The iptables REJECT target drops a packet and sends back an error packet
Typically used to send an ICMP administratively-prohibited, or port-unreachable message
It's also possible to send ICMP time-exceeded messages
traceroute traces the path to a destination by sending packet with low TTL values to solicit ICMP time-exceeded messages from routers
The time-exceeded messages reveal the source address of the router for each hop
By responding to low TTL packets with time-exceeded messages, we can fake traceroutes destined to our host