User's Manual

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Chapter 27 Gratuitous ARP Configuration
27.1 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 SGS-6341 Series 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.
27.2 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
Command
Explanation
Admin Mode and Configuration Mode
show ip gratuitous-arp [interface vlan
<1-4094>]
To display configurations about gratuitous
ARP.