How Network Address Translation Works

00:10:05
https://www.youtube.com/watch?v=QBqPzHEDzvo

摘要

TLDRLa vidéo explique le rôle et le fonctionnement de la traduction d'adresses réseau (NAT) dans la gestion des adresses IPv4 limitées. Lors de son introduction dans les années 70, l'IPv4 a été conçue avec 32 bits, permettant environ 4,2 milliards d'adresses IP, suffisantes pour une époque où Internet était réservé aux chercheurs. Aujourd'hui, avec des milliards de personnes et d'appareils connectés, le nombre limité d'adresses IPv4 est problématique. Le NAT résout ce problème en utilisant une adresse IP publique pour plusieurs appareils privés, traduisant les adresses locales en adresses publiques pour la communication Internet. Cela se fait via le routeur, qui modifie les paquets pour sembler provenir de l'adresse IP publique du réseau. La vidéo démontre également comment la transition vers IPv6, offrant un nombre d'adresses quasi illimité, pourrait éliminer le besoin de NAT, bien que cette transition soit lente en raison de la complexité du matériel et des logiciels nécessaires pour le support complet de l'IPv6.

心得

  • 🌐 La NAT permet aux appareils de partager une adresse IP publique pour communiquer sur Internet.
  • 📉 IPv4, avec ses 4.2 milliards d'adresses, est insuffisant pour les besoins actuels.
  • 🔄 Le routeur adapte les paquets pour maintenir la communication entre réseau privé et public.
  • 📱 Adresses privées, comme 192.168, ne sont pas accessibles directement sur Internet.
  • 🔍 La table NAT associe adresses privées et publiques pour le routage des paquets.
  • 💻 Transition vers IPv6 : plus d'adresses et moins de besoin en NAT.
  • ⚙️ IPv6 nécessite un matériel et un logiciel compatibles pour un déploiement global.
  • 🤝 Le passage à IPv6 est progressif en raison des infrastructures IPv4 existantes.
  • 🔑 NAT joue un rôle crucial dans le fonctionnement des réseaux domestiques modernes.
  • 👨‍💻 Comprendre NAT aide à comprendre les limites actuelles de l'Internet.

时间轴

  • 00:00:00 - 00:10:05

    La vidéo continue en expliquant comment NAT fonctionne : lorsqu'un appareil, comme le laptop de Jane, envoie un paquet à travers le routeur domestique vers un serveur web, le routeur modifie l'adresse IP source privée à une adresse publique. Cela permet au serveur de répondre à une adresse qui est accessible. Le routeur maintient une table de transfert NAT pour faire correspondre les paquets entrants aux appareils corrects sur le réseau privé. L'objectif est d'utiliser des adresses IP privées et de gérer les communications avec le monde extérieur via une adresse IP publique partagée. Enfin, il est mentionné que, bien qu'IPv6 offre une quantité énorme d'adresses IP, la transition est lente à cause de l'infrastructure existante qui doit d'abord être mise à jour.

思维导图

Mind Map

常见问题

  • Pourquoi le NAT est-il nécessaire ?

    Le NAT permet de gérer le problème de nombre limité d'adresses IP disponibles avec IPv4 en partageant une adresse IP publique parmi plusieurs appareils privés.

  • Qu'est-ce qu'une adresse IP "privée" ?

    Une adresse IP privée est utilisée au sein de réseaux locaux et n'est pas accessible depuis l'Internet public, tels que les adresses commençant par 192.168 ou 10.

  • Quel est le rôle du routeur dans le NAT ?

    Le routeur modifie l'adresse IP source d'un paquet pour qu'il ait l'air de provenir de l'adresse IP publique du réseau domestique, facilitant la communication avec le web.

  • Combien d'adresses IP fournit IPv4 ?

    IPv4 offre environ 4,2 milliards d'adresses IP.

  • Qu'est-ce qu'IPv6 ?

    IPv6 est la nouvelle version du protocole IP qui offre un nombre presque illimité d'adresses IP, beaucoup plus qu'IPv4.

  • Pourquoi ne sommes-nous pas encore totalement passés à IPv6 ?

    Le passage à IPv6 est complexe car il nécessite que tout l'infrastructure Internet supporte ce protocole, ce qui prend du temps et des ressources.

  • Qu'est-ce qu'une table de transfert NAT ?

    C'est une table utilisée par le routeur pour associer les adresses IP publiques et privées afin de diriger correctement les paquets vers les appareils respectifs.

  • Comment le NAT affecte-t-il la taille des paquets ?

    Le NAT n'affecte pas vraiment la taille des paquets, mais il limite la nécessité d'augmenter la taille en gérant les adresses IP de manière efficace.

