Configuring Tracert - 3Com 4210G Series Configuration Manual

5) Upon receiving the reply, the source device adds the IP address (1.1.1.1) of its inbound interface
to the RR option. Finally, you can get the detailed information of routes from Device A to Device C:
1.1.1.1 <-> {1.1.1.2; 1.1.2.1} <-> 1.1.2.2.
Tracert
Introduction
By using the tracert command, you can trace the Layer 3 devices involved in delivering an IP packet
from source to destination to check whether a network is available. This is useful for identification of
failed node(s) in the event of network failure.
Figure 21-2 Tracert diagram
The tracert function is implemented through ICMP, as shown in
2) The source (Device A) sends a packet with a TTL value of 1 to the destination (Device D). The
UDP port of the packet is a port number that will not be used by any application of the destination.
3) The first hop (Device B) (the Layer 3 device that first 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 (1.1.1.2) of the first Layer 3 device.
4) The source device sends a packet with a TTL value of 2 to the destination device.
5) The second hop (Device C) responds with a TTL-expired ICMP error message, which gives the
source device the address (1.1.2.2) of the second Layer 3 device.
6) The above process continues until the ultimate destination device is reached. No application of the
destination uses this UDP port. Therefore, the destination replies a port unreachable ICMP error
message with the destination IP address 1.1.3.2.
7) When the source device receives the port unreachable ICMP error message, it knows that the
packet has reached the destination, and it can get the addresses of all the Layer 3 devices
involved to get to the destination device (1.1.1.2, 1.1.2.2, 1.1.3.2).

Configuring Tracert

Follow these steps to configure tracert:
To do...
Enter system view
Use the command...
system-view
21-4
Figure 21-2:
Remarks
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