Application example 5, Traversing a backbone, Application example 5 -10 – Alcatel Carrier Internetworking Solutions Omni Switch/Router User Manual
Page 720: Traversing a backbone -10
Application Example 5
Page 24-10
Application Example 5
Traversing a Backbone
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
Omni Switch/Router 2
Omni Switch/Router 1
IP
Workstation
10.10.10.1
Port 1
Port 2
Port 1
VLAN
C
IP
address 10.10.10.0
10.10.10.
2
Internal
IP
Router
VLAN
D
IP
address 20.20.20.0
20.20.20.
3
20.20.20.
4
Internal
IP
Router
30.30.30.
2
VLAN
E
IP
address 30.30.30.0
VLAN
D
IP
address 20.20.20.0
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.
Backbone
IP
Workstation
30.30.30.1
Port 2