  • Quelle est la différence principale entre IPv4 et IPv6 ?

    La principale différence est la quantité d'adresses : IPv6 propose un nombre beaucoup plus grand d'adresses IP que IPv4.

  • Le NAT est-il toujours nécessaire avec IPv6 ?

    Non, avec IPv6, chaque appareil peut potentiellement avoir sa propre adresse publique, supprimant le besoin du NAT.

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  • 00:00:00
    in this video I'll talk about Network
  • 00:00:02
    address translation how it works and why
  • 00:00:05
    we need it but first let's hear a bit of
  • 00:00:08
    backstory where do these little baby IP
  • 00:00:10
    addresses come from
  • 00:00:12
    anyways back in the late' 70s a couple
  • 00:00:15
    of clever researchers were thinking
  • 00:00:17
    about how long IP addresses should be
  • 00:00:20
    why is this important you have to
  • 00:00:22
    consider that in every data packet we
  • 00:00:25
    have to encode the sender IP and the
  • 00:00:27
    receiver IP if we only reserve a few
  • 00:00:30
    bits to encode an IP address we can keep
  • 00:00:33
    packet sizes small however we'll also
  • 00:00:36
    have few IP addresses to hand out to
  • 00:00:38
    people if on the other hand we choose to
  • 00:00:41
    have lots of bits to encode an IP
  • 00:00:43
    address we'll have lots of IP addresses
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    to hand out but will also have huge
  • 00:00:48
    packets which increases the
  • 00:00:50
    communication overhead so as you can see
  • 00:00:53
    there's a bit of a trade-off going on
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    here you can either have small packets
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    or lots of IP addresses
  • 00:01:00
    they ended up deciding that they'd go
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    with 32 bits for an IP address that left
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    them with roughly 4.2 billion IP
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    addresses you have to consider that back
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    then the internet which wasn't even
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    called the internet back then was just a
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    toy for academics it was definitely not
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    meant for regular people like you and me
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    and that's what's known today as IP
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    version 4 now hang on a second let's do
  • 00:01:27
    a bit of math here we have 4.2 2 billion
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    IP addresses to hand out but we also
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    have 7 billion people living on this
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    planet as of
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    2012 and also consider that each of
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    those 7 billion people may want to use
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    multiple devices to access the internet
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    so yeah we have a bit of a problem on
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    our
  • 00:01:50
    hands what are we going to do about this
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    now cuz clearly having only 4.2 billion
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    machines on the internet is not going to
  • 00:01:57
    be an option we have to figure something
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    out and there is a fix but it's as
  • 00:02:04
    you'll see a bit of a workaround let's
  • 00:02:07
    keep it at that there is in fact a way
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    that we can keep using IP version 4 and
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    get more machines onto the internet
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    here's a typical home network setup this
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    is John's laptop this is Jane's laptop
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    and this is Jane's smartphone they're
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    all connected to the home router that
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    home router in its turn is connected to
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    the internet now when you register with
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    your ISP you get to use an IP address
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    that is accessible throughout the
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    internet and that's assigned to your
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    home router so in this case we have
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    12.13.4 15 assigned to the home router
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    this is a public IP address that
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    theoretically anyone on the internet can
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    send packets too our laptops and
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    smartphone also get their own IP address
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    but instead of getting one of those 4.2
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    billion public IP addresses they get a
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    private IP address that private IP
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    address is designed to them by the home
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    router and is not accessible from the
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    internet now if these IP addresses look
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    familiar to you that's probably because
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    they are this is one of two ranges that
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    are reserved for private networks all
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    addresses starting with
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    192.168 are reserved for priv networks
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    as well as all addresses that start with
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    number 10 you can use these IP addresses
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    without having to worry that some random
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    web server already uses that IP address
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    they can because it's specifically
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    reserved for private networks now let's
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    consider the connection from Jane's
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    laptop for a second Jane's laptop has an
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    IP address of
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    192.168.1.3 here's an example scenario
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    where Jane's laptop wants to know what
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    the current weather is in Texas and to
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    get this information it will try to
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    contact the server at 4030
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    do210 to get that information to reach
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    this web server James's laptop will have
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    to go through the home router through
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    the internet and finally then arriving
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    at the web server first Jane's laptop
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    has to send out a packet requesting the
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    information it says what's the the
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    current temperature in San Antonio Texas
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    now the message here isn't really
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    important the web server should know
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    what to do with that and we won't get
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    into that right now but what you should
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    know is that there is a source IP
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    address here with a source port and a
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    destination IP address with a
