Configuring Arp Fast-Reply; Overview; Function; Operation - H3C MSR 2600 Configuration Manual

Configuring ARP fast-reply

ARP fast-reply is not supported in the current release, and it is reserved for future use.

Overview

Function

In a wireless network, APs are connected to an AC through tunnels, so that clients can communicate with
the AC through APs and can further access the gateway through the AC. If a client broadcasts an ARP
request through the associated AP, the AC needs to send the ARP request to all the other APs, wasting
tunnel resources and affecting forwarding performance. The ARP fast-reply mechanism can solve this
problem.
With ARP fast-reply enabled for a VLAN, the AC can directly answer ARP requests according to the user
information in DHCP snooping entries and ARP snooping entries. For more information about DHCP
snooping, see "Configuring DHCP snooping."

Operation

If the device receives an ARP request with the target IP address being the IP address of the VLAN interface,
it processes the packet as a normal ARP packet. If not, it processes the packet in the following steps:
1. Search the DHCP snooping table for a match.
2. If a match is found and the interface of the entry is the Ethernet interface that received the ARP
request, the device returns no reply. Otherwise, it returns a reply.
3. If no match is found and ARP snooping is enabled, the device searches the ARP snooping table. If
a match is found and the interface of the matching entry is the Ethernet interface that received the
ARP request, the device returns no reply. Otherwise, it returns a reply.
4. If no match is found in both the DHCP snooping and ARP snooping tables, the ARP request is
forwarded to other interfaces except the receiving interface in the VLAN or delivered to other
modules.

Configuration procedure

Enabling the ARP fast-reply mechanism also enables DHCP snooping for the VLAN.
To improve the availability of ARP fast-reply, enable ARP snooping at the same time.
To configure ARP fast-reply:
Step
1. Enter system view.
2. Enter VLAN view.
3. Enable ARP fast-reply.
Command
system-view
vlan vlan-id
arp fast-reply enable
16
Remarks
N/A
N/A
By default, ARP fast-reply is disabled.