How DNS works

README.md

Some example flows for a Medium post about how DNS works.

sequence_01_uncached.websequencediagram

title Uncached DNS request
participant "User agent" as user
participant "ISP DNS" as edge
participant "A" as com
participant "B" as example.com
participant "C" as bar.example.com
participant "D" as foo.bar.example.com

user -> +edge: Lookup foo.bar.example.com
edge -> edge: Do I have a cache for foo.bar.example.com.? No
edge -> edge: Do I have a cache for bar.example.com.? No
edge -> edge: Do I have a cache for example.com.? No
edge -> edge: Do I have a cache for com.? Yes
note over edge,D: In reality, it will have at least 'com.'\nand in popular cases, `example.com.`

edge -> +A: Lookup example.com.
A --> -edge: Records for example.com.
edge -> edge: Follow NS record to Name Server B
edge -> +B: Lookup bar.example.com.
B --> -edge: Records for bar.example.com.
edge -> edge: Follow NS record to Name Server C
edge -> +C: Lookup foo.bar.example.com
C --> -edge: Records for foo.bar.example.com.

edge --> -user: Records for foo.bar.example.com