MissionRoute one IP datagram from
Route one IP datagram from PC-1 192.168.1.10 to 203.0.113.20. It carries a TCP segment for port 443 — watch what each layer changes.
topology · 192.168.1.0/24 → internet live
ip_header · live valuesnot sent
- source IP · TCP port
- 192.168.1.10:52310
- destination IP · TCP port
- 203.0.113.20:443
- ttl
- 64
- protocol
- 6 (TCP)
- nat translation
- —
PC-1’s private IP plus the encapsulated TCP source port.
The IP destination drives routing; port 443 belongs to the TCP segment carried inside.
Decremented once per router hop.
Tells the receiver which layer-4 handler to use.
Not yet translated.
forwarding_walk
Destination
IDLE
Route lookup — local or remote?
Handed to default gateway
Switch forwards on MAC (L2)
Router rewrites source (NAT/PAT)
TTL decremented across the internet
Final hop to 203.0.113.20
Delivered to the HTTPS listener
Reply un-NATted back to PC-1
Think first · step 1 of 8
PC-1 wants to reach 203.0.113.20. What does it have to decide before sending anything?
what just happened
An IP datagram carries source and destination IP addresses plus a protocol number. Its payload here is a TCP segment with ports. Routers normally preserve the IP addresses, while NAT deliberately rewrites the source mapping. Press send to follow one.
ttl=64 (typical Linux/macOS default) · Windows uses 128
Mission
Route one IP datagram from PC-1 192.168.1.10 to 203.0.113.20. It carries a TCP segment for port 443 — watch what each layer changes.
Questions you will answer
- Why does PC-1 send the packet to the router instead of straight to 203.0.113.20?
- What does the router change in the outgoing packet?
Read it now and keep it in mind — the answer is in what you are about to watch.