arp expire-time

Function

The arp expire-time command sets the aging expiry time of the dynamic Address Resolution Protocol (ARP) entry.

The undo arp expire-time command restores the default setting.

By default, the aging expiry time of the dynamic ARP entry is 1200 seconds, namely 20 minutes.

Format

arp expire-time expire-time

undo arp expire-time

Parameters

Parameter	Description	Value
expire-time	Specifies the aging expiry time of the ARP entry.	The value is an integer ranging from 60 to 62640, in seconds.

Views

Ethernet interface view, Eth-Trunk interface view, VLANIF interface view, or System 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 adjust aging time for ARP entries to ensure their updating.

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.

Configuration Impact

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.

Precautions

To ensure system stability, use the default value of 20 minutes for a dynamic ARP entry.
After Proxy ARP is enabled on a Layer-3 network, you need to shorten the expiry time for an ARP entry to make it invalid as soon as possible. This can reduce the number of invalid packets sent to the Layer-3 network.
The command can be configured globally or on the specified interface. If the command is not configured on the interface, the aging expiry time of a dynamic ARP entry will be the one configured globally. If the command is both configured globally and on the specified interface, the aging expiry time of a dynamic ARP entry will be the one configured on the interface.

Example

# Set the expiry time of the dynamic ARP entry on GigabitEthernet 0/0/1 to 600 seconds.

<sysname> system-view

[sysname] interface GigabitEthernet 0/0/1

[sysname-GigabitEthernet 0/0/1] arp expire-time 600