Huawei S9300 Configuration Manual page 266

S9300&S9300E Terabit Routing Switch
Configuration Guide - Network Management
The S9300&S9300E implements tracert based on ICMP. Tracert records the gateways that the
ICMP message passes along the path between a source host and a destination. In this manner,
you can check network connectivity and locate the fault.
Figure 5-3 Principle of the tracert operation
Step 1
Step 2
Step 3
Take the networking in
S9300&S9300E. On the S9300&S9300E, run the tracert command. The destination IP address
is the IP address of the log host and other parameters adopt the default values.
1.
2.
3.
4.
5.
6.
In the preceding steps, the tracert program on the source records the IP addresses of the gateways
between the source and the destination through the ICMP Time Exceeded message mentioned
in Step 3.
Issue 01 (2012-03-15)
Switch
Router-A
TTL=1
UDP datagram
ICMP Time Exceeded message
ICMP Destination Unreachable message
Figure 5-3
The S9300&S9300E sends a UDP datagram to the log host, with the TTL value being 1
and the destination UDP port number being 33434.
After receiving the UDP datagram from the S9300&S9300E, Router-A finds that the
destination IP address carried in the datagram is not its own address. Then, Router-A
reduces the TTL value by 1. Finding that the TTL value reaches 0, Router-A sends an ICMP
Time Exceeded message to the S9300&S9300E.
After receiving the ICMP Time Exceeded message, the S9300&S9300E increases the TTL
value and the UDP port number in the UDP datagram by 1 respectively and then sends out
the UDP datagram again.
Perform Step 2 and Step 3, the log host receives the UDP datagram from the
S9300&S9300E.
After receiving the UDP datagram from the S9300&S9300E, the log host finds that the
destination is itself. It begins to process the datagram. The log host tries to find the upper
layer protocol corresponding to the destination UDP port number carried in the datagram.
In most cases, the UDP ports whose number is greater than 30000 are not used by any
protocols. Therefore, the log host sends an ICMP Destination Unreachable message to the
S9300&S9300E to notify the source that the destination port is unreachable.
After receiving the ICMP Destination Unreachable message from the log host, the
S9300&S9300E knows that the UDP datagram has reached the destination and thus stops
running the tracert program.
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
Router-B
TTL=2
TTL=3
as an example to show tracert implementation on the
5 Ping and Tracert
Log Host
251