3Com MSH 1005, User Manual

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Advice for Setting Backplane Connections and Avoiding Loops
Considerable care should be taken when setting backplane
connections if there is more than one Switch 1005 installed in your
MSH chassis. If more than one module has multiple connections
enabled on the same VLAN, a network loop can occur, severely
affecting network operation.
For example, consider a pair of Switch modules where all four
backplane connections are enabled and in the same VLAN. If a packet
with a unicast destination address arrives on the backplane E1,
destined for an end-station on backplane E2, both Switch modules will
independently switch the packet onto E2, resulting in duplication.
Packets with broadcast destination addresses will loop continuously
between the two Switch modules. You can avoid this situation by
following these guidelines:
■
If all ports on your network are in the same VLAN, you should connect
all Switch 1005 modules via the Fast Ethernet connection, but only
connect the internal Ethernet backplanes on one Switch 1005.
■
Alternatively, balance the load on your Switch 1005 modules more
effectively by connecting one internal Ethernet connection to each
Switch 1005.
■
If you have implemented multiple VLANs, put each internal Ethernet
connection in a different VLAN on each Switch.