Introduction To System Debugging - H3C S5500-EI series Operation Manual

Operation Manual – System Maintaining and Debugging
H3C S5500-EI Series Ethernet Switches
II. The tracert command
By using the tracert command, you can trace the routers 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 router that first receives the packet) 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 router.
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 router.
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 routers that have
been used to get to the destination device.

2.1.2 Introduction to System Debugging

The device provides various debugging functions. For the majority of protocols and
features supported, the system provides corresponding debugging information to help
users diagnose errors.
The following two switches control the display of debugging information:
Protocol debugging switch, which controls protocol-specific debugging information
Screen output switch, which controls whether to display the debugging information
on a certain screen.
Figure 2-1
screen output switch. Assume that the device can output debugging information to
module 1, 2 and 3. 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 2 System Maintaining and Debugging
2-2