Allied Telesis SwitchBlade x3100 Series User Manual

Introduction Multiple Spanning Tree Protocol (MSTP)
Software Reference for SwitchBlade x3100 Series Switches (Layer Two Switching)
4-80
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.
FIGURE 4-7 MSTP Recovery when Physical Link Blocked
= MST Instance 2 (V_80)
= Physical Link
A
D
= Devices
= Links
V_60
V_80
V_80
V_60
V_80 V_60
B
C
1
2
3
4
1
4
V_80
V_60
D
0.3
A
= MST Instance 1 (V_60)
0.1
0.2
0.1
0.2
0.2
0.1
0.2
0.1
MST Region 1
Regional
Root
Bridge
MSTI 1
Regional
Root
Bridge
MSTI 2
= MST Region 1
MSTP_config_no_secondary_rec
= Physical Link 2 is blocked, VLANs
for MSTI on Physical Links 3 and 4 are
unblocked
V_60
V_80
= CIST Spanning
Tree Instance

Allied Telesis SwitchBlade x3100 Series Specifications

General

Brand	Allied Telesis
Model	SwitchBlade x3100 Series
Category	Switch
Language	English