Allied Telesis AT-S63 - Manual (Page 195)

AT-S63 Management Software Features Guide
Section II: Advanced Operations 195
This is illustrated in this figure. Switch 1 and switch 3 are connected with a
static or LACP trunk of three links. A backup trunk from switch 2 to switch
3 is placed in the blocking state by the spanning tree protocol to prevent a
network loop.
Figure 23. Group Link Control Example 6
Let’s assume that you wanted switch 3 to shutdown the primary trunk to
switch 1 if the active trunk lost a single link. For this you would create a
series of groups to cover all of the possible combinations. Each port would
be designated as an uplink port in one group and as a downstream port in
the other groups. There are three possible combinations, as shown in this
table. The order of the groups is unimportant.
Only one group has to be true for the switch to shut down the ports of the
trunk. If, for instance, port 8 loses connectivity, making group 2 true, the
switch would shut down ports 7 and 9. When connectivity is restored on
port 8, it would enable ports 7 and 9 again.
Switch 1
Network
Switch 3
Switch 2
Switch 4
Ports 7, 8, 9
Table 58. Link Control Groups on Switch 3 in Example 6
Link Control
Group
Upstream Port
Downstream
Ports
1 7 8, 9
2 8 7, 9
3 9 7, 8