Reverse-path forwarding

Reverse-path forwarding is like when you want to know where a message is coming from before you let it in your house. Imagine it's Halloween and kids are coming to your door for trick-or-treating. You want to make sure they are not strangers or have any bad intentions before you give them candy.

Reverse-path forwarding works the same way for the internet. When a message (also called a packet) wants to come into a computer network, it has to prove it's not a bad message by showing where it's from. If the message is from a trusted source, then it's allowed in. Otherwise, the message is blocked and not allowed to enter the network.

To do this, the computer looks up the source address of the message and sees which path it came from. Then, it checks if the path is the same as the one the message would take if it were to be sent back to the sender. If the path matches, then the message is allowed in. If not, then the message is blocked.

It's like when you are at a party and someone wants to come in, but they need to prove they are invited by telling the person at the door who invited them. If the person says the right name, then they are allowed in. But if they don't say the right name, then they are not allowed to come in.

So, reverse-path forwarding helps keep networks safe by making sure only good messages get in, and bad messages are blocked.