Shadowing Practice: Everything You Need to Know About DNS: Crash Course System Design #4 - Learn English Speaking with Video
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DNS or domain name system is the backbone of the internet,
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but few know exactly how it works.
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In this video, we'll learn all about the system design of DNS.
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Let's dive right in.
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DNS is the internet's directory.
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It translates human readable domain names such as google.com to machine readable IP addresses.
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DNS is a little confusing because there are different types of DNS server in the DNS hierarchy,
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each serving a different purpose.
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When a browser makes a DNS query,
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it's asking a DNS resolver.
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Now this DNS resolver could be from our ISP or from popular DNS providers like Cloudflare's 1.1.1.1 or Google's 8.8.8.8.
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If the DNS resolver does not have the answer in its cache,
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it finds the right authoritative nameserver and asks it.
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The authoritative nameserver is the one that holds the answer.
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When we update a domain's DNS records as a site owner,
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we are updating its authoritative nameserver.
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How does the DNS resolver find the authoritative nameserver?
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This is where the system of DNS gets interesting.
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There are three main levels of authoritative DNS servers.
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There are the root name servers,
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the top level domain or TLD name servers,
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and the authoritative name servers for the domains.
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The root name servers store the IP addresses of the TLD name servers.
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There are 13 logical root name servers.
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Each root name server has a single IP address assigned to it.
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There are actually many physical servers behind each IP address.
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Through the magic of Anycast,
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we get routed to the one closest to us.
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The TLD name servers store the IP addresses of the authoritative name servers for all the domains under them.
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There are many types of TLD names.
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We are all familiar with .com, .org, and .edu.
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There are also country code TLDs like .de and .uk.
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There are many others.
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The authoritative nameservers for a domain provide well,
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authoritative answers to DNS queries.
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When we register a domain,
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the registrar hosts the authoritative nameservers by default,
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but we can change them to others.
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Cloud providers like AWS and Cloudflare run robust authoritative nameservers.
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This hierarchical design makes DNS highly decentralized and robust.
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Now let's walk through the life of a typical DNS query.
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The user types google.com into the browser.
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The browser first checks its cache.
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If it has no answer,
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it makes an operating system call to try to get the answer.
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The operating system call would most likely have its own cache too.
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If the answer isn't there,
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it reaches out to the DNS resolver.
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The DNS resolver first checks its cache.
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If it is not there or if the answer has expired,
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it asks the root name server.
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The root name server responds with the list of the .com TLD name servers.
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Note that since .com is such a common TLD,
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the resolver most likely already caches the IP addresses for those .com TLD name servers.
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The DNS resolver then reaches out to the .com TLD name server and the .com TLD name server
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returns the authoritative name servers for google.com.
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And finally, the DNS resolver reaches out to google.com's authoritative name server,
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and it returns the IP addresses of google.com.
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Now the DNS resolver then returns the IP addresses to the operating system,
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and the operating system returns them to the browser.
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Finally, let's go over some gotchas when updating DNS records for a live high traffic production system.
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DNS propagation is slow because there is a TTL on each DNS record.
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And some of the default TTLs are pretty long.
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Also, not every DNS resolver is a good citizen.
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There are some buggy ones out there that don't honor the TTL.
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To mitigate the risk, there are two practical steps to take.
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First, reduce the TTL for the record that we want to change to something very short,
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say 60 seconds, well in advance before the update actually happens.
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This gives ample time for all the DNS servers to receive the shortened TTL,
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which would allow the actual record update to take effect based on the new shortened TTL.
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Second, leave the server running on the old IP addresses for a while.
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Only decommission the server when traffic dies down to an acceptable level.
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Because some DNS resolvers don't honor the TTL,
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this could take a bit of time and patience.
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This concludes our video on DNS.
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We hope you have a better understanding of how its hierarchical design makes it decentralized and robust.
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Remember, DNS is what translates domain names to IP addresses,
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making it a critical component of the Internet backbone.
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You like our videos, you may like our system design newsletter as well.
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It covers topics and trends in large-scale system design.
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Woordenschat en spreektips bij deze les
Deze spreekles op niveau C1 is gebaseerd op de video “Everything You Need to Know About DNS: Crash Course System Design”. Deze woorden komen het vaakst terug: Dns, server, authoritative, resolver, Tld. Deze video bevat 81 zinnen en 794 woorden om na te spreken. Het gesproken deel duurt 5:29. De spreker praat in een gelijkmatig tempo van ongeveer 145 woorden per minuut, prettig om te shadowen. Slechts 69% van de woorden hoort bij de 3.000 meest gebruikte Engelse woorden, dus de woordenschat is pittig.
