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The blackhole entry is used to discard the frame with the specified source MAC address or
destination MAC address. Users manually set the blackhole entries and send them to each
SIC. Blackhole entries have no aging time.
The dynamic entry will be lost after the system is reset or the interface board is hot swapped or
reset. The static entry and the blackhole entry, however, will not be lost.
Generation of a MAC address entry
MAC address entries are generated automatically or configured manually.
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Automatically Generated MAC Address Entries
MAC address entries are learned by the system automatically. For example, RouterA and
RouterB are connected. When RouterB sends a frame to RouterA, RouterA obtains the
source MAC address (the MAC address of RouterB) from the frame and adds the source
MAC address and the interface number to the MAC address table. When RouterA receives
a frame sent to RouterB again, RouterA can search the MAC address table to find the correct
outbound interface.
The entries in the MAC table will not be valid all the time. Each entry has its own lifetime.
If the entry has not been refreshed at the expiration of its lifetime, the device will delete
that entry from the MAC table. That lifetime is called aging time. If the entry is refreshed
before its lifetime expires, the device resets the aging time for it.
NOTE
The system do not generate MAC address entries when receiving multicast packets or broadcast
packets.
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Manually Configured MAC Address Entries
When creating MAC address entries by itself, the device cannot identify whether the
packets are from the legal users or the hackers. This threatens the network safety.
Hackers can fake the source MAC address in attack packets. The packet with a forged
address enters the device from the other port. Then the device learns a fault MAC table
entry. That is why the packets sent to the legal users are forwarded to the hackers.
For security, the network administrator can add static entries to the MAC table manually
to bind the user's device and the port of the device. In this way, the device can stop the
illegal users from stealing data.
By configuring blackhole MAC address entries, you can configure the specified user traffic
not to pass through a switch to prevent attacks from unauthorized users.
The priority of MAC entries set up by users is higher than that generated by the device
itself.
Aging Time of MAC Addresses
To adapt to the changes of networks, the MAC table needs to be updated constantly. The dynamic
entries automatically created in a MAC address table are not always valid. Each entry has a life
cycle. The entry that has never been updated till its life cycle ends will be deleted. This life cycle
is called aging time. If the entry is updated before its life cycle ends, the aging time of the entry
is recalculated.
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
1 MAC Address Table Configuration
Issue 01 (2014-11-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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