Discovery · Lesson 05

How does DNS help find a destination?

A useful name is easy for people to remember. An IP (Internet Protocol) address is useful to networks. DNS (Domain Name System) helps translate the first into the second before a connection begins.

The naming problem

People remember names. Networks need destinations.

When you visit a website, you usually start with a name such as fusingbits.com. A network cannot deliver traffic using that human-friendly label alone. It needs an address that identifies where the traffic should go.

That creates a translation problem: how do we turn a name into an address without making people memorize numbers?

DNS is a directory, not the destination.DNS helps discover an IP address, but a valid cached answer can also be reused. Finding an address does not guarantee that the service is reachable. Other discovery mechanisms operate in a personal area network (PAN) or local area network (LAN): Bluetooth discovery, the Address Resolution Protocol (ARP), or multicast DNS (mDNS).

Compare the cases

Different ways to find a device or service

01

PAN · Bluetooth

Nearby devices advertise their identity or services. Pairing and Bluetooth discovery usually happen without DNS.

02

LAN · Direct address

For Internet Protocol version 4 (IPv4), ARP maps a known local IP address to a Media Access Control (MAC) address on the local link. The Dynamic Host Configuration Protocol (DHCP) may have supplied the IP configuration first.

03

LAN · Local name

mDNS resolves local names, often ending in .local, without public DNS. Service discovery can use these names to locate a printer or another local service.

04

Internet · Domain name

For a name such as fusingbits.com, DNS can return an IP address. Routing and the connection then carry the traffic to that destination.

Build the model

Four useful stages

01

Name

A label people can read and share, such as fusingbits.com.

02

Lookup

DNS looks up addresses associated with that name. An A record holds an IPv4 address; an AAAA record holds an Internet Protocol version 6 (IPv6) address. A name may return several addresses or no usable address.

03

Address

An IP address gives the network a destination for traffic.

04

Connection

The device uses the answer to begin communicating with the destination.

Mini experiment

Ask the directory

Choose a name. Watch the lookup reveal an address before the connection begins.

This is a simulation, not a live DNS lookup. The names are examples and the addresses belong to the documentation range 203.0.113.0/24; they are not the site's real addresses.

NAMEfusingbits.com
DNS ANSWERNot looked up yet
NEXT STEPWaiting for an address

Ready. Ask DNS for the selected name.

Knowledge check

Test your address model

Answer five questions. The questions and answer order change each time.

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