Network Map

What is a network made of?

Beginner8 minSimulated

Words you’ll meet:

TCP/IP
Routing
Topology

One house, one private /24, one public address. Where private addressing, the default gateway, DHCP, and NAPT all come from.

Private vs public addressing
Subnet masks and the default gateway
DHCP leases
NAPT (port-based NAT)
Layer 2 devices vs layer 3 devices

Layer

Stop 1/10Laptop

Legend

3 kinds of machine, 3 media

Machines

ClientL7Sends requestsAn end user's machine — the browser or CLI that starts the request.
SwitchL2Forwards framesMoves frames within one segment by MAC address; invisible at layer 3.
RouterL3Routes packetsForwards packets between networks by IP address and decrements TTL.

Hops

Wi-FiRadio over a shared medium: variable latency, collisions possible.
EthernetCopper, switched, and wired — the default inside a building.
FiberLong-haul glass — the links between networks and across oceans.

10 steps. Pause, step back or replay any of them.

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Steps

This address is private: it identifies the laptop inside this house and nowhere else, so millions of other homes are using 192.168.1.112 at the same moment. The mask says the first 24 bits are the network, so anything in 192.168.1.0/24 can be reached directly across the LAN. Anything outside it is handed to the default gateway instead.
The phone did not choose its address. It broadcast a request when it joined the Wi-Fi, and the router answered with an address, a mask, a gateway, and a DNS server in one exchange. The lease expires after 24 hours unless the phone renews it, which is how a network reclaims addresses from devices that have left.
Wired Ethernet is a point-to-point full-duplex link into one switch port, so this machine never has to wait for anyone else to stop transmitting. That is most of the reason the wired hop costs 0.05 ms while the Wi-Fi hops cost 0.9 ms, despite Wi-Fi advertising the larger number.
An access point is a bridge, not a router. It lifts an 802.11 frame off the air, rewrites it as an 802.3 frame, and puts it on the wire carrying the same source and destination MAC addresses, without ever opening the IP header. Its 192.168.1.2 address exists only so an administrator can log in and configure it.
The switch forwards frames by destination MAC address, and learns which address sits behind which port by watching the source address of everything that arrives. It holds no IP address on this network and cannot move traffic between subnets: that is the router job, and drawing a switch doing it is the most common way to get a diagram like this wrong.
This is the only device in the house that routes, and the translation it performs is NAPT, not plain one-to-one NAT. It rewrites both the private source address and the source port of every outbound packet, and keeps a table so replies can be matched back to the device that asked. That table is why three devices share one public address, and why a packet arriving unsolicited from outside matches no row and is dropped.
The optical terminal converts between the fibre running to the street and the Ethernet running to the router. In bridge mode it holds no IP address at all, which is why a traceroute from the laptop never shows it: there is nothing at layer 3 for a packet to be addressed to.
The first machine on the path that belongs to somebody else. It leases the public WAN address, and it is also where a well-run ISP drops packets claiming a source address that could not legitimately come from this line. Everything past here needs a globally unique address, which is the entire reason NAPT sits behind it.
Wi-Fi is a shared, half-duplex medium: every device on the channel takes turns, and a sender listens before it transmits rather than talking over anyone. Waiting for a turn is what makes this hop roughly twenty times slower than the wired one.
This single hop costs more than the entire house put together: 6 ms out to the ISP against 0.05 ms across the LAN. Whatever a page load spends inside the home network is noise next to it, which is why slow browsing is almost never a problem on your side of the router.

Details

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The map as a list

8 machines, 7 links

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Network Map

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Machines

Hops

How to use this page

Steps

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The map as a list

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Machines

Hops

How to use this page

Steps

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The map as a list