Arp Table; Configuring Arp; Configuring A Static Arp Entry - 3Com 4510G Configuration Manual

request, in which the target IP address is the IP address of Host B. After obtaining the MAC address of
Host B, the gateway sends the packet to Host B.

ARP Table

After obtaining the MAC address for the destination host, the device puts the IP-to-MAC mapping into
its own ARP table. This mapping is used for forwarding packets with the same destination in future.
An ARP table contains ARP entries, which fall into one of two categories: dynamic or static.
Dynamic ARP entry
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.
Static ARP entry
A static ARP entry is manually configured and maintained. It cannot get aged or be overwritten by a
dynamic ARP entry.
Using static ARP entries enhances communication security. You can configure a static ARP entry to
restrict an IP address to communicate with the specified MAC address only. After that, attack packets
cannot modify the IP-to-MAC mapping specified in the static ARP entry. Thus, communications
between the protected device and the specified device are ensured.
Static ARP entries can be classified into permanent or non-permanent.
A permanent static ARP entry can be directly used to forward packets. When configuring a
permanent static ARP entry, you must configure a VLAN and an outbound interface for the entry
besides the IP address and the MAC address.
A non-permanent static ARP entry has only an IP address and a MAC address configured. If a
non-permanent static ARP entry matches an IP packet to be forwarded, the device sends an ARP
request first. If the sender IP and MAC addresses in the received ARP reply are the same as
those in the non-permanent static ARP entry, the device adds the interface receiving the ARP
reply to the non-permanent static ARP entry. Then the entry can be used for forwarding IP
packets.
Usually ARP dynamically resolves IP addresses to MAC addresses, without manual intervention.

Configuring ARP

Configuring a Static ARP Entry

A static ARP entry is effective when the device works normally. However, when a VLAN or VLAN
interface to which a static ARP entry corresponds is deleted, the entry, if permanent, will be deleted,
and if non-permanent and resolved, will become unresolved.
Follow these steps to configure a static ARP entry:
2-3