About ARP fast-reply
ARP fast-reply enables a device to directly answer ARP requests according to DHCP snooping entries or ARP snooping entries. ARP fast-reply functions in a VLAN. For information about DHCP snooping, see "Configuring DHCP snooping."
If the target IP address of a received ARP request is the IP address of the VLAN interface, the device delivers the request to the ARP module. If not, the device takes the following steps to process the packet:
Search the DHCP snooping table for a match by using the target IP address.
If a match is found, whether the device returns a reply depends on the type of interface in the matching entry.
If the interface is the Ethernet interface that received the ARP request, the device does not return any reply.
If the interface is an Ethernet interface other than the receiving interface, the device returns a reply according to the matching entry.
If no matching DHCP snooping entry is found and ARP snooping is enabled, the device searches the ARP snooping table.
If the interface in the matching entry is the Ethernet interface that received the ARP request, the device does not return any reply.
If the interface is an Ethernet interface other than the receiving interface, the device returns a reply according to the ARP snooping entry.
If no match is found in both tables, the ARP request is forwarded to other interfaces except the receiving interface in the VLAN, or delivered to other modules.