H3C Technologies H3C SecBlade NetStream Cards - Manual (Page 136)

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• Prevent the virtual IP address of a VRRP group from being used by a host
The master router of a VRRP group can periodically send gratuitous ARP packets to the hosts on the local
network, so that the hosts can update local ARP entries and avoid using the virtual IP address of the VRRP
group.
If the virtual IP address of the VRRP group is associated with a virtual MAC address, the sender MAC
address in the gratuitous ARP packet takes the virtual MAC address of the virtual router. If the virtual IP
address of the VRRP group is associated with the real MAC address of an interface, the sender MAC
address in the gratuitous ARP packet takes the MAC address of the interface on the master router in the
VRRP group.
• Update MAC entries of devices in the VLANs having ambiguous VLAN termination configured
In VRRP configuration, if ambiguous VLAN termination is configured for many VLANs and VRRP groups,
interfaces configured with VLAN termination need to be disabled from transmitting broadcast/multicast
packets and a VRRP control VLAN needs to be configured so that VRRP advertisements can be
transmitted within the control VLAN only. In such cases, you can enable periodic sending of gratuitous
ARP packets containing the VRRP virtual IP address, and the primary IP address or a manually configured
secondary IP address of the sending interface on the subinterfaces. In this way, when a VRRP failover
occurs, devices in the VLANs having ambiguous VLAN termination configured can use the gratuitous
ARP packets to update their corresponding MAC entries in time.
Configuring gratuitous ARP
Follow these steps to configure gratuitous ARP:
To do… Use the command… Remarks
Enter system view system-view —
Enable learning of gratuitous ARP
packets
gratuitous-arp-learning enable
Optional
Enabled by default.
Enable the SecBlade card to send
gratuitous ARP packets upon
receiving ARP requests from
another subnet
gratuitous-arp-sending enable
Required
By default, a device does not send
gratuitous ARP packets upon
receiving ARP requests from
another subnet.
NOTE:
•
You can enable periodic sending of gratuitous ARP packets on a maximum of 1024 interfaces.
• Periodic sending of gratuitous ARP packets takes effect only when the link of the enabled interface goes
up and an IP address has been assigned to the interface.
• If you change the interval for sending gratuitous ARP packets, the configuration is effective at the next
sending interval.
• The frequency of sending gratuitous ARP packets may be much lower than is expected if this function is
enabled on multiple interfaces, if each interface is configured with multiple secondary IP addresses, or
if a small sending interval is configured in such cases.