Alcatel Carrier Internetworking Solutions Switch/Router 사용자 설명서

Page 24-10

Application Example 5 illustrates why port-based policies may be required to establish 
communications in some network situations, such as traversing a backbone. This necessity 
arises because, as explained in How Routing Works Generally on page 24-8, AutoTracker does 
not activate a 

VLAN

 – or its internal router interface – until a port is assigned to that 

VLAN

. 

AutoTracker assigns ports to 

VLAN

s with port policies immediately. However, AutoTracker 

only assigns ports to 

VLAN

s with logical policies when a frame is received from a source 

device that matches the 

VLAN

’s policies. This means that, in some network situations, you 

may need to assign a port policy to a 

VLAN

 to force it active.

The figure below illustrates the problem that can occur. The network below contains two 
Omni Switch/Routers in which three 

IP

 network address 

VLAN

s exist: 

VLAN

 

C

 (

IP

 address 

10.10.10.0), 

VLAN

 

D

 (

IP

 address 20.20.20.0), and 

VLAN

 

E

 (

IP

 address 30.30.30.0). 

VLAN

 

D

 spans 

both Omni Switch/Routers, but has no assigned devices. Routing is enabled for all three 

VLAN

s. A backbone connects port 2 on Omni Switch/Router 1 to port 1 on Omni Switch/

Router 2.

When 

IP

 workstation 10.10.10.1 transmits a frame 

VLAN

 

C

 and its internal router activate. 

When 

IP

 workstation 30.30.30.1 transmits a frame 

VLAN

 

E

 and its internal router activate. All 

subsequent traffic on 

VLAN

 

C

 is transmitted to 

IP

 workstation 10.10.10.1 and all subsequent 

traffic on 

VLAN

 

E

 is transmitted to 

IP

 workstation 30.30.30.1. 

VLAN

 

D

 cannot activate because 

there are no devices that match its network address policy and it has no ports assigned. 
Because 

VLAN

 

D

 is not active, Switches 1 and 2 cannot exchange routing information. Switch 

1 will not be aware of network 30 and Switch 2 will not be aware of network 10.

1

2

3

4

5

6

7

8

1

2

3

4

5

6

12345678

123456

10.10.10.1

10.10.10.

2

20.20.20.

3

20.20.20.

4

30.30.30.

2

With this configuration, 

VLAN

 D

can never become active because it
has neither assigned ports nor
attached devices. Thus, Switches 1
and 2 cannot share routing infor-
mation over the backbone.

30.30.30.1