arp purge slowly

Function

The arp purge slowly command enables a device to delete dynamic Address Resolution Protocol (ARP) entries after a delay after an interface in a VLAN goes Down.

The undo arp purge slowly commands restores the default mode of deleting ARP dynamic entries on the specified condition.

By default, a device immediately deletes dynamic ARP entries after an interface in a VLAN goes Down.

Format

arp purge slowly

undo arp purge slowly

Parameters

None

Views

VLANIF interface view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

Normally, if an interface in a VLAN goes Down, a device immediately deletes the dynamic ARP entries learned by the interface. The VLANIF interface must relearn ARP entries to forward user traffic. However, in some special networking scenarios, such as the ring or dual-homing networking, a interface in a VLAN going down does not necessarily mean that its interconnected interface is deleted. The outbound interface of ARP entries may change. In this situation, it will take a long time for the device to relearn ARP entries, interrupting user traffic.

To minimize the preceding impact and accelerate user traffic convergence, run the arp purge slowly command to enable the device to delete dynamic ARP entries after a delay after the interface in a VLAN goes Down.

Configuration Impact

After the arp purge slowly command is configured on an interface, the device does not immediately delete dynamic ARP entries learned by the interface after it goes Down. Instead, it sends ARP detection packets and then deletes or updates ARP entries depending on whether it receives ARP reply packets within the ARP aging time:

If the device does not receive ARP reply packets, it deletes the dynamic ARP entries.
If the device receives ARP reply packets, it updates ARP entries based on information contained in the ARP reply packets.

Precautions

To update ARP entries, a better alternative to ARP aging mechanism is associating MAC entries with ARP entries, because the device learns MAC entries faster. Therefore, to accelerate user traffic convergence, you are advised to enable ARP entry delayed deletion and associate MAC entries with ARP entries.

Example

# Enable a device to delete dynamic ARP entries after a delay if an interface in VLAN 10 goes Down.

<sysname> system-view

[sysname] interface vlanif 10

[sysname-Vlanif10] arp purge slowly