1.1 ARP Overview
ARP dynamically maps Layer 3 IP addresses to Layer 2 MAC addresses. An Ethernet device
must support ARP.
On a LAN, a host or a network device must know the IP address of another host or network
device to send data to it. In addition, the physical address of the destination device must also be
known because IP packets are encapsulated in frames for transmission across a physical network.
Therefore, the mapping from an IP address to a physical address is required. ARP maps IP
addresses to physical addresses.
1.2 ARP Features Supported by the AR150/200
This section describes ARP Features supported by the AR150/200.
The AR150/200 supports dynamic ARP, static ARP, proxy ARP, and ARPing.
ARP
ARP is classified into the following types:
l
Static ARP: Mappings between IP addresses and MAC addresses are configured manually.
l
Dynamic ARP: Dynamic ARP entries are maintained by the ARP protocol.
Proxy ARP
The AR150/200 supports the following types of proxy ARP:
l
Routed proxy ARP
Routed proxy ARP implements communication between devices on the same network
segment but on different physical networks.
If a device connected to the AR150/200 is not configured with a default gateway address
(that is, the device does not know how to reach the intermediate system of the network),
the device cannot forward data packets.
Routed proxy ARP solves this problem. A device sends an ARP Request packet to request
the MAC address of the destination host. After receiving the packet, the AR150/200 enabled
with proxy ARP replies with its own MAC address. The AR150/200 then functions as the
gateway to route packets to the actual destination.
Proxy ARP can also shield topologies of physical networks so that internal hosts of Ethernet
A and Ethernet B on different physical networks but on the same network segment can
communicate.
l
Intra-VLAN proxy ARP
If two users belong to the same VLAN but port isolation is configured in the VLAN, to
enable the two users to communicate, you must enable intra-VLAN proxy ARP on an
interface associated with the VLAN.
If an interface on the AR150/200 is enabled with intra-VLAN proxy ARP, it does not
discard the ARP request packet that is destined for another interface. Instead, it searches
for the corresponding ARP entry of the interface. If the ARP entry is found, the interface
sends the MAC address of the AR150/200 to the sender of the ARP request.
Huawei AR150&200 Series Enterprise Routers
Configuration Guide - IP Service
1 ARP Configuration
Issue 02 (2012-03-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
3