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Chapter 26 Gratuitous ARP Configuration
26.1 Introduction to Gratuitous ARP
Gratuitous ARP is a kind of A RP request that is sent by the host with its IP address as the destination of the
ARP request.
The basic working mode for XGS3 Chassis Switches is as below: The Layer 3 interfaces of the Chassis
Switch can be configured to advertise grat uitous ARP packets period or the Chassis Switch can be configured
to enable to send gratuit ous ARP packets in all the interfaces globally.
The purpose of gratuitous A RP 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 A RP requests to the gateway to update the MA C address of the gat eway. 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.
26.2 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.
Global Configuration Mode and Interface
Configuration Mode.
ip gratuitous-arp <5-1200>
no ip gratuitous-arp
2. Di splay configurations about gratuitous ARP
Admin Mode and Configuration Mode
show ip gratuitous-arp [interface vlan
<1-4094> ]
Command
Command
Explanation
To enable gratuitous ARP and configure the
interval to send grat uitous ARP request.
The no command cancels the gratuitous ARP.
Explanation
To display configurations about grat uitous
ARP.
26-1
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