Layer 3 Forward and ARP Configuration
Chapter 5 Gratuitous ARP Configuration
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5-1
Chapter 5 Gratuitous ARP Configuration
5.1 Introduction to Gratuitous ARP
Gratuitous ARP is a kind of ARP request that is sent by the host with its IP address as
the destination of the ARP request.
The basic working mode for the switch is as below: The Layer 3 interfaces of the
switch can be configured to advertise gratuitous ARP packets period or the switch can be
configured to enable to send gratuitous ARP packets in all the interfaces globally.
The purpose of gratuitous ARP is as below:
1. To reduce the frequency that the host sends ARP request to the switch. The hosts in
the network will periodically send ARP requests to the gateway to update the MAC
address of the gateway. If the switch advertises gratuitous ARP requests, the host will
not have to send these requests. This will reduce the frequency the hosts
’ sending
ARP requests for the gateway
’s MAC address.
2. Gratuitous ARP is a method to prevent ARP cheating. The switch
’s advertising
gratuitous ARP request will force the hosts to update its ARP table cache. Thus,
forged ARP of gateway cannot function.
5.2 Gratuitous ARP Configuration Task List
1
．
Enable gratuitous ARP and configure the interval to send gratuitous ARP request
2
．
Display configurations about gratuitous ARP
1. Enable gratuitous ARP and configure the interval to send gratuitous ARP
request.
Command
Explanation
Global Configuration Mode and Interface
Configuration Mode.
ip gratuitous-arp <
5-1200
>
no ip gratuitous-arp
To enable gratuitous ARP and configure the
interval to send gratuitous ARP request.
The no command cancels the gratuitous
ARP.
2. Display configurations about gratuitous ARP
