Key mapping principles and tools
Time-to-live header fields in IP packets
- As a packet passes through a router, the router decreases the TTL value until it reaches zero: at zero the packet is dropped.
Dropped packets
- When a packet is dropped, an Internet Control Message Protocol (ICMP) error is sent to the source node.
Traceroute
- Uses TTL and ICMP error messages to trace the series of routers a packet traverses from the source node to the destination node.