Hack the Route Start free Open app Forwarding
TTL
A counter in every IP packet, lowered by each router; at zero the packet is dropped.
It stops packets from circling forever in a routing loop. The router that drops a packet sends an ICMP time exceeded back, which is what traceroute relies on. A reply's TTL hints at how many routers it crossed: 64 minus the hops, for Linux senders.