3Com Switch 8800 Advanced Software V5 Configuration Guide

Configuring ARP 195
4 After receiving the ARP reply, Host A adds the MAC address of Host B into its ARP
mapping table for subsequent packet forwarding. Meanwhile, Host A
encapsulates the IP packet and sends it out.
n
When Host A and Host B are not on the same subnet, a gateway helps finish ARP
address resolution.
ARP Mapping Table After obtaining the destination MAC address, the device adds the IP-to-MAC
mapping into its own ARP mapping table. This mapping is used for forwarding
packets with the same destination in future.
An ARP mapping table contains ARP entries, which fall into two categories:
dynamic and static.
1 A dynamic entry is automatically created and maintained by ARP. It can get aged,
be updated by a new ARP packet, or be overwritten by a static ARP entry. When
the aging timer expires or the interface goes down, the corresponding dynamic
ARP entry will be removed.
2 A static ARP entry is manually configured and maintained. It cannot get aged or be
overwritten by a dynamic ARP entry. It can be permanent or non-permanent.
■ A permanent static ARP entry can be directly used to forward data. When
configuring a permanent static ARP entry, you must configure a VLAN and
outbound interface for the entry besides the IP address and MAC address.
■ A non-permanent static ARP entry cannot be directly used for forwarding data.
When configuring a non-permanent static ARP entry, you only need to
configure the IP address and MAC address. When forwarding IP packets, the
device sends an ARP request. If the source IP and MAC addresses in the
received ARP reply are the same as the configured IP and MAC addresses, the
device adds the interface receiving the ARP reply into the static ARP entry. Now
the entry can be used for forwarding IP packets.
n
Usually ARP dynamically implements and automatically seeks mappings from IP
addresses to MAC addresses, without manual intervention.
Configuring ARP
Configuring a Static ARP
Entry
Follow these steps to configure a static ARP entry:
To do... Use the command... Remarks
Enter system view system-view -
Configure a permanent static
ARP entry
arp static ip-address
mac-address [ vlan-id
interface-type
interface-number ] [
vpn-instance-name ]
Required
No permanent static ARP
entry is configured by default.
Configure a non-permanent
static ARP entry
arp static ip-address
mac-address [ vpn-instance
vpn-instance-name ]
Required
No non-permanent static ARP
entry is configured by default.