Introduction To System Debugging - H3C S9500 Series Operation Manual

Operation Manual – System Maintaining and Debugging
H3C S9500 Series Routing Switches
II. The tracert command
By using the tracert command, you can trace the switches involved in delivering a
packet from source to destination. This is useful for identification of failed node(s) in the
event of network failure.
The tracert command involves the following steps in its execution:
1) The source device sends a packet with a TTL value of 1 to the destination device.
2) The first hop (the routing device that first receives the packet; the value of TTL
decreases by 1 by each hop) responds by sending a TTL-expired ICMP message
to the source, with its IP address encapsulated. In this way, the source device can
get the address of the first switch.
3) The source device sends a packet with a TTL value of 2 to the destination device.
4) The second hop responds with a TTL-expired ICMP message, which gives the
source device the address of the second routing device.
5) The above process continues until the ultimate destination device is reached. In
this way, the source device can trace the addresses of all the routing devices that
a packet traverses from the source device to the destination device.

1.1.2 Introduction to System Debugging

The device provides various debugging functions. For the majority of protocols and
features supported, the system provides corresponding debugging functions to help
users diagnose errors.
The following two switches control the display of debugging information:
Protocol debugging switch, which controls the output of protocol-specific
debugging information
Screen output switch, which controls whether to display the debugging information
on a certain screen.
Figure 1-1
screen output switch. Only when both are turned on can debugging information be
output on a terminal.
illustrates the relationship between the protocol debugging switch and the
Chapter 1 System Maintaining and Debugging
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