Prerequisites, System debugging, Debugging information control switches – H3C Technologies H3C WX5500E Series Access Controllers User Manual
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2.
The first hop (Device B, the first Layer 3 device that receives the packet) responds by sending a
TTL-expired ICMP error message to the source, with its IP address (1.1.1.2) encapsulated. In this
way, the source device can get the address of the first Layer 3 device (1.1.1.2).
3.
The source device sends a packet with a TTL value of 2 to the destination device.
4.
The second hop (Device C) responds with a TTL-expired ICMP error message, which gives the
source device the address of the second Layer 3 device (1.1.2.2).
5.
This process continues until the packet sent by the source device reaches the ultimate destination
device. Because no application uses the destination port specified in the packet, the destination
device responds with a port-unreachable ICMP message to the source device, with its IP address
encapsulated. This way, the source device gets the IP address of the destination device (1.1.3.2).
6.
The source device thinks that the packet has reached the destination device after receiving the
port-unreachable ICMP message, and the path to the destination device is 1.1.1.2 to 1.1.2.2 to
1.1.3.2.
Prerequisites
Before you use a tracert command, perform the tasks in this section.
•
Enable sending of ICMP timeout packets on the intermediate devices (devices between the source
and destination devices).
•
Enable sending of ICMP destination unreachable packets on the destination device.
Using a tracert command to identify failed or all nodes in a
path
Task Command
Remarks
Display the routes from source to
destination.
tracert [ -a source-ip | -f first-ttl | -m max-ttl |
-p port | -q packet-number | -tos tos | -w
timeout ] * host
Available in any view.
System debugging
The device supports debugging for the majority of supported protocols and features and provides
debugging information to help users diagnose errors.
Debugging information control switches
The following switches control the display of debugging information:
•
Protocol debugging switch—Controls whether to generate the protocol-specific debugging
information.
•
Screen output switch—Controls whether to display the debugging information on a certain screen.
As shown in
, assume the device can provide debugging for the three modules 1, 2, and 3. The
debugging information can be output on a terminal only when both the protocol-debugging switch and
the screen-output switch are turned on.