Explain like I'm five · Network

What is Network Subnetting?

Subnetting, told as a story about splitting one big town into smaller zip-code zones, each with its own post office.

12-345the whole town shares one zip code, so the carrier must search every housewith thousands of houses, the carrier visits every single one

The whole town shares one zip code.With thousands of houses, the carrier has to visit every single one.

one spot's broadcast reaches the whole townwithout zones, congestion and outages spread to everyone

Without zones, congestion and outages spread through the whole town.One spot's broadcast reaches the whole town.

ZONE 112-100~199ZONE 212-200~299ZONE 312-300~399subnetting = splitting one big town into smaller zip-code zoneseach zone gets its own post office — houses are easier to find and manage than in one big town

Subnetting = splitting the town into smaller zip-code zones.Each zone gets its own post office — houses are easier to find and manage than in one big town.

Splitsplits the big town up
Find Fasterknowing the zone sends the envelope straight to that zone's office
Cut With a Rulermarks where the zone part of the address ends
Dedicated Zonecontains congestion and outages
ZIP RULER (SUBNET MASK)front digits — which zone (network part)back digits — which house in that zone (host part)mask — tells where to cut the addressrouting — reads the front digits and ships straight to that zone's office

The ruler (mask) splits an address into front and back digits.A router reads just the front digits and ships straight to that zone.

10 ZONES (2 houses each)wastes a lot of addresses2 ZONES (500 houses each)more congestion, wider outageszones too small or too large both cost you — the right size matters

Zones too small or too large both cost you.Choosing the right zone size matters.

In one breath

Subnetting = dividing one big town (network) into smaller zip-code zones, each with its own post office.

Subnetting divides one IP network into smaller subnets by splitting an address into a network part and a host part with a subnet mask. It lets address space be used efficiently and contains traffic and failures within each zone.

When grown-ups say it

IP Address
The address pointing to a town and a house. The number that identifies a destination.
Subnet Mask
The ruler that splits an address's front from its back. Sets the boundary between network and host parts.
CIDR
Writing the ruler's mark as one short number. Written like /24, for example.
Network/Host Part
The zone number / the house number within it. The two halves an address is split into.
Routing Table
The board that says which zone to ship to. The map a router always checks. → the delivery map that redraws itself
OSI Layer 3
The stage that decides the zone and the path. Addressing and zoning belong to this layer. → the delivery process split into 7 stages
DNS
The address book that finds a zip code by name instead. Covered in depth in the Security field. → the address book you search by name
L4 Switch
The sorter inside a zone who checks the counter number too. Once inside a zone, an L4 switch splits traffic even finer, by counter. → the sorter who checks the port
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