Alcatel Omni Switch/Router, Руководство пользователя

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AutoTracker VLANs
Page 22-7
How Devices are Assigned to AutoTracker
VLAN
s
(continued)
Router Traffic in
IP
and
IPX
Network Address
VLAN
s
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.
The Problem with Router Traffic
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).
How AutoTracker Handles Router Traffic
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.
Please Take Note
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.