Managing Mac Address Table - H3C S5100-SI Series Operation Manual

Operation Manual – MAC Address Table Management
H3C S5100-SI/EI Series Ethernet Switches
Note:
Under some special circumstances, for example, User B is unreachable or User B
receives the packet but does not respond to it, the switch cannot learn the MAC
address of User B. Hence, the switch still broadcasts the packets destined for User
B.
The switch learns only unicast addresses by using the MAC address learning
mechanism but directly drops any packet with a broadcast source MAC address.

1.1.3 Managing MAC Address Table

I. Aging of MAC address table
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 starts an aging timer for an
entry when dynamically creating the entry. The switch removes the MAC address entry
if no more packets with the MAC address recorded in the entry are received within the
aging time.
Note:
Aging timer only takes effect on dynamic MAC address entries.
II. Entries in a MAC address table
Entries in a MAC address table fall into the following categories according to their
characteristics and configuration methods:
Static MAC address entry: Also known as permanent MAC address entry. This
type of MAC address entries are added/removed manually and can not age out by
themselves. Using static MAC address entries can reduce broadcast packets
remarkably and are suitable for networks where network devices seldom change.
Dynamic MAC address entry: This type of MAC address entries age out after the
configured aging time. They are generated by the MAC address learning
mechanism or configured manually.
Blackhole MAC address entry: This type of MAC address entries are configured
manually. A switch discards the packets destined for or originated from the MAC
addresses contained in blackhole MAC address entries.
Table 1-1 lists the different types of MAC address entries and their characteristics.
1-4
Chapter 1 MAC Address Table
Management