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.

No network calls

Destination

Route profile

Max TTL

Packet loss 6%

Route visualization

TTL 0 waits at the source host.

Idle

Traceroute output

3 probes / TTL

Packet inspector

Current TTL: 0
ICMP result: Waiting
Active hop: Source
Avg RTT: --

TTL logic

Traceroute starts with TTL 1. Each router decrements TTL by one. When TTL reaches zero before the destination, that router returns ICMP Time Exceeded.

Trace summary

Resolved destination: api.example.dev
Simulated IP: 203.0.113.42
Completed hops: 0
Timeout probes: 0

Hop table

TTL	Hop	State

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.

Why 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.