zhenwu, are you Unleashing Relief: A Comprehensive Review of BioLife CBD Gummies for ED Treatment cheating Except for me Did I cheat once when the spirit descended The world you chose is really tricky, but if you lose at that time, won t you deny it Of course not the three of them said together.
Wei Xiao, what did he say Hearing that Shu Yan grabbed Wei Xiao s arms with both hands, and stared at the man tightly.After all, if he is sure about opening the city gate, you plan to trick us into opening the city first.
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In the vortex, the breath was surging, and countless thunder and lightning were shuttled back and forth, as if the heaven and earth were about to Like a big change.With such a result, He Wanfeng naturally agreed on the balance.
The octagonal boat It is still there, but the light of the mask is gradually weakening, and there is only blue sea water left, and there are no seagulls flying nearby.When Lin Haoming said that, he also wrote at the same time Even if you Relief in a Bottle: Unlocking the Power of Blue CBD Gummies for ED are outside, the other party will not be able to hear what you are saying, so deal with it with all your heart.
Upon hearing this, Feng Shijian immediately changed his words and said, Lin Haoming s trip this time is also to treat Xiong Xuzhi, and maybe he can use the kindness of the treatment in exchange for the protection of Chu State.Originally, according to common sense, Lin Haoming was going to visit that Hu Qinghang, but that elder had retreated before leaving the island.
Soon, the entire Dai Guo small army ended up surrendering as an organization.They were the first to come here and have the highest degree of loyalty.
According to your statement, the Dragon King is the ruler of this world Lin Haoming asked.Lin Taiwei said. The two mothers and men could only go outside, because Lin Haoming knew that it was quiet outside now, and a group of people listened to the two people talking in the hall.
Marshal, it s just that they are arguing over there, and you will have a solution at that time.When the morning light first appeared, the whole small sea hadn t become more intense.
He Zhenting finally sighed. He Wanfeng watched her brother leave, and the tears she was holding back just now fell down.Ah Immortal Lin jumped out of the flames, but his face turned pale when he saw the mulberry tree completely burning, and he immediately understood the means of those who controlled those birds.
Looking at the man in his early seventies, wearing a white dress, his appearance is very beautiful, which means that he looks very pure with the white dress, and being able to look outside, Lin Haoming can naturally guess that the man should be It s not Li Shuxian anymore, and the man in charge of the foreign office has no man, Lin Haoming may suspect that you will be as pure as your eyes and appearance.
Lin Haoming sat and waited for a while, and then saw Bao Yu retreating in casual clothes.opposite In this way, it only takes ten or seventy years to gradually erode.
No need. He Wanfeng waved his hand directly. At this time, Wu Niu still took out eight pieces of money and said They have nothing to do with me, we can get as much as we want.Fortunately, there is a map, but the monotonous environment still makes many people feel depressed after a few days.
For this reason, on the second day after Wei Nao awarded the reward, the two parties unexpectedly signed a letter in unison, asking Wei Nao to recall Wei Xiao to the capital.I must be too much. It The Rise of Male Enhancement Supplements: What's Behind Their Surging Popularity? will take half a while. Seeing this, Captain Lin immediately smiled and said Yes, you still There is no enemy, but you don t have a relatively unified enemy, or an object to fight against.
