Operation Manual – ARP
H3C S5500-EI Series Ethernet Switches
Chapter 1 ARP Configuration
1-3
Figure 1-2
ARP address resolution process
When Host A and Host B are not on the same subnet, Host A first sends an ARP
request to the gateway. The destination IP address in the ARP request is the IP address
of the gateway. After obtaining the MAC address of the gateway from an ARP reply,
Host A encapsulates the packet and sends it to the gateway. Subsequently, the
gateway broadcasts the ARP request, in which the destination IP address is the one of
Host B. After obtaining the MAC address of Host B from another ARP reply, the
gateway sends the packet to Host B.
1.1.4 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 port 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.
z
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
outbound port for the entry besides the IP address and MAC address.
z
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 port
