Alcatel Carrier Internetworking Solutions Switch/Router 사용자 설명서

Page 35-6

The following paragraphs describe operational problems you may encounter.

Occasionally, a 

VLAN

 may deadlock. This may be a result of the configuration process you 

used when you set up the 

VLANs

.

If, for example, you have a setup with three switches, as shown in the following figure, the 

VLAN

 can enter a deadlock. In this example, there are two switches, one configured with one 

VLAN

 (Switch X), another configured with two 

VLANs

 (Switch Y), and another switching 

device that connects to the 

VLANs

 (Switch Z).

In this situation, 

VLAN

 2 (V2) in the Switch X is in a loop because it has not learned that it has 

connected to Switch Y with two virtual bridges (V1 and V3), which are inside one switch. 
Since V2 detects a loop, it invokes blocking at the port connected to V1, which results in a 
deadlock. V1 and V3, inside Switch Y, can still communicate, and traffic still exits V2 in 
Switch X, going to V3; however, traffic will not exit V3.

Switch X has detected a
loop and is blocking on
its port connected to
VLAN 1 (V1).

Switch X with VLAN No. 2 (V2)

Switch Y with VLAN No. 1 (V1)
and VLAN No. 3 (V3)

Switch Z