Part of series: System Design Roadmap
Week 1 Day 4: DNS & IP - The Internet Phonebook
When you visit google.com, your computer doesn’t know where that is. It needs an IP Address (like 142.250.190.46).
DNS (Domain Name System) is the phonebook that translates names to numbers.
1. How DNS Works (The Journey)
- Local Cache: Browser checks if you visited recently.
- OS Cache: Operation System checks its
/etc/hosts. - Resolver (ISP): Your Internet Provider checks its cache.
- Root Server: “I don’t know google.com, but I know who handles
.com.” - TLD Server (.com): “I know who handles
google.com.” - Authoritative Nameserver: “Here is the IP for
google.com: 1.2.3.4”.
2. DNS Record Types
- A Record: Points a name to an IPv4 address (
1.2.3.4). - AAAA Record: Points a name to an IPv6 address (
2001:...). - CNAME (Alias): Points a name to another name.
www.google.com->google.com.
- MX Record: Mail exchange (for emails).
- NS Record: Nameserver (who is authoritative).
3. IP Addresses
- IPv4: 32-bit (e.g.,
192.168.1.1). Ran out of addresses. - IPv6: 128-bit (hexadecimal). Virtually infinite.
Public vs Private IP
- Public: Unique across the internet.
- Private: Local network only (e.g.,
192.168.x.xor10.x.x.x). NAT (Network Address Translation) connects private to public.
4. Latency
DNS lookup takes time (20ms - 100ms). This is why we use TTL (Time To Live) to cache DNS records. High TTL = Less traffic, slower updates. Low TTL = More traffic, instant updates.
Tomorrow: Mini Project. We build a URL Shortener API! ✂️