Traceroute- Ciscco Wired Host Networking

Traceroute is another helpful piece of network diagnostics software installed on most hosts. Traceroute takes advantage of the TTL in each IP packet to find the path between the local host and a destination.

If you run a traceroute from host A in Figure 4-16 toward  E: 1.  The traceroute application at A will send an IP packet with a TTL of 1 and E’s destination address.

a.  Router C will receive this packet, decrement the TTL, discard the packet, and send an ICMP TTL expired response to A.

b.  The traceroute application at A has now discovered the first hop, or the first router on the path to E is

2.  The traceroute application at A will send an IP packet with a TTL of 2 and E’s destination address.

a.  Router C will receive this packet, decrement the TTL to 1, and forward the packet to D.

b.  Router D will receive the packet, decrement the TTL to 0, discard the packet, and send an ICMP TTL expired response to A.

c.  The traceroute application at A has now discovered the second hop, or the second router on the path to E is D.

3.  The traceroute application at A will send an IP packet with a TTL of 3 and E’s destination address.

a.  Router C will receive this packet, decrement the TTL to 2, and forward the packet to D.

b.  Router D will receive this packet, decrement the TTL to 1, and forward the packet to E.

c.  Host E will receive this packet, decrement the TTL to 0, discard the packet, and send an ICMP TTL expired response to A.

4.  Because the traceroute application at A now has a response from the destination IP address, it will stop sending packets.

Figure 4-17 shows a typical traceroute output.

Figure 4-17 Typical Traceroute Output

If you traceroute to a domain name (such as rule11.tech), most traceroute applications will resolve the name into a destination IP address.

Note