HP 9304m Installation And Getting Started Manual page 186

customer's network will detect the Layer 2 loop and block a port. The SP network remains unblocked. After the
Preforwarding state, the HP ports change to the Forwarding state and forward data traffic as well as BPDUs.
The default length of the Preforwarding state is five seconds. You can change the length of the Preforwarding
state to a value from 3 – 30 seconds.
Figure 6.2 shows an example of how the Preforwarding state is used.
Figure 6.2 SuperSpan Preforwarding state
During Preforwarding state, SP
forwards all tunneled customer
BPDUs, allowing customer time
to detect the loop and block a port.
In this example, a customer has two links to the SP. Since the SP is running SuperSpan, the SP ports enter the
Preforwarding state briefly to allow the customer ports connected to the SP to detect the Layer 2 loop and block
one of the ports.
NOTE: If you add a new device to a network that is already running SuperSpan, you must enable SuperSpan on
the new device, at least on the VLANs that will be tunneling the customer traffic. Otherwise, the new device does
not use the Preforwarding state. This can cause the wrong ports to be blocked.
Mixing Single STP and Multiple Spanning Trees
You can use SuperSpan in any of the following combinations:
• Customer and SP networks both use multiple spanning trees (a separate spanning tree in each VLAN).
• Customer uses multiple spanning trees but SP uses Single STP (all STP-enabled VLANs are in the same
spanning tree).
• Customer uses Single STP but SP uses multiple spanning trees.
• Customer and SP networks both use Single STP.
The following sections provide an example of each combination.
NOTE: All the combinations listed above are supported when the boundary ports joining the SP SuperSpan
domain to the client spanning trees are untagged. For example, all these combinations are valid in super
aggregated VLAN configurations. If the boundary ports are tagged, you cannot use Single STP in the client
network in combination with multiple spanning trees in the SP SuperSpan domain.
FWD
Cust 1
BLK
Configuring Spanning Tree Protocol (STP)
SuperSpan
root bridge
SP 1
FWD
FWD
SP 2
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