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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Now you and I go to the City Lord s Mansion, and we will talk to City Lord Yan together.However, although they also noticed Lin Haoming, because of the rules, they really did not dare to cross the range of thousands of miles.
In fact, the Xingfakou is one of the main roads of Dizhai City, a crossroad leading to Fang City.The information I got before only knew that this person was related to the new Eastern King.
Although these words were pleasant to hear, Lin Haoming knew that Chang Yuan might have misspoken, but it didn t matter, he smiled and handed the cloth bag he had prepared to the other party through the window.Under the flash of light, a beam of light was cast, and then two figures appeared in the The Natural Sleep Solution: Unlocking Deeper Rest with Magnesium Gummies beam, one of which was naturally Cui Changting himself, and the second Many people also recognized that it was actually Cui Changting who recently valued a person named Qi Jia very highly.
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The voice continued Di Jun is a legendary figure. He is just like you.Now he imitates those magical weapons with the divine pattern soldier map.
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When Yun Jianyue sacrificed the Changxin Palace Lantern, the crescent wheel turned into a beam of moonlight, and chopped at the waist of Jiao Jiao.Since then, everyone around Master knows that this is Master.
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I have a headache, The women around that kid are all monsters.But all these doubts disappeared when they saw a gorgeous carriage.
Pan Qi said bitterly. Lin Haoming also knows that these monster cultivators, at least, don t have so many ghost thoughts compared to human cultivators, otherwise they wouldn t have revealed such a tragic situation at this time, and thinking of such a terrible chance of falling, Lin Haoming also He couldn t help frowning and asked So many high level beings went in, but only a few came out alive.
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In fact, so many years of painful experiences have really smoothed out many of her emotions.It s really a surprise that you haven t found a suitable candidate Lin Haoming said in disbelief.
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Now that you have this Condensed Yuan Pill, your chances of forming a core will naturally increase greatly.Facing this Saintess of the Colorful Spirit Sect, Lin Haoming knew that it was time to make a decision.
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Come on, even if it can t be used as a clone, but when the crisis really comes, these three spiritual infants can also play some unexpected effects.For someone like me, I am afraid it will be very difficult.
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Yes. Su Yan said. Well. I do have this plan recently After this auction is over, I will go there.Not long after, a cliff appeared on the other side, and Lin Haoming also set foot on the ground.
The arrow just now was very accurate, but the arrow was not too short, which made Lin Haoming wonder how such a short and large arrow could shoot such a small force and directly penetrate the monster s head Lin Haoming knew that if there was no one else there, but he also thought that he would take action on whether he was aware of the situation, which made Lin Haoming feel a little relaxed.
I m sorry for you. These children know What will happen, you really have the heart to see you suffer.But Lin Haoming couldn t let it escape, he immediately chased it, and dealt with it just before it was about to get into the woods.
Right now, Her Highness the princess is welcoming Lin Haoming and others as a representative, which makes others feel that this is simply a joke.This was the precursor of the once in a century island change in the Inland Sea.
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Qing s 770,000 small army in Enze County was wiped out.Lin Haoming recovered from the drowsiness at this time, and I felt the breath around me for the first time, only felt that the vitality of the outer world was several times stronger than before, and it was very quiet and serious.
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