dhcp set ttl

Function

The dhcp set ttl command sets the TTL value for DHCP Discover messages after they are forwarded by the DHCP relay agent at Layer 3.

The undo dhcp set ttl command restores the default setting.

By default, the TTL value of DHCP Discovery messages decreases by 1 after they are forwarded by the DHCP relay agent at Layer 3.

Format

dhcp set ttl { unvaried | ttl-value }

undo dhcp set ttl

Parameters

Parameter	Description	Value
unvaried	Indicates that the TTL value of DHCP Discovery messages remains unchanged after the messages are forwarded by the DHCP relay agent at Layer 3. That is, the device does not reduce the TTL value by 1.	-
ttl-value	Specifies a fixed TTL value for DHCP Discovery messages after they are forwarded by the DHCP relay agent at Layer 3.	The value is an integer that ranges from 1 to 255.

Views

System view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

The dhcp set ttl command is used on DHCP relay agents. When a DHCP relay agent forwards DHCP Discovery messages at Layer 3, it reduces the TTL value of the messages by 1 by default. Assume that the TTL value of a DHCP Discovery message received by the DHCP relay agent is 1. If the DHCP relay agent reduces the TTL value by 1, the TTL value changes to 0. The next-hop routing device will discard the message as its TTL value is 0. As a result, the DHCP server cannot receive the DHCP Discovery message forwarded by the DHCP relay agent. To ensure that the DHCP server can receive the DHCP Discovery message sent from the client, run the dhcp set ttl command to set the TTL value of the DHCP Discovery message to a non-zero value after the message is forwarded at Layer 3.

If the DHCP relay agent connects to a special client whose TTL value of DHCP Discovery messages is 1, and if there are routing devices between the DHCP relay agent and DHCP server, run the dhcp set ttl ttl-value command to specify a fixed TTL value (16 is recommended) for DHCP Discovery messages after they are forwarded by the DHCP relay agent at Layer 3.

Prerequisites

The DHCP function has been enabled globally using the dhcp enable command.

Example

# Set the TTL value of DHCP Discovery messages to 16 after the messages are forwarded by the DHCP relay agent at Layer 3.

<HUAWEI> system-view
[HUAWEI] dhcp enable
[HUAWEI] dhcp set ttl 16