set-df

Function

The set-df command configures the DF (Do not Fragment) field of test packet, that is, configures whether test packet fragmentation is allowed.

The undo set-df command restores the default setting.

Format

set-df

undo set-df

Parameters

None

Views

NQA view

Default Level

2: Configuration level

Usage Guidelines

By default, packet fragmentation is allowed.

Usage Scenario

If two hosts need to communicate with each other across multiple networks, the smallest MTU value of the networks is the path MTU value. Packets can be transmitted normally over multiple networks only after the path MTU value is obtained.

If the DF bit of a packet is not configured, and the length of the packet is longer than the MTU value, the packet will be fragmented into several fragments that are shorter than the path MTU value. As a result, the path MTU cannot be detected by sending packets with increasing lengths. To detect the path MTU value, run the set-df command to prohibit packet fragmentation. Then, increase the length of packets sent along the path to find the path MTU value.

Prerequisites

Before using the set-df command, run the test-type command to specify the type of the test instance as trace.

Precautions

The configuration of the DF bit for packets in a running test instance cannot be changed.

Example

# Set the test packet sent without being fragmented.

<sysname> system-view
[sysname] nqa test-instance admin trace
[sysname-nqa-admin-trace] test-type trace
[sysname-nqa-admin-trace] set-df