Traceroute uses ICMP (Internet Control Message Protocol) messages to determine the path that packets take from your computer to a destination host. Specifically, it leverages ICMP Time Exceeded (Type 11) and ICMP Echo Reply (Type 0) messages.
Here's how it works:
Initial Packet: Traceroute sends a UDP (User Datagram Protocol) packet with a TTL (Time to Live) value of 1 to the destination host. The TTL value determines how many hops a packet can make before it is discarded.
First Hop: When the packet reaches the first router (hop), the TTL value is decremented by 1. Since the TTL is now 0, the router discards the packet and sends an ICMP Time Exceeded message back to the source (your computer).
Subsequent Hops: Traceroute then sends another UDP packet with a TTL value of 2. This process repeats, incrementing the TTL value by 1 each time, until the packet reaches the destination host. Each router along the way sends an ICMP Time Exceeded message when the TTL expires.
Destination Host: Once the packet reaches the destination host, it responds with an ICMP Echo Reply message if the destination port is unreachable (since Traceroute uses a port number that is likely to be unused).
Result: By analyzing the ICMP messages received from each hop, traceroute can map out the path from your computer to the destination host.
Example:
If you run traceroute example.com, you might see output like this:
traceroute to example.com (93.184.216.34), 30 hops max, 60 byte packets
1 192.168.1.1 1.234 ms 1.250 ms 1.260 ms
2 10.0.0.1 2.345 ms 2.360 ms 2.370 ms
3 172.16.0.1 3.456 ms 3.470 ms 3.480 ms
...
14 93.184.216.34 15.678 ms 15.690 ms 15.700 ms
Each line represents a hop, showing the IP address of the router and the round-trip time for the packets.
Recommendation:
For more advanced network diagnostics and tracing, you might consider using services like Tencent Cloud's Cloud Trace. This service provides detailed network traffic analysis and can help in troubleshooting complex network issues.