Where Packets Go

I

Every machine has a number

An IP address is the number other machines use to reach yours. On your apartment Wi-Fi it starts with 192.168, and that number only works inside that Wi-Fi.

Think of your apartment building. Your room number finds you inside the building but it means nothing across town. Your laptop and your PC each have a room number like that, and the trip in this guide uses only those.

Open Konsole on Fedora and ask for yours with:

hostname -I

You may see more than one address printed. Take the one starting with 192.168 and ignore the rest.

II

A packet is a letter that wants an answer

A packet is one small envelope of data traveling between machines. Big things like photos ride as many small packets instead of one giant one.

Every packet carries two addresses on its envelope. One names where it is going and one names where the answer should come back to. That pair is the whole trick, since the receiver needs to know both what arrived and where to reply.

So a packet is a letter that expects a response. The destination says who should open it. The return address says who should get the next letter.

III

The router is the front desk

The router is the box that runs your building Wi-Fi. It knows every room number and hands each packet to the right door.

Mail for another room goes to the front desk first. The clerk reads the destination, walks it to the right door, and never sends it across town. Your router does the same with packets that stay inside your Wi-Fi.

Nothing leaves the building in this guide. The router reads two room numbers and moves paper between them.

IV

There, from Host A to Host B

Your Windows PC is Host A, the sender. Your Fedora laptop is Host B, the receiver. The PC writes a packet with the Fedora address as the destination and its own address as the return address, then hands it to the router.

The router reads the packet and sends it to Host B. It does not open the letter inside. It only reads the envelope and delivers it.

V

Back again, the answer returns

Host B opens the packet, reads it, and writes a response packet back. The two addresses trade places. Now Host A is the destination and Host B is the return address.

The router reads this one and sends it to Host A the same way. Every back and forth on your network is this same swap, a fresh envelope each way with the addresses traded.

VI

Watch the trip

The same round trip, drawn in motion:

1. Host A makes a packet and sends it.
2. The router reads the packet.
3. The router sends it to Host B.
4. Host B takes it in.
5. Host B makes a response packet and sends it.
6. The router reads the packet.
7. The router sends it to Host A.
8. Host A takes in the response.

The blue box around the scene is your local network, so nothing in this trip ever leaves it.

Notice each packet starts inside its sender and ends inside its receiver. The lane between them only ever carries sealed envelopes.

VII

Getting your own IP address

Two commands show your own network. The first prints your IP address and the second lists the neighbors your laptop has already learned.

On Fedora, print your address with:

hostname -I

On the Windows PC open Terminal and print its address with:

ipconfig

In that output find the 192.168 address the same way and write both addresses down, since the diagrams above turn real once your own digits sit in those boxes. Then on Fedora list the neighbors with:

ip neigh

You should see the router and, if the two machines have spoken recently, the Windows PC beside it. If the PC is missing from that list, that only means they have been quiet, and the list fills in next time they talk.

VIII

Ping, the whole round trip

A ping is a test packet that asks the other machine to echo it straight back. Each echo arrives stamped with its round trip time, so one command measures the whole there and back from the animation above.

On Fedora, send three test packets to your Windows PC with:

ping -c 3 192.168.1.20

Replace my last digits with your real Windows address from Getting your own IP address before pressing Enter. The -c 3 flag sends exactly three packets and stops by itself.

You should see three reply lines with times in milliseconds, then a closing line saying no packets were lost. Each time is one full trip, Host A to Host B and back, measured live.

Try the reverse direction too. On the Windows PC open Terminal, type ping followed by your Fedora address, and press Enter. Windows sends four packets and stops by itself, and the replies read the same way.

If the replies never come, work through these in order:

1. Check both machines sit on the same apartment Wi-Fi name, since a hotspot or neighbor network is a different network with different addresses.
2. Reprint both IP addresses, since they change when the router restarts.
3. If nothing answers but both addresses look right, shared Wi-Fi often blocks machines from talking to each other for safety. Copy the exact error text word for word, since that wording is the evidence a helper needs.