Definition of a MAC Address Table
A MAC address table is used by the switch to record the mappings
between learned MAC addresses of other devices and interfaces on which
MAC addresses are learned, as well as VLANs to which the interfaces
belong. When the switch receives a packet, it searches the MAC address table for the MAC
address of the destination. If the switch finds the MAC address,
it forwards the packet from the corresponding outbound interface in
the MAC address entry. Otherwise, the switch broadcasts the packet
to all interfaces (except the interface on which the packet was received)
in the associated VLAN.
Classification of MAC Address Entries
MAC
address entries are classified into dynamic, static, and blackhole
entries. Service modules may further classify
dynamic MAC address entries according to service types, for example,
secure MAC, MUX MAC, authen MAC, and guest MAC.
Table 1 Characteristics and functions of different MAC address entries
MAC Address Entry Type
|
Characteristics
|
Function
|
Dynamic MAC address entry
|
- Dynamic MAC address entries are obtained by learning the source
MAC address of a packet received on an interface, and can be aged.
- Dynamic MAC address entries do not persist across system restart.
|
- You can check whether data is forwarded between two connected
devices by checking dynamic MAC address entries.
- You can obtain the number of communicating users connected to
an interface by checking the number of specified dynamic MAC address
entries.
|
Static MAC address entry
|
- Static MAC address entries are manually configured. Static MAC address entries are not
aged.
- The static MAC address entries persist across system restart once saved in the
system.
- Interfaces other than that statically bound to the MAC address
in the entry discard packets that originate from this MAC address.
- A static MAC address entry can have only one outbound interface.
- Statically binding an interface to a MAC address does not affect
the learning of dynamic MAC address entries on the interface.
|
A static MAC address entry can be configured to allow an
authorized user to access network resources and prevent other users
from using the bound MAC address to initiate attacks.
|
Blackhole MAC address entry
|
- Blackhole MAC address entries are manually configured. Blackhole MAC address
entries are not aged.
- The blackhole MAC address entries persist across system restart once saved in the
system.
- The switch discards packets from or destined to a blackhole MAC
address.
|
A blackhole MAC address entry can be configured to filter
out unauthorized users.
|