Allied Telesis SwitchBlade x3100 Series Manual page 400

Introduction
For MST Instance 1, the VLAN is blocked on physical link 3, so that no traffic over VLAN 60 can traverse
between bridges C and D. For MST Instance 2, the VLAN is blocked on physical link 4, so that no traffic over
VLAN 80 can traverse between bridges A and D. With this topology, no loops are formed for each MSTP
instance.
With this topology, if link 2 is now physically blocked, there will also be a block over MST Instances 1 and 2
over Physical Link 2. As a result, Bridge C is blocked from the network for MST Instance 2 (VLAN 80) and
Bridges C and D are blocked from the network for MST Instance 1 (VLAN 60).
To correct this, MST Instance 1 will unblock its VLAN (V_60) over physical link 3, and Instance 2 will unblock
its VLAN (V_80) over Physical Link 4. The resulting topology will now allow for no loops and no bridge is iso-
lated. Refer to Figure 4-7.
V_80
MSTP_config_no_secondary_rec
4-80
Software Reference for SwitchBlade x3100 Series Switches (Layer Two Switching)
= Physical Link
= MST Instance 1 (V_60)
= MST Instance 2 (V_80)
1
0.2
Regional
Root
V_60
Bridge
= Physical Link 2 is blocked, VLANs
MSTI 2
for MSTI on Physical Links 3 and 4 are
unblocked
0.1
2
MSTP Recovery when Physical Link Blocked
FIGURE 4-7
Multiple Spanning Tree Protocol (MSTP)
V_60
= CIST Spanning
V_80
Tree Instance
0.3
V_80
A
V_60
MST Region 1
A = Devices
D
1 = Links
4
V_60
C
V_80
= MST Region 1
4
0.1
Regional
Root
V_80
V_60
Bridge
MSTI 1
0.2
3