3com 2928 Betriebsanweisung
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MAC Address Configuration
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Currently, MAC address configurations related to interfaces only apply to Layer 2 Ethernet
interfaces.
interfaces.
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This manual covers only the management of static and dynamic MAC address entries, not
multicast MAC address entries.
multicast MAC address entries.
Overview
A device maintains a MAC address table for frame forwarding. Each entry in this table indicates the
MAC address of a connected device, to which interface this device is connected and to which VLAN the
interface belongs. A MAC address table consists of two types of entries: static and dynamic. Static
entries are manually configured and never age out. Dynamic entries can be manually configured or
dynamically learned and will age out.
The following is how your device learns a MAC address after it receives a frame from a port, port A for
example:
1) Checks the frame for the source MAC address (MAC-SOURCE for example).
2) Looks up the MAC address table for an entry corresponding to the MAC address and do the
MAC address of a connected device, to which interface this device is connected and to which VLAN the
interface belongs. A MAC address table consists of two types of entries: static and dynamic. Static
entries are manually configured and never age out. Dynamic entries can be manually configured or
dynamically learned and will age out.
The following is how your device learns a MAC address after it receives a frame from a port, port A for
example:
1) Checks the frame for the source MAC address (MAC-SOURCE for example).
2) Looks up the MAC address table for an entry corresponding to the MAC address and do the
following:
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If an entry is found for the MAC address, updates the entry.
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If no entry containing the MAC address is found, adds an entry that contains the MAC address and
the receiving port (port A) to the MAC address table.
the receiving port (port A) to the MAC address table.
After the MAC address (MAC-SOURCE) is learned, if the device receives a frame destined for
MAC-SOURCE, the device looks up the MAC address table and then forwards the frame from port A.
MAC-SOURCE, the device looks up the MAC address table and then forwards the frame from port A.
Dynamically learned MAC addresses cannot overwrite static MAC address entries, but the latter can
overwrite the former.
overwrite the former.
When forwarding a frame, the device adopts the following two forwarding modes based on the MAC
address table:
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Unicast mode: If an entry matching the destination MAC address exists, the device forwards the
frame directly from the sending port recorded in the entry.
frame directly from the sending port recorded in the entry.