Alcatel Carrier Internetworking Solutions Switch/Router 用户手册

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When the switch sees the same 

MAC

 address sending traffic on a different switch port (a 

Duplicate 

MAC

 Address), it assumes the original network device moved. The switch sends a 

trap notifying network management of this station move event. It sends one trap for a device 
move within the same Group and another trap for a device move outside of the home Group.

A station move trap is normally sent after an actual station move. However, certain network 
configurations assign the same 

MAC

 address to different network devices (physical and 

virtual) as standard practice. In these situations, the duplicate 

MAC

 address appears as a 

station move when it is really a normal occurrence in these network configurations. These 
network configurations that use the same 

MAC

 address for different devices include:

•

LAN

 Emulation under Cisco routers. Cisco routers use the same 

MAC

 address for each 

LAN

 

Emulation Client (

LEC

). In 

LAN

 Emulation, each 

ELAN

 needs to be treated as a separate 

LAN

 

and should therefore have a separate 

MAC

 address. 

•

IBM

 Front End Processor (

FEP

). Many 

IBM

 

FEP

s use the same 

MAC

 address assigned to the 

connecting devices for the purpose of redundancy. 

•

DEC

net networks. The 

DEC

net protocol assigns the special 

MAC

 address, 

AA000400XXYY

 

(

XXYY

 is an internal protocol ID) to each 

DEC

net station or routing device regardless of the 

number of physical interfaces.

Initially, duplicate 

MAC

 addresses in these special situations may be no more of a problem 

than extra traps being sent for an event (station move) that did not really happen. However, 
when a large number of these network devices send the same 

MAC

 address out the same 

port, flooding can occur and the switch will eventually shut the port down.

To prevent a port from being shut down, the switch needs some way of knowing the dupli-
cate 

MAC

 addresses originating from the port are not an error condition.

The switch will treat duplicate 

MAC

 addresses as separate addresses as long as they are 

learned from a different Group as the original 

MAC

. Each duplicate 

MAC

 address will use one 

entry in the 

CAM

. Up to 32 duplications of the same 

MAC

 address are supported. Duplicate 

MAC

 addresses learned from virtual ports within the same Group are treated as station moves 

and will generate corresponding traps. If the 

MAC addres

s moves from one 

VLAN

 to another 

VLAN

 within the same Group, the switch will not treat the 

MAC

 addresses as separate.