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    destination port in this case it's Port
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    80 which is frequently used for HTTP
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    traffic now let's send this package on
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    its way shall we
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    when it arrives at the web server the
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    web server will process the incoming
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    request and try to formulate a
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    reply the reply packet will be addressed
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    to the sender but in this case because
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    it was sent from
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    192.168.1.3 it will not be reachable
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    because it's a private IP address so
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    what do we do now let's rewind that tape
  • 00:05:27
    for just a second
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    Jane's laptop sends out a packet
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    requesting the current temperature in
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    San Antonio taxes It Gets Sent along to
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    the home router but instead of sending
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    it right over the Internet the home
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    router does something that's a little
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    bit
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    sneaky when that packet reemerges you'll
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    notice that the source IP address has
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    been changed this is not the only thing
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    that the home router does in addition it
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    also creates an entry in the NAT for
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    forwarding table now we'll talk about
  • 00:06:01
    the net forwarding table again in just a
  • 00:06:03
    second but for now all you have to
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    remember is that this thing allows us to
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    know which packets are to be sent to
  • 00:06:10
    Jane's laptop when they come in and
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    which packets are to be sent to that
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    smartphone or John's laptop moving right
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    along the packet travels over the
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    internet and arrives at the web server
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    the web server will now create a reply
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    packet and will notice that the
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    destination IP address is is no longer
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    private no instead it's sent to the
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    public IP address of our home router on
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    that specific
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    Port now that our home router has
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    received the response it's time for
  • 00:06:47
    another tiny lie it creates a packet
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    that looks as if it was addressed from
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    the web server directly to Jane's laptop
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    which is not what happened but that's
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    all Jane laptop needs to know cuz it it
  • 00:07:01
    doesn't care about how it got there it
  • 00:07:04
    just wants to get the packet and get
  • 00:07:06
    this over with but how does it know
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    where to send that packet it just
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    received the answer is in the natat
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    forwarding table we just received that
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    packet on Port
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    24604 and that means if we look in our
  • 00:07:21
    net forwarding table that we have to
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    change the IP address on the private
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    site to
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    192.168 .13 on that specific Port over
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    there in the forwarding table Jane's
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    laptop receives the packet and the rest
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    is history Jane's laptop doesn't have to
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    care about any of that Gat stuff the
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    home router completely handles it for
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    Jam's laptop and it is completely
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    transparent so Jam's laptop doesn't have
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    to worry about public and private IP
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    addresses no this is something the
  • 00:07:55
    router fixes and Jam's laptop doesn't
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    have to worry about it
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    of course ideally every computer would
  • 00:08:02
    have its own public IP address which is
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    wir slowly but well actually just slowly
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    moving over to IP version 6 remember how
  • 00:08:12
    IP version 4 had 4.2 billion IP
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    addresses at its disposal well IP
  • 00:08:18
    version 6 has a lot more and I do mean a
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    lot seriously try noting 34 and Then
  • 00:08:26
    followed by 37 zos and that's how much
  • 00:08:30
    IPv6 addresses we have approximately
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    that is a lot if we can give every
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    computer its own public IP address we
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    won't be needing Network address
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    translation anymore this means that
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    routers can once again focus on their
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    Core Business which is routing packets
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    not doing awkward Switcheroo
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    tricks now I can hear you saying this is
  • 00:08:55
    nice and all but why haven't we switched
  • 00:08:57
    yet this IP version 4 thing is a mess we
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    only have 4.2 billion IP addresses and
  • 00:09:03
    that is clumsy as hell well it's not
  • 00:09:06
    that simple we have a lot of Internet
  • 00:09:09
    infrastructure that was built up over
  • 00:09:11
    the years and they all work with IP
  • 00:09:13
    version 4 so we have laptops desktops
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    home routers but also stuff on the ISP
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    side and web servers and they all work
  • 00:09:22
    with IP version 4 all these devices need
  • 00:09:26
    to have hardware and software that
  • 00:09:29
    supports IP version 6 before we can
  • 00:09:32
    entirely switch over and that is a huge
  • 00:09:36
    task just to give you an idea the IP
  • 00:09:39
    version 6 standard was finalized in
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    December of 1998 and yet here we are 14
  • 00:09:47
    years later and we're still running on
  • 00:09:49
    IP version 4 you can see how this is one
  • 00:09:52
    hell of a task all righty if there's
  • 00:09:55
    anything you'd like to see explained
  • 00:09:57
    please do let me know in the comments
  • 00:09:59
    below
  • 00:09:59
    thanks for watching and I'll see you
  • 00:10:01
    next time
标签
  • NAT
  • IPv4
  • IPv6
  • adresse IP
  • routeur
  • réseau privé
  • Internet
  • translation d'adresse
  • infrastructure réseau
  • paquets de données