Arp Configuration - 3Com 4200G 12-Port Configuration Manual

198 C 25: ARP C
HAPTER

ARP Configuration

Adding a Static ARP
Mapping Entry Manually
Configuring the ARP
Aging Timer for
Dynamic ARP Entries
ONFIGURATION
By sending gratuitous ARP packets, a network device can:
Determine whether or not IP address conflicts exist between it and other network
■
devices.
Trigger other network devices to update its hardware address stored in their
■
caches.
When the gratuitous ARP packet learning function is enabled on a switch and the
switch receives a gratuitous ARP packet, the switch updates the existing ARP entry
(contained in the cache of the switch) that matches the received gratuitous ARP
packet using the hardware address of the sender carried in the gratuitous ARP packet.
A switch operates like this whenever it receives a gratuitous ARP packet.
ARP entries in an S4200G series Ethernet switch are classified into static entries and
dynamic entries, as described in Table 166.
Table 166 ARP entries
ARP entry
Static ARP entry
Dynamic ARP entry
Table 167 Add a static ARP mapping entry manually
Operation
Enter system view
Add a static ARP
mapping entry
manually
CAUTION:
Static ARP mapping entries are valid as long as the Ethernet switch operates. But
operations that invalidate ARP entries, such as changing/removing VLAN interfaces,
removing VLANs, or removing ports from VLANs, may cause the corresponding ARP
entries being removed automatically.
As for the arp static command, the value of the vlan-id argument must be the ID of
an existing VLAN, and the port identified by the interface-type and interface-number
arguments must belong to the VLAN.
The ARP aging timer applies to all dynamic ARP mapping entries.
Table 168 Configure the ARP aging timer for dynamic ARP entries
Operation
Enter system view
Configure the ARP
aging timer
Generation Method
Manually configured
Dynamically generated
Command
system-view
arp static ip-address mac-address
[ vlan-id interface-type
interface-number ]
Command
system-view
arp timer aging aging-time
Maintenance Mode
Manual maintenance
ARP entries of this type age with
time. The aging period is set by the
ARP aging timer.
Description
Required
The ARP mapping table is empty
when a switch is just started. And
the address mapping entries are
created by ARP.
Description
Optional
By default, the ARP aging timer is
set to 20 minutes.