Traceroute works by leveraging the TTL (Time-to-Live) field in IP packets and ICMP (Internet Control Message Protocol) messages to map the network path from a source to a destination. When traceroute is executed with a destination IP address or hostname, it begins by sending ICMP Echo Request packets to the destination with an initial TTL of 1. The TTL specifies the maximum number of hops (router traversals) a packet can make before being discarded. The first packet reaches the nearest router to the source and is discarded because the TTL reaches zero, prompting the router to send an ICMP Time Exceeded message back to the sender. Traceroute then sends subsequent packets with incremented TTL values (2, 3, etc.), allowing them to reach successive routers along the path to the destination. Each router along the path decrements the TTL and forwards the packet, until eventually reaching the destination. By recording the IP addresses of routers that respond with Time Exceeded messages, traceroute maps the complete network path from the source to the destination, revealing the sequence of routers traversed.
Traceroute works step by step as follows: First, the user initiates the traceroute command with a specified destination IP address or hostname. Traceroute begins by sending an ICMP Echo Request packet with a TTL of 1 towards the destination. The packet travels through the network and reaches the first router. The TTL expires at this router, causing it to discard the packet and send an ICMP Time Exceeded message back to the source. Traceroute records the IP address of this first router and increments the TTL value in subsequent packets. It sends the next ICMP Echo Request packet with a TTL of 2, which allows it to reach the second router along the path. This process continues, with traceroute incrementing the TTL value for each packet until it reaches the destination. By analyzing the series of ICMP Time Exceeded messages received and the corresponding IP addresses, traceroute constructs a step-by-step view of the network path taken by packets from the source to the destination.
Traceroute finds a path to a destination by sending multiple ICMP Echo Request packets with increasing TTL values from the source. Each packet travels through the network infrastructure towards the destination, reaching successive routers along the way. When a packet’s TTL expires at a router, the router discards the packet and sends back an ICMP Time Exceeded message to the source. Traceroute captures these messages and records the IP addresses of routers along the path, effectively tracing the route from the source to the destination. By collecting and analyzing the sequence of router IP addresses returned by the ICMP Time Exceeded messages, traceroute identifies the network path taken by packets and provides a detailed map of the routing infrastructure between the source and destination hosts.
Traceroute determines the next hop along the network path by analyzing the IP addresses returned in the ICMP Time Exceeded messages received from routers. When a traceroute packet reaches a router and the TTL expires, the router sends an ICMP Time Exceeded message back to the source with its own IP address. Traceroute uses this IP address to identify the specific router that handled the packet and acted as the next hop towards the destination. By incrementing the TTL value and sending subsequent packets, traceroute continues to identify successive routers along the path until it reaches the final destination. This process allows traceroute to build a sequential list of router IP addresses, showing each hop taken by packets from the source to the destination and providing valuable insights into the network routing infrastructure and connectivity between hosts.