Interpreting Trace Messages

The Trace is a diagnostic utility which displays the route from host to a destination using ICMP echo packets to the destination. it proceeds a list of hops as a packet is routed through a network. it uses varying TTL values as each router down the path is required to decrement the packet’s TTL by at least 1 before forwarding the packet, the TTL is working just like a hop counter. When the TTL value reaches zero (0), the router sends an ICMP “Time Exceeded” message back to the source.
The trace command sends the 1st  echo packet with a TTL of 1 and then increment the TTL by 1 on each successive transmission, until the destination address responds or until the maximum TTL is reached.

When performing the operation from a Windows computer, the command should be tracert, for example

C:\>tracert fschub.com

C:\>tracert < target IP address >

When performing the trace from a router, the command should be traceroute, for example

Router# traceroute fschub.com

Router# traceroute < target IP address >

Figure 1 shows example output of the tracert command entered on host 4 to trace the route to host 1. The only successful response was from the gateway on Router Peshawar and from router Karak. Trace requests to the next hop (Host 1) timed out, meaning that the next hop (Host 1) did not respond. The results indicate that there is either a failure in the internetwork beyond the LAN or that this host configured not to respond to echo requests used in the trace.

Trace

Figure 2 shows an example output of the tracert command on host 4 to host 2 and the trace is completed successfully.

Trace

Following is an important switch that uses trace command.

d –  This switch with tracert command specifies to not determine addresses to hostnames

-h maximum_hops  -Specifies the maximum number of hops to search for the target

-j host-list – Specifies loose source route along the host-list (IPv4 only)

-w timeout -Waits the number of milliseconds specified by timeout for each reply

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