Alcatel Carrier Internetworking Solutions Switch/Router 用户手册

Page 22-7

Prior to release 2.1, AutoTracker handled 

VLAN

 assignments for router traffic in 

IP

 and 

IPX

 

network address 

VLAN

s in the same manner as normal traffic. In release 2.1 and later, 

AutoTracker differentiates router traffic from normal traffic and can distinguish traffic that is 
routed through a router from traffic that is generated by a router. 

AutoTracker now determines 

VLAN

 assignments for router interfaces (that is, the 

MAC

 

addresses of router interface ports) in 

IP

 and 

IPX

 network address 

VLANs

 based on router 

update messages generated by the router itself. This minimizes 

VLAN

 leakage and avoids the 

problem situation described on the facing page.

AutoTracker functions on the assumption that data in a frame can be associated with the 
frame’s source 

MAC

 address. For example, if a frame has an 

IPX

 network number of 300, 

AutoTracker assumes that it has received the frame directly and that the source device is a 
member of 

IPX

 network 300. This is not true in the case of routed frames. Routers route 

frames from one network to another by changing the frame’s 

MAC

 header but keeping the 

layer 3 content intact. This can lead to the problem situation described on the facing page. 

In the network on the facing page, Device A gets correctly assigned to 

VLAN

 2 and Device B 

gets correctly assigned to 

VLAN

 3 without problem. The two router interfaces will be assigned 

to the correct 

VLAN

s if AutoTracker learns the router interface MAC addresses from their RIP 

updates. However, this may not happen. The problem situation on the facing page shows 
what can occur if AutoTracker learns the router interface 

MAC

 addresses from traffic routed 

through the router rather than from traffic generated by the router (such as a 

RIP

 update).

To avoid the problem situation on the facing page, AutoTracker now determines if any 

IP

 or 

IPX

 device it has learned is a router. If it is, AutoTracker marks the device as a router, 

unlearns all previous 

VLAN

 assignments for that device, and reassigns the device based on a 

router-generated update packet (such as a 

RIP

 packet). 

AutoTracker determines if a learned device is a router by searching further within the frame. 
For example, if AutoTracker receives an 

IP

 frame, it searches beyond the source 

IP

 address 

and also checks if the 

IP

 frame is a 

RIP

, 

OSPF

, 

BGP

, 

DVMRP

, or 

IGRP

 update. If it is, as 

explained, AutoTracker marks the device as a router, unlearns its previous 

VLAN

 assignments, 

and reassigns it using the router-generated update packet.

AutoTracker recognizes the following types of router-generated frames:

•

IP

 protocol:  

RIP

 frames, 

OSPF

 frames, 

BGP4

 frames, 

DVRMP

 frames, and 

IGRP

 frames

•

IPX

 protocol:  

IPX

 

RIP

 frames and 

SAP

 frames

AutoTracker maintains a record of the devices it has learned are routers. Each time a router-
generated frame is received from a device marked as a router, AutoTracker updates that 
device’s membership in 

IP

 or 

IPX

 network address 

VLAN

s. If a frame received from a device 

marked as a router is not 

IP

 or 

IPX

, 

VLAN

 membership is updated normally.

This special handling of router traffic occurs in 

IP

 

and 

IPX

 network address 

VLAN

s only. Note that it 

does not alter normal 

VLAN

 assignment processes 

such as checking for 

VLAN

 policy matches other 

than 

IP

 or 

IPX

 network address.