H3C S7500 Series Operation Manual page 236

Operation Manual – MAC Address Table
H3C S7500 Series Ethernet Switches
If the MAC address table already contains MAC-SOURCE, the switch updates the
corresponding MAC address entry.
If MAC-SOURCE does not exist in the MAC address table, the switch adds
MAC-SOURCE and Port 1 as a new MAC address entry to the MAC address
table.
MAC A
MAC B
Port 1
Figure 1-1 Packets forwarded by using a MAC address table
After learning the source address of the packet, the switch searches the MAC address
table for the destination MAC address of the received packet:
If it finds a match, it directly forwards the packet.
If it finds no match, it forwards the packet to all ports, except the receiving port,
within the VLAN to which the receiving port belongs. Normally, this is referred to as
broadcasting the packet.
After broadcasting the packet, the switch will do one of the following based on whether
it receives a response packet:
If the network device returns a packet to the switch, this indicates the packet has
been sent to the destination device. The MAC address of the device is carried in
the packet. The switch adds the new MAC address to the MAC address table
through address learning. After that, the switch can directly forward other packets
destined for the same network device by using the newly added MAC address
entry.
If the destination device does not respond to the packet, this indicates that the
destination device is unreachable or that the destination device receives the
packet but gives no response. In this case, the switch still cannot learn the MAC
address of the destination device. Therefore, the switch will still broadcast any
other packet with this destination MAC address.
To fully utilize a MAC address table, which has a limited capacity, the switch uses an
aging mechanism for updating the table. That is, the switch removes the MAC address
entries related to a network device if no packet is received from the device within the
aging time. Aging time only applies to dynamic MAC address entries.
MAC address Port
MAC A 1
MAC B 1
MAC C 2
MAC D 2
MAC C
MAC D
Port 2
1-2
Chapter 1 MAC Address Table Management