• Blackhole entries, which are manually configured and never age out. Blackhole entries are
configured for filtering out frames with specific destination MAC addresses. For example, to block
all packets destined for a specific user for security concerns, you can configure the MAC address of
this user as a blackhole MAC address entry.
To adapt to network changes and prevent inactive entries from occupying table space, an aging
mechanism is adopted for dynamic MAC address entries. Each time a dynamic MAC address entry
obtained or created, an aging time starts. If the entry has not updated when the aging timer expires, the
switch deletes the entry. If the entry has updated before the aging timer expires, the aging timer restarts.
NOTE:
A static or blackhole MAC address entry can overwrite a dynamic MAC address entry, but not vice versa.
MAC address table-based frame forwarding
When forwarding a frame, the switch adopts the following forwarding modes based on the MAC
address table:
• Unicast mode: If an entry is available for the destination MAC address, the switch forwards the
frame out of the outgoing interface indicated by the MAC address table entry.
• Broadcast mode: If the switch receives a frame with the destination address as all ones, or if no
entry is available for the destination MAC address, the switch broadcasts the frame to all the
interfaces except the receiving interface.
Configuring the MAC address table
The MAC address table configuration tasks include:
• Manually configuring MAC address table entries
• Disabling MAC address learning
• Configuring the aging timer for dynamic MAC address entries
• Configuring the MAC learning limit on ports
These configuration tasks are all optional and can be performed in any order.
NOTE:
• The MAC address table can contain only Layer 2 Ethernet ports and Layer 2 aggregate interfaces.
• This document covers configuring static, dynamic, and blackhole unicast MAC address table entries. Fo
more information about static multicast MAC address table entries, see the
IP Multicast Configuration
Guide
.
Manually configuring MAC address table entries
To help prevent MAC address spoofing attacks and improve port security, you can manually add MAC
address table entries to bind ports with MAC addresses. You can also configure blackhole MAC address
entries to filter out packets with certain destination MAC addresses.
Follow these steps to add, modify, or remove entries in the MAC address table in system view:
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