Every computer has an IP address

wikipedia's IP address: 103.102.166.224

UNSW's IP address: 202.58.60.194

It's analogous to the address of your house.

Everything we send is in packets

It's analogous to an envelope.

1. information about the message (header)
2. the message (payload)

What's in a packet header?

Amongst other things:

• destination IP address
• source IP address
• length of the payload
• Time To Live (TTL)

Example

Packet

source: 35.61.125.207
destination: 186.66.18.157
message_length: 12
message: hello there!

But what if there is more than one relay?

As you would expect, IPv4 and IPv6 have different headers.