Belangrijke woorden in deze video
De 15 moeilijkste woorden uit de video, met uitspraak en betekenis:
| Woord | Uitspraak | Betekenis |
|---|---|---|
| cache zelfstandig naamwoord | /kæʃ/ | cache |
| query zelfstandig naamwoord | /ˈkwɪɹ.i/ | vraag, verzoek |
| robust bijvoeglijk naamwoord | /ɹəʊˈbʌst/ | robuust, degelijk |
| decentralize werkwoord | /diːˈsɛntɹəlaɪz/ | decentraliseren |
| hierarchical bijvoeglijk naamwoord | /ˌhaɪəˈɹɑːkɪkəl/ | hiërarchisch |
| readable bijvoeglijk naamwoord | /ˈɹiː.də.bəl/ | afleesbaar, leesbaar |
| backbone zelfstandig naamwoord | /ˈbækˌboʊn/ | ruggengraat |
| translate werkwoord | /tɹænzˈleɪt/ | vertalen, overzetten |
| gotcha | /ˈɡɑ.tʃə/ | hebbes |
| registrar zelfstandig naamwoord | /ˈɹɛd͡ʒ.ɪsˌtɹɑɹ/ | griffier, trouwambtenaar |
| mitigate werkwoord | /ˈmɪt.ɪ.ɡeɪt/ | mitigeren, verzachten |
| expire werkwoord | /ɪkˈspaɪə(ɹ)/ | aflopen, vervallen |
| assign werkwoord | /əˈsaɪn/ | toewijzen |
| confuse werkwoord | /kənˈfjuːz/ | verwarren, in de war brengen |
| newsletter zelfstandig naamwoord | /ˈn(j)uzˌlɛtɚ/ | nieuwsbrief |
Uitspraak om op te letten
De spreker gebruikt 4 samentrekkingen en verkorte vormen, zoals don't, isn't, we'll. Spreek ze kort uit, zoals je ze hoort.
- De klanken “sh” en “zh”: cache /kæʃ/, shorten /ˈʃɔɹtn̩/, decommission /diːkəˈmɪʃən/, propagation /pɹɑpəˈɡeɪʃən/
- Lange woorden — let op de klemtoon: authoritative /əˈθɔɹɪˌteɪtɪv/, decentralize /diːˈsɛntɹəlaɪz/, hierarchical /ˌhaɪəˈɹɑːkɪkəl/, decommission /diːkəˈmɪʃən/, propagation /pɹɑpəˈɡeɪʃən/
Klanken die Nederlandstaligen lastig vinden:
- Stemhebbende eindmedeklinker — /b/, /d/, /g/, /z/, /v/ niet verscherpen: authoritative /əˈθɔɹɪˌteɪtɪv/, decentralize /diːˈsɛntɹəlaɪz/, confuse /kənˈfjuːz/, conclude /kənˈkluːd/
- /æ/ — opener dan de Nederlandse “e”: cache /kæʃ/, backbone /ˈbækˌboʊn/, translate /tɹænzˈleɪt/, ample /ˈæm.pəl/
- /g/ — een harde plofklank, geen Nederlandse “g”: gotcha /ˈɡɑ.tʃə/, propagation /pɹɑpəˈɡeɪʃən/, mitigate /ˈmɪt.ɪ.ɡeɪt/
Zo oefen je met deze video
- Luister de hele video één keer zonder te spreken en noteer de woorden die je niet kent.
- Spreek zin voor zin na op normale snelheid en herhaal elke zin tot je ritme gelijk is aan dat van de spreker.
- Neem jezelf op en vergelijk met het origineel; let daarbij op woorden als cache, query, robust.
Wat is de Shadowing-techniek?
Shadowing is een wetenschappelijk onderbouwde taalleermethode die oorspronkelijk is ontwikkeld voor professionele tolkentraining en gepopulariseerd door polyglot Dr. Alexander Arguelles. De methode is eenvoudig maar krachtig: je luistert naar native Engelse audio en herhaalt het onmiddellijk hardop — als een schaduw die de spreker volgt met slechts 1–2 seconden vertraging. In tegenstelling tot passief luisteren of grammaticadrills, dwingt shadowing je hersenen en mondspieren om echte spraakpatronen tegelijkertijd te verwerken en te reproduceren. Onderzoek toont aan dat het de uitspraaknauwkeurigheid, intonatie, ritme, verbonden spraak, luisterbegrip en spreekvaardigheid aanzienlijk verbetert — waardoor het een van de meest effectieve methoden is voor IELTS Speaking-voorbereiding en echte Engelse communicatie.