Allied Telesis SwitchBlade x3100 Series Manual page 392

Introduction
0.0
B
VLAN 50
(TDMdata)
0.1
=
A D
Devices
=
1 5
Links
VLAN_STP
STP Network with Multiple VLANs - STP Blocks Two Ports and VLAN is Isolated
FIGURE 4-4
To prevent loops, STP convergence has blocked links 4 and 5. For VLAN 50, this is not a problem; VLAN 50 fol-
lows a physical loop and so actually mimics the loop and needs to be blocked. VLAN 100, however, is a non-
looped VLAN, and so with physical link 4 being blocked, the VLAN on Device A is disconnected from the net-
work and cannot send or receive data.
From this figure two rules follow:
There should be no non-looped VLANs in the STP network.
•
Looped VLANs should follow physical loops of the STP network
•
4.5.4 Example (R)STP Configuration - Standard VLAN
Once the topology stabilizes, in each system one of the ports will become the root port (the one closest to the
root bridge as determined by STP) and the other port(s) become the designated port. The port which is the
root port is considered to be the upstream port and the port which is not the root port (designated port) is
considered to be the downstream port.
4-72
Software Reference for SwitchBlade x3100 Series Switches (Layer Two Switching)
0.2
1
2
0.0
Example (R)STP Configuration - Standard VLAN
A
VLAN 100
(TDMdata)
0.0
VLAN 50
(TDMdata)
0.1
5
0.1
C
VLAN 50
(TDMdata)
0.2
VLAN 100
(TDMdata)
VLAN 100 on Device A is
disconnected
from the network
4
0.1
D
VLAN 100
(TDMdata)
0.0
3
=
VLAN 50
=
VLAN 100
=
Links blocked
(ports blocked)
=
Physical Link