7.1 MAC Address Table Overview
This section describes the definition of the MAC address table, how MAC address entries are
generated, and how packets are forwarded based on the MAC address table.
Definition
A MAC address table is maintained on each Line Processing Unit (LPU) of theS7700. The MAC
address table stores the MAC addresses of other devices learned by the S7700, the VLAN IDs,
and the outbound interfaces that are used to send data. Before forwarding a data packet, the
S7700 searches the MAC address table based on the destination MAC address and the VLAN
ID of the packet to find the outbound interface quickly. This reduces the number of broadcast
packets.
Creation of MAC Address Entries
MAC address entries can be created dynamically or manually.
l Automatic creation: MAC address entries are learned by the system automatically. The
MAC address table needs to be updated constantly because the network topology always
changes. The automatically created MAC address entries are not always valid. Each entry
has an aging time. If an entry is not updated within the aging time, it is deleted. If the entry
is updated before its aging time expires, the aging timer is reset.
l Manual creation: Automatically created MAC address entries cannot distinguish packets
of authorized users from attack packets. If a hacker sets the source MAC address of attack
packets to the MAC address of an authorized user and connects to another interface of the
S7700, the S7700 learns an incorrect MAC address entry. The packets that should be
forwarded to the authorized user are forwarded to the hacker. To improve interface security,
you can manually create MAC address entries to bind MAC addresses of authorized users
to specified interfaces. This prevents hackers from intercepting data of authorized users.
Manually created MAC address entries take precedence over automatically created MAC
address entries.
Classification of MAC Address Entries
MAC address entries are classified into the following types:
l Dynamic MAC address entries that are learned by an interface after MAC address learning
is enabled.
l Static MAC address entries that are configured manually. Static MAC address entries take
precedence over dynamic MAC address entries.
l Blackhole MAC address entries that are the manually configured and used to discard data
frames with the specified source or destination MAC addresses. Blackhole MAC address
entries take precedence over dynamic MAC address entries.
Packet Forwarding Based on the MAC Address Table
The S7700 forwards packets based on the MAC address table in either of the following modes:
Quidway S7700 Smart Routing Switch
Configuration Guide - Ethernet 7 MAC Address Table Configuration
Issue 01 (2011-07-15) Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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