Alcatel Carrier Internetworking Solutions Switch/Router 用户手册

Page 22-15

Flooding occurs when a frame is received addressed to a device that is unknown to the 
switch or broadcast or multicast frames are received addressed to multiple users. In a typical 
bridged environment, the frame would be forwarded out all ports. However, this is not true 
with 

VLAN

s as 

VLAN

s segment the network into smaller broadcast domains. In this environ-

ment, flooding occurs as follows:

• If the destination address of the frame is unknown buts its source address is known and 

the source device is a member of one or more 

VLANs

, the frame is flooded out all ports of 

all 

VLANs

 in which the source device is a member. Please note the following:

–

If the source device is a member of multiple 

VLANs

, some leakage may occur during 

the flooding process. Leakage may occur only among 

VLANs

 in the same Group—

frames do not leak between Groups.

–

If the source device is a member of multiple 

VLANs

 and some or all of those 

VLANs

 

share the same physical port, only one copy of the frame is forwarded out that port.

–

If the source device is a member of multiple 

VLANs

 that use trunking, only one copy 

of the frame is sent to each trunk port.

• If both the source and destination addresses of the frame are unknown, the frame is 

forwarded to the 

MPX

 for processing (to determine the 

VLAN

 or 

VLANs

 in which the origi-

nating device should be a member) and the frame is flooded out all ports of all 

VLANs

 in 

which the source port is a member.

Frames are forwarded out all ports that are members of the same 

VLAN

s as the source 

MAC

 

address. If the source 

MAC

 address is unknown, it is forwarded out all ports that have 

VLAN

s 

active on the source ports.

Devices that do not share membership in a common 

VLAN

 must use routers to communicate 

with one another. You can configure a virtual router port that is capable of 

IP

 and/or 

IPX

 

routing for each 

VLAN

. By enabling a router port on a 

VLAN

, you are creating a static route 

entry within the switch to that 

VLAN

. If this router port is not configured for a 

VLAN

, then that 

VLAN

 will not be able to communicate with other 

VLAN

s unless an external router is between 

those 

VLAN

s. You may configure up to 16 virtual router ports within a single Omni Switch/

Router. Each 

VLAN

 may contain only one router port. 

. You can enable routing for the default 

VLAN

 when you initially 

create a Group, or when you modify the Group. There are several issues about which you 
should be aware when enabling routing on the Default 

VLAN

. See Application Example 4 in 

Chapter 24, “AutoTracker VLAN Application Examples,” for more information.