arp expire-time

Function

The arp expire-time command sets the aging time of dynamic ARP entries.

The undo arp expire-time command restores the default aging time of dynamic ARP entries.

By default, the aging time of dynamic ARP entries is 1200 seconds, that is, 20 minutes.

Format

arp expire-time expire-time

undo arp expire-time

Parameters

Parameter	Description	Value
expire-time	Specifies the aging time of dynamic ARP entries.	The value is an integer that ranges from 30 to 62640, in seconds. The default value is 1200 seconds, that is, 20 minutes.

Views

System view, Ethernet interface view, GE interface view, XGE interface view, 25GE interface view, 40GE interface view, 100GE interface view, MultiGE interface view, Eth-Trunk interface view, VLANIF interface view, VBDIF interface view, VE interface view, port group view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

To ensure communication reliability, you need to update ARP entries when they are invalid. A dynamic ARP entry has a life cycle. If a dynamic ARP entry is not updated before its life cycle ends, this dynamic ARP entry will be deleted from the ARP table. The life cycle is called aging time. If the entry is updated before its life cycle expires, the aging time of the entry is recalculated.

You can run the arp expire-time command to configure the aging time of dynamic ARP entries, ensuring that dynamic ARP entries are updated in time.

After the aging time of a dynamic ARP entry on an interface expires, the switch sends an aging probe packet (ARP Request packet) from the interface. If the switch receives an ARP Reply packet, it updates this dynamic ARP entry and the aging probe ends. If the switch does not receive an ARP Reply packet after the configured aging probe attempts, it deletes the dynamic ARP entry and the aging probe ends.

Precautions

If the aging time set for a dynamic ARP entry is short, the refreshment for the ARP entry will consume huge number of system resources, causing adverse impacts on other services, a network flapping and even traffic forwarding.
If the aging time set for a dynamic ARP entry is long, the ARP entry will not be promptly updated when it is invalid. For example, if a device fails to work or a network card is changed but the invalid ARP entry has not updated yet, the device sends packets to the peer device based on the existing ARP entry. As a result, the service will be interrupted.

To ensure system stability, use the default value of 20 minutes for a dynamic ARP entry.

If a new aging time is set on an interface that has already learned ARP entries, the new aging time will not take effect on the ARP entries that have been learned, but will take effect on the ARP entries to be learned.

After proxy ARP is enabled on the device, the aging time of ARP entries on user hosts connected to the device should be shortened so that invalid ARP entries on the hosts can be deleted as soon as possible. This decreases packet forwarding failures on the device.

You can adjust the aging parameters of dynamic ARP entries in both the system view and interface view.

If you configure the parameters only in the system view, the configuration takes effect for the dynamic ARP entries learned on all interfaces of the device.
If you configure the parameters in both the system and interface views, the configuration in the interface view takes effect only for the dynamic ARP entries learned on the interface specified.
You cannot adjust the aging parameters of dynamic ARP entries on sub-interfaces. If you configure the parameters on the master interface, the configuration takes effect for the dynamic ARP entries learned on the sub-interfaces. If you do not configure the parameters on the master interface, the configuration in the system view takes effect for the dynamic ARP entries learned on the sub-interfaces.

Example

# Set the aging time of dynamic ARP entries to 600 seconds on VLANIF 100.

<HUAWEI> system-view
[HUAWEI] interface vlanif 100
[HUAWEI-Vlanif100] arp expire-time 600