How traceroute uses TTL
Traceroute sends probes with increasing TTL values. TTL 1 expires at the first router, TTL 2 expires at the second router, and the sequence continues until the destination answers or the maximum TTL is reached.
Network simulation lab
Visual Traceroute Sandbox
Watch TTL values expire hop by hop, inspect simulated ICMP Time Exceeded replies, and compare latency patterns without sending real packets from your browser.
- Runtime
- Browser
- Packets
- 0 real
- Mode
- Sandbox
Trace controls
All route data is generated locally for protocol education.
6%
Route visualization
TTL 0 waits at the source host.
Idle
Traceroute output
3 probes / TTLWhy ICMP appears
When a router decrements TTL to zero, it discards the packet and usually returns ICMP Time Exceeded. The source uses that ICMP reply to learn the router address and approximate round-trip time.
What timeouts mean
Asterisks in traceroute output can mean packet loss, ICMP filtering, rate limiting, asymmetric paths, or a router that forwards packets but does not answer diagnostic probes.
Usage guide
How to use the traceroute sandbox
What this tool shows
It demonstrates how TTL expires at each router, why ICMP Time Exceeded replies appear, and how packet loss changes traceroute output.
How to test it
Pick a route profile, adjust Max TTL and Packet loss, then use Run or Step to compare each hop and the terminal-style output.
When it helps
Use it when learning network diagnostics, teaching TTL behavior, or explaining why real traceroute output can contain asterisks and uneven latency.