The reason why H3C enables tracert path echo ip ttl and ip unreahables commands to be configured

Let's take a look at the manual for the principle of tracert. The following is the part that is not explained in the manual.

First of all, the H3C device turns on path echo command as follows:

Ip unreachables enable

Ip ttl-expires enable

The function of ip ttl-expires enable is that the device in the tracert path makes a "reply ttl timeout" to the ttl-1 of the tracert message, so that the source device can record the address of the device on the way.

When this command is turned on, the address of tracert's next-hop device will be displayed.

The function of ip unreachables enable is that the destination device replies "the destination port is unreachable", so that the source device knows that it has reached the destination device and records the address of the destination device.

This command is for the destination device. If the destination device is not configured, tracert will only display the address of the device along the way. The target device will not show the echo path. You will only see * * *.