Example

Blossom wants to send a packet to buttercup at port 80.
1. Blossom queries the local DNS server for buttercup's IP address.
2. Blossom broadcasts an IP datagram with destination address of 137.22.11.1 on the local Ethernet.
3. No other computer on the local Ethernet reads the packet because its not addressed to them (unless they are running a sniffer).
4. The router recognizes that this IP will not find its destination of that subnet. It the re-broadcasts the packet on the appropriate sub-net. The source and destination fields are kept the same.
5. Buttercup sees the packet addressed to it and reads it.
Blossom wants to send a packet to bubbles on port 25.
1. Bubbles does not have a real IP number, so it does not exist on the Internet.
2. Blossom somehow (offline) determines that it should instead send a packet to 62.11.12.3. on port 25, hoping that the NAT will do the right thing.
3. Repeat the first four steps of the previous scenario, except that this time the other router picks it up and forwards it to the Internet.
4. The packet goes thru any number of routers on the Internet until it is seen by 62.11.12.3 who then changes the destination IP of the packet to 198.169.0.1 and places it on the local subnet.
5. Bubbles sees the modified packet and reads it.