Arp Mapping Table - H3C S7500E Series Operation Manual

Operation Manual – ARP
H3C S7500E Series Ethernet Switches
2) If Host A finds no entry for Host B, Host A buffers the packet and broadcasts an
ARP request, in which the source IP address and source MAC address are
respectively the IP address and MAC address of Host A and the destination IP
address and MAC address are respectively the IP address of Host B and an
all-zero MAC address. Because the ARP request is sent in broadcast mode, all
hosts on this subnet can receive the request, but only the requested host (namely,
Host B) will process the request.
3) Host B compares its own IP address with the destination IP address in the ARP
request. If they are the same, Host B saves the source IP address and source
MAC address into its ARP mapping table, encapsulates its MAC address into an
ARP reply, and unicasts the reply to Host A.
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.
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.
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Chapter 1 ARP Configuration