CLI Guide

Table Of Contents

Layer 2 Switching Commands 549

IPDT does not send ARP probes for entries already present in the ARP table

until they age out and ARP packets are exchanged. When IPDT is enabled for

the first time, it may take up to 20 minutes (or the configured ARP timeout)

for the IPDT table to populate.

IPDT is supported for physical (Ethernet) interfaces and for port-channels.

IPDT configuration for Ethernet interfaces is ignored for interfaces which are

part of a port-channel. Configure IPDT on the port-channel instead.

An ARP probe is transmitted on the physical port or port-channel in the

VLAN associated with the device in the IPDT table, with the following fields

set:

The source MAC address is set to the L3 interface MAC on routed

VLANs and to the L2 interface MAC on switched VLANs.

The destination MAC is set to device entry MAC address.

On L3 routed VLANs, the source IPv4 address is set based on the

matching IPv4 subnet on the VLAN interface if it exists or else it is set

to 0.0.0.0. On L2-only switched VLANs, the source IPv4 is set to

0.0.0.0.

The target IPv4 address is set to the IP address of the device entry.

The probe retransmit interval is configurable, with a default value of 30

seconds.

The first probe timeout for each device entry is sequentially distributed from

1 sec to the probe-retransmit-interval value. This is done for pacing the

number of probes that are sent out every second, for performance reasons.

When an interface transitions to the forwarding state, an ARP probe is sent

for all the interface device entries. To avoid duplicate IP conflicts,

transmission of the initial ARP probe is delayed by the probe delay interval

after the interface transitions to the forwarding state. It is possible that a

DHCP client may obtain a DHCP lease before the interval expires.

If the device entry is modified during that delay interval, the initial probe

delay timer is canceled and the probe retransmit timer is started. Whenever

the device entry is updated from ARP Snooping or DHCP Snooping, the

probe retransmit timer is restarted.

Entries in the IPDT table are added on the following events:

• ARP snooping detected a new device.