Gratuitous Arp Configuration; Gratuitous Arp Overview - Huawei Quidway S3500 Series Operation Manual

Operation Manual - Network Protocol
Quidway S3500 Series Ethernet Switches

2.3 Gratuitous ARP Configuration

Note:
This chapter only applies to S3552G, S3552P, S3528G, S3528P, S3552F, S3526E,
S3526E FM, S3526E FS and S3526C in S3500 series switches.

2.3.1 Gratuitous ARP Overview

Gratuitous ARP function is to implement the following functions by sending out
gratuitous ARP packets:
By sending gratuitous ARP packets, network devices can figure out whether the IP
addresses of other devices conflict with that of its own.
If the device which sends the gratuitous ARP packet changed its hardware
address (probably, it turns off, has its interface card changed, and then reboots),
this packet can make old hardware address in the cache of other devices update
accordingly.
For example, when a device receives a gratuitous ARP packet with its corresponding
ARP entry existing in the cache of the device, the sending hardware address (such as
Ethernet address) in the gratuitous ARP packet needs to update the content in the
cache. The device must do this every time it receives a gratuitous ARP packet.
Characteristics of gratuitous ARP packets:
The source and destination IP addresses carried by the packet are all native
addresses, and the source MAC address of the packet is native MAC address.
If another device receives a gratuitous ARP packet and finds out that the IP
address in the ARP packet conflicts with that of its own, it sends an ARP reply
back to the device where the ARP packet is from, notifying of the IP address
conflict.
Note:
In Super VLAN networking:
S3526E, S3526E FM, S3526E FS, S3526C: The source MAC address carried by
the gratuitous ARP packet from the Sub VLAN is that of the Super VLAN.
S3552G, S3552P, S3528G, S3528P: The source MAC address carried by the
gratuitous ARP packet from the Sub VLAN is that of the Sub VLAN.
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Chapter 2 ARP Configuration