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VLAN 3
Network 3
Group 2
VLAN 2
Network 2
Device B
Network 3
MAC address = B
Device A
Network 2
MAC address = A
Interface for
Network 2
MAC address = X
Interface for
Network 3
MAC address = Y
➋
➍
Let’s say that the next transmission is a RIP update from the router interface for network 3.
The source of the RIP update is Network 3, MAC address Y. AutoTracker thus assigns MAC
address Y to VLAN 3. MAC address Y is now assigned to both VLAN 2 and VLAN 3.
The same situation can occur with
MAC address X on the router interface for network 2.
Both router interfaces will be members of both VLANs and will transmit RIP updates to both.
If this is an
IPX network and IPX servers are members of these VLANs, they will respond
with router configuration errors. If this is an IP network and devices A and B are IP
workstations listening to RIP, they will respond with invalid network address errors.
(internal or external)
Router
➌
The switch receives the frame from Net-
work 2, MAC address Y, forwards it to
its destination, Device B, and gives it to
AutoTracker to be learned.
Per the policies, AutoTracker assigns the
frame’s source
MAC, MAC address Y, to
VLAN 2. The router interface for net-
work 3 is now a member of network 2!
Omni Switch/Router
The router receives the frame on the interface for Network 2 and
routes the frame to the interface for Network 3. To do this, the router
strips the MAC header from the frame and inserts the MAC address of
from Network 2, MAC address A
Frame
➊
Device A initiates a request to
route a frame to Device B. The
switch forwards the frame to the
router interface for Network 2.
How Routed Frames can Confuse
VLAN Assignment
Frame
from Network 2, MAC address Y
from Network 2, MAC address Y
Frame
its interface for Network 3. The
frame now specifies its source
as Network 2, MAC address Y.
Please Note
This example assumes that
AutoTracker has not yet learned
the
MAC addresses of the router
interfaces for Networks 2 and